Ok, this is just to give everyone a chance to post their "best-ever" fuel economy numbers for their altimas. I own a 2000 altima gle with a drop-in K&N filter, running pure synthetic mobil-1 5w-30 oil, and tires maxed out at 50 psi. Current mileage is 108k with new plugs, cleaned injectors, and cleaned throttle body at performed at 85k. Transmission fluid was changed at 100k. Oil changed regularly every 5000k with K&N oil filters. I also run my oil at about 80% capacity to decrease the time it takes to warm the motor. I never re-fuel with less than 1/8 tank to maximize fuel homogeneity and performance.

To assist me in calculating MPG and control my driving habits, I utilize a an OBD-II Scangauge which provides real-time fuel economy diagnostics, as well as tank average and trip average numbers. My daily commute consists of a 13.5 mile one-way trip; in-bound to work is a net 800 feet elevation gain. The drive is roughly 90% on the highway, and my speed never exceeds 65 mph, but usually I cruise at 55. On a typical round-trip commute, I average 31.5 mpg, which is accomplished through very controlled driving; the inbound commute is typically 28 mpg (sometimes better), with outbound typically 35 mpg (sometimes better). My "best-ever" mpg was achieved coming home from work, where I utilized the ~800 foot decline, where I achieved 40.5 mpg; this was also done on a very warm day (~90 deg F), which helped keep my engine nice and warm and reduced the oxygen density which helped my engine run more lean. AC was turned off, and windows were barely cracked open on the highway.

Feel free to post your numbers! :grinyes:

By not adding the correct amount of oil, your causing your engine bearings to get hot as there is not enough oil to dissapate the heat. This results in more engine friction drag and causes reduced fuel economy :(
Here is the consequences of running your engine low on oil:
http://i137.photobucket.com/albums/q211/Bluerb240/SR20VE/P1010375.jpg
http://i137.photobucket.com/albums/q211/Bluerb240/SR20VE/P1010372.jpg

Running the tank low also causes the fuel varnish and other nasties in the bottom of your tank to be sucked into the fuel pump pre-filter sock :(

Also, when the air is hot there is less oxygen in the air which you pointed out. However, this means there is more petrol than oxygen molecules which means it is running RICHER :) Surprisingly enough, that is why turbocharged cars run an intercooler and most non-turbo cars run a 'Cold Air Induction' system known as a CAI for short. To chill the air means more oxygen and more power potential, resulting in more torque and torque is what makes your fuel economy improve :D

I suppose you dont want to know my twin turbo 5.7L V8 is getting 50MPG in a nearly 3000Lb chassis which gets driven hard occasionally and on a road with plenty of up and down hills. My Pulsar(B13 Sentra chassis) is getting around 60MPG from a V6 Altima motor :D

the best mileage I've gotten from my Altima is 29 mpg on a 300 mile trip to upstate NY. 260 miles were highway.
I use Mobil 5000 5w30 oil. My Alty has 167k I keep my tire pressure at 32 psi
I think over inflating the tires is bad for the suspension and can be hazardous.

Methodmix, at 50 psi you must feel every road bump.

My '08 2.5S has been averaging 28mpg but it only has 3000mi on it.
The oil level will always remain full (very bad if you don't) and the tires are at 32psi. Never exceed your tires rated max psi (check the side wall for that spec). If you do, you risk having the tire blow out on you. I'm sure you don't want that to happen at highway speeds.
My wife (primary driver) commutes 30mi a day, five days a week, averaging 65 to 75mph. When I drive it (not very often) I average between 75 to 100mph. The mpg has never dipped below 26 even at 100mph.
By the way, these mpg listed was this summer with the AC on and usually a full tank.
I plan on getting an intake for it and some 18" wheels and tires for summer use. The tires should allow for close to 44psi max pressure.
By the way, the altitude where I live is around 5000 plus feet (Colorado). Higher altitude if we head to the mountains but we usually take our big cruiser bike for that (summertime).:biggrin:

i just have to say methodmix that you do some dumb stuff with your car. im not really going to get into all of it but the worst is 50psi on your tires? dude you must be retarted put them at 32-35 and your ride and mpg will be better i promise

By not adding the correct amount of oil, your causing your engine bearings to get hot as there is not enough oil to dissapate the heat. This results in more engine friction drag and causes reduced fuel economy :(

Please let me clarify that when I say low, I'm referring to an oil level that is at the lower limits that is within the safe and recommended range as indicated by the dipstick. I absolutely make sure it doesn't get lower than these limits. Thank you for that illuminating example of running too low on oil! :naughty:

Running the tank low also causes the fuel varnish and other nasties in the bottom of your tank to be sucked into the fuel pump pre-filter sock :(

Agreed, which is why (as I said earlier) I never let my tank get below 1/8 of a tank.

Also, when the air is hot there is less oxygen in the air which you pointed out. However, this means there is more petrol than oxygen molecules which means it is running RICHER :)

Actually my scangauge says otherwise, but I will confirm this later and provide an excel spreadsheet of air intake temps vs. fuel trim at various levels of engine load. And from a physics/chemistry standpoint, you are also incorrect, as less oxygen requires a leaner fuel mixture to reach ideal an stoichiometric combustible air-fuel mixture.

Surprisingly enough, that is why turbocharged cars run an intercooler and most non-turbo cars run a 'Cold Air Induction' system known as a CAI for short. To chill the air means more oxygen and more power potential, resulting in more torque and torque is what makes your fuel economy improve :D

While it is true that colder air and engine mods that produce a higher density of oxygen into your throttle body provides more horsepower and torque, the side-effect is a more rich fuel mixture which must be added to compensate the higher-than-normal density charge of oxygen for ideal stoichiometric combustion (see above), which is all electronically controlled by your vehicle's ECU. Diesel engine's exhibit the opposite effect due to the different stoichiometric properties and the direct-injection characteristics of most diesel engines; so if you are referring to a diesel engine, you are most likely correct in your assessment.

I suppose you dont want to know my twin turbo 5.7L V8 is getting 50MPG in a nearly 3000Lb chassis which gets driven hard occasionally and on a road with plenty of up and down hills. My Pulsar(B13 Sentra chassis) is getting around 60MPG from a V6 Altima motor :D

Actually, that is quite an impressive achievement on both accounts. What is the percentage of highway miles for both MPG estimates?

the best mileage I've gotten from my Altima is 29 mpg on a 300 mile trip to upstate NY. 260 miles were highway.
I use Mobil 5000 5w30 oil. My Alty has 167k I keep my tire pressure at 32 psi
I think over inflating the tires is bad for the suspension and can be hazardous.

Methodmix, at 50 psi you must feel every road bump.

Haha! :naughty:

I do in fact feel every road bump. FYI, my tires are rated for 44 psi (V-rated Michellin Hydroedge) and most tires can tolerate small wiggle room for overinflation. 50 psi is as high as I have ever gone, and after nearly 2000 miles, everything seems normal (except the bumps are more apparent). Higher tire pressure does result in more wear on your suspension as the energy from each bump is not as easily absorbed by the tire under those circumstances. What hazards are you referring to? Everything that I've read suggests there are more hazards from underinflation than overinflation.

i just have to say methodmix that you do some dumb stuff with your car. im not really going to get into all of it but the worst is 50psi on your tires? dude you must be retarted put them at 32-35 and your ride and mpg will be better i promise

Please go into it, I'd love to hear your explanation. If the worse of it is overinflation, than I should have very little to worry about (read my above comments). Let me assure you, I am by no means mentally handicapped and I more than welcome a debate on this topic. :biggrin:

well with the tank getting low and the low oil levels that you clarified above those were my two biggest concerns cause with the richer air blah blah blah i would have no clue what i was talking about if i tried to argue that haha. sorry if i came accross as making you sounding retarted:icon16: that wasnt my point now that you clarified some stuff :wink:

i do have to say though that the day you got 40.5mpg with it being about 90 degrees with no a/c and windows barely cracked you had to be one hot person lol

i do have to say though that the day you got 40.5mpg with it being about 90 degrees with no a/c and windows barely cracked you had to be one hot person lol

Haha, well I'm in Southern Cali, so it's a dry heat, but yeah it wasn't the most comfortable experience. I come from south FL, so going from 90 degrees with humidity to almost no humidity is quite a big change. :grinyes:

well with the tank getting low and the low oil levels that you clarified above those were my two biggest concerns cause with the richer air blah blah blah i would have no clue what i was talking about if i tried to argue that haha. sorry if i came accross as making you sounding retarted:icon16: that wasnt my point now that you clarified some stuff :wink:

And honestly, my goal in starting this thread wasn't so much to debate my techniques in achieving high MPG's as it was to see how my efforts have compared to others. I understand we can't do apples-to-apples comparisons here, which is why I tried to be as specific as I could regarding my vehicle's condition and my driving habits. At any rate, do you at least keep track of your MPGs?

Please let me clarify that when I say low, I'm referring to an oil level that is at the lower limits that is within the safe and recommended range as indicated by the dipstick. I absolutely make sure it doesn't get lower than these limits. Thank you for that illuminating example of running too low on oil! :naughty:

Maybe you should work for Nissan? The dipstick is for gauging how much oil to add, not for working out how much oil you can safely remove from the engine. Less oil results in more engine wear as the heat is not dispersed correctly through the rest of the fluid in the sump. Strangely enough, all these people fitting baffled oversize sumps or external oil coolers must be wasting their money in an attempt to cool their oil :rolleyes: Not enough oil and your oil pickup sucks up a nice bubble of air, then you will know about it ;)

Agreed, which is why (as I said earlier) I never let my tank get below 1/8 of a tank.

Thats still enough when you consider you have fuel being returned to the fuel tank via the fuel pressure regulator return line which introduces fuel swirl, lifting the 'crap' off the bottom of the tank.

Actually my scangauge says otherwise, but I will confirm this later and provide an excel spreadsheet of air intake temps vs. fuel trim at various levels of engine load. And from a physics/chemistry standpoint, you are also incorrect, as less oxygen requires a leaner fuel mixture to reach ideal an stoichiometric combustible air-fuel mixture.

They have this amazing thing called Air:Fuel ratio, as your air is being heated there is less oxygen content in the same cubic capacity so the ratio goes from say 14.7 molecules of air:1 molecule fuel and becomes 12 parts air:1 part fuel, which is rich. Did you pass basic physics and maths? :eek7:

Your 'theories' have also completely discounted volumetric efficiency. The idea behind fuel economy is to produce the most amount of torque in the desired cruising speed rpm range, this occurs by filling the cylinder efficiently. As you have more torque, less throttle angle is required and THUS reducing engine load. The trade off of this is that you are constantly in 'lean cruise' mode where the ECU references the O2 sensor to maintain a set O2 sensor voltage(0.44V in most cases) for the leanest fuel mixture available. Ignition timing tables from a cold intake temperature also increase which provides better combustion and more energy released from the air:fuel mixture.

Forget the scan gauge for a second, have you ever seen the stock ECU coding and how it reacts to different sensor inputs? I have :cool: I actually tune them ;)

Here is a sample of the software I use:
http://i252.photobucket.com/albums/hh40/iamhappy46/SSS35L/VQ35_fuel.jpg
Dark blue is under O2 sensor control and when driven sensibly, never comes off the blue cells.

While it is true that colder air and engine mods that produce a higher density of oxygen into your throttle body provides more horsepower and torque, the side-effect is a more rich fuel mixture which must be added to compensate the higher-than-normal density charge of oxygen for ideal stoichiometric combustion (see above), which is all electronically controlled by your vehicle's ECU. Diesel engine's exhibit the opposite effect due to the different stoichiometric properties and the direct-injection characteristics of most diesel engines; so if you are referring to a diesel engine, you are most likely correct in your assessment.

I suppose my utes 15.3 AFR's are considered rich in your book? I have no boost when driving at cruising speeds BUT the turbo exhaust wheels have a nice side effect of effective exhaust gas scavenging from the cylinders as each exhaust port opens. When the engine comes on boost, the increased torque(600+FtLbs) means that I hardly need any throttle angle and thus without any engine load, the engine can remain in lean cruise mode for most of the journey. The V6 has headers which also help in exhaust gas scavenging for a more efficient engine. No left over exhaust gas in the cylinder to pollute my nice fresh air:fuel being sucked in means more effective combustion without needing to reduce ignition timing to offset the polluted mixtures desire for pre-ignition ;)

Diesel injection is a whole different kettle of fish, the mixture needs to be lean enough to 'burn' and hence why better economy can be gained. The new turbo diesel Hyundai i30 for example, can have the factory ECU modified for more boost and leaner mixtures for over 600 miles to a single tank ;)

Actually, that is quite an impressive achievement on both accounts. What is the percentage of highway miles for both MPG estimates?

80% Highway speeds(60MPH), 20% city speed(30MPH) with my work gear in the vack.

Also, on the topic of fuel tanks. Did you know that when you run your tank low... the fuel being pumped up to the engine bay under pressure is actually heated both by the pressure and the warm fuel rail. As excess fuel is being returned to the fuel tank, this warmed fuel enters the fuel tank and with a full tank, the fuel is quickly cooled. In a nearly empty tank, the warm fuel warms the remaining fuel in a cycle. This warmed fuel then creates fuel vapours, that thanks to the carbon canister fitted to modern fuel injected vehicles is consumed by the engine. Your 'scan gauge' cannot account for this unmetered fuel vapour as it is only basing its readings of injector pulse trim and other ECU sensor inputs. Thus, the scan gauge accuracy is questionable.

50psi tyre pressure would be like eating laxative chocolate coated peanuts, you will feel every bump.

yea i have been to colorado before, i live in sc so we have killer humidity here too and it was great in co with no humidity at all hardly

Maybe you should work for Nissan? The dipstick is for gauging how much oil to add, not for working out how much oil you can safely remove from the engine. Less oil results in more engine wear as the heat is not dispersed correctly through the rest of the fluid in the sump. Strangely enough, all these people fitting baffled oversize sumps or external oil coolers must be wasting their money in an attempt to cool their oil :rolleyes: Not enough oil and your oil pickup sucks up a nice bubble of air, then you will know about it ;)

LOL, no thanks I've got a decent job already! :grinyes: I see you're point with low oil levels, and engine wear was definitely something that was in the back of my mind, although I sort of rolled the dice and figured 1/2 quart less than full was more-or-less inconsequential in terms of engine wear. I also considered that after a certain number of miles in driving my oil would start to burn off, so I've tried to check on oil levels on a consistent basis and add more as necessary. But you have a valid point, in that it isn't work taking a chance with even a 1/2 quart less than full just to get warmer engine temps for better thermal efficiency because the gain in friction probably outweighs those gains, not to mention I'd rather keep my engine running optimal and lasting as long as it is designed to. Thanks for that advice! :grinno:

Thats still enough when you consider you have fuel being returned to the fuel tank via the fuel pressure regulator return line which introduces fuel swirl, lifting the 'crap' off the bottom of the tank.

Nice explanation! I think though that the sloshing around from stop-and-go driving coupled with making 90 degree turns introduces even more mixing (compared to the returned fuel from the pressure regulator) at the bottom of the tank. Either way you're right about the consequences of running an engine on a low fuel tank.

They have this amazing thing called Air:Fuel ratio, as your air is being heated there is less oxygen content in the same cubic capacity so the ratio goes from say 14.7 molecules of air:1 molecule fuel and becomes 12 parts air:1 part fuel, which is rich. Did you pass basic physics and maths? :eek7:

Actually, I did pass engineering level physics with a B and math up to ordinary differential equations with an A. Also passed thermodynamics and basic chemistry with an A. But my degree is in a non-mechanical and non-engineering field, so my expertise (or lack thereof?) is purely based on theory and information that I've gathered from other sources. Either way, your sarcasm is warranted and I welcome the humor! :naughty: While you are correct in principle, you are forgetting to mention is that the ECU is programmed to achieve near perfect "stoich" (i.e., 14.7:1 air/fuel mixture as you stated above) by utilizing incoming and outgoing oxygen at multiple times per second (virtually in real time), and since the ECU is constantly trying to achieve the ideal mixture for complete combustion, the fuel trim is dynamically adjusted, and in the case of warmer air, fuel consumption is reduced.

Your 'theories' have also completely discounted volumetric efficiency. The idea behind fuel economy is to produce the most amount of torque in the desired cruising speed rpm range, this occurs by filling the cylinder efficiently. As you have more torque, less throttle angle is required and THUS reducing engine load. The trade off of this is that you are constantly in 'lean cruise' mode where the ECU references the O2 sensor to maintain a set O2 sensor voltage(0.44V in most cases) for the leanest fuel mixture available.

You're correct, and it's my fault for not addressing this issue. You can also utilize your ideal torque range to figure out the ideal RPM range for most efficient acceleration. A scangauge can really help with this since you can view both real-time fuel consumption and cumulative fuel economy simultaneously. Also, your ECU description partially addresses my last point above.

Ignition timing tables from a cold intake temperature also increase which provides better combustion and more energy released from the air:fuel mixture.

This is correct if you assume that the engine has already reached optimal operating temperature. A significant problem with cold air is that it reduces the amount of time it takes for your engine to warm up to optimal temps, and your ECU compensates by running a rich mixture until then engine has reached optimal temps. What you are probably referring to is a cold-air intake, which can theoretically pull "colder" air by being positioned lower in the engine bay and through insulation from the radiating heat of the motor itself. If we assume relatively warm outside (ambient) air temps, then I believe a cold-air intake can be very effective. The other issue with cold-air intakes is they typically increase the "flow-rate" of oxygen into the throttle body; the MAF sends this information to the ECU, which compensates by adding more fuel to the mixture. Under full-throttle conditions, a cold-air intake will ultimately result in more fuel consumed for that period of time compared to a stock air intake system; however, you can offset this consumption by utilizing the extra power and torque as you've mentioned to maintain a constant cruise speed more efficiently.

Forget the scan gauge for a second, have you ever seen the stock ECU coding and how it reacts to different sensor inputs? I have :cool: I actually tune them ;)

I have not, but that is a very interesting example. I am assuming that this data you provided applies to an engine that has already reached optimal operating temperature. This does a good job of showing the ideal load/rpm combination. What vehicle was this data taken from? It would also be interesting to see air intake temps as a function of load and the percent differences from the ideal stoich mixture.

I suppose my utes 15.3 AFR's are considered rich in your book? I have no boost when driving at cruising speeds BUT the turbo exhaust wheels have a nice side effect of effective exhaust gas scavenging from the cylinders as each exhaust port opens. When the engine comes on boost, the increased torque(600+FtLbs) means that I hardly need any throttle angle and thus without any engine load, the engine can remain in lean cruise mode for most of the journey. The V6 has headers which also help in exhaust gas scavenging for a more efficient engine. No left over exhaust gas in the cylinder to pollute my nice fresh air:fuel being sucked in means more effective combustion without needing to reduce ignition timing to offset the polluted mixtures desire for pre-ignition ;)

Wow, that is actually quite lean. Under what conditions are you achieving 15.3 AFR? I would assume very low load and low rpm that is near the peak of your torque curve. According to the numbers you just showed on that chart, the highest AFR I calculated was 15.05. Either way, I don't think your ECU could manage 15.3 for very long but I could be wrong. How many pounds of boost are you running?

Diesel injection is a whole different kettle of fish, the mixture needs to be lean enough to 'burn' and hence why better economy can be gained. The new turbo diesel Hyundai i30 for example, can have the factory ECU modified for more boost and leaner mixtures for over 600 miles to a single tank ;)

And unfortunately this vehicle probably won't be 50-state legal due to NOx emissions. :disappoin It would be nice to see more 4-cyl turbo diesel cars here in the US.

80% Highway speeds(60MPH), 20% city speed(30MPH) with my work gear in the vack.

I like how you keep your highway speeds relatively low. :grinyes: This helps reduce the losses associated with aerodynamic drag. Do you practice any hypermiling techniques?

Also, on the topic of fuel tanks. Did you know that when you run your tank low... the fuel being pumped up to the engine bay under pressure is actually heated both by the pressure and the warm fuel rail. As excess fuel is being returned to the fuel tank, this warmed fuel enters the fuel tank and with a full tank, the fuel is quickly cooled. In a nearly empty tank, the warm fuel warms the remaining fuel in a cycle. This warmed fuel then creates fuel vapours, that thanks to the carbon canister fitted to modern fuel injected vehicles is consumed by the engine. Your 'scan gauge' cannot account for this unmetered fuel vapour as it is only basing its readings of injector pulse trim and other ECU sensor inputs. Thus, the scan gauge accuracy is questionable.

I have read up on this somewhere, but when considering a 4 cyl vehicle, the amount of excess being returned to the tank is likely to be very insignificant. I'm not sure if my vehicle has a carbon canister, but I do know it has an evaporator canister; are these the same thing? The scan gauge is definitely not 100% accurate, but it's a pretty darn good first-order approximation. I've compared scan gauge estimates to pump estimates when refilling my tank on dozens of occasions, and it has a tendency to underestimate fuel consumption by no more than 4.1 percent (the worst its ever done) when calculated for about a 12 gallon tank consumption. This amounts to an error of 0.5 gallons for a 12 gallon tank, which for a worse-case-scenario, isn't too bad in my opinion. The scangauge also has a +/- fudge factor calculator built in, so that any systematic biases that the scangauge produces can be partially corrected to produce more accurate trip MPG estimates.

50psi tyre pressure would be like eating laxative chocolate coated peanuts, you will feel every bump.

Indeed I do, especially on these dilapidated southern California freeways. :disappoin But it's a small price to pay for the money I save on gas.

LOL, no thanks I've got a decent job already! :grinyes: I see you're point with low oil levels, and engine wear was definitely something that was in the back of my mind, although I sort of rolled the dice and figured 1/2 quart less than full was more-or-less inconsequential in terms of engine wear. I also considered that after a certain number of miles in driving my oil would start to burn off, so I've tried to check on oil levels on a consistent basis and add more as necessary. But you have a valid point, in that it isn't work taking a chance with even a 1/2 quart less than full just to get warmer engine temps for better thermal efficiency because the gain in friction probably outweighs those gains, not to mention I'd rather keep my engine running optimal and lasting as long as it is designed to. Thanks for that advice! :grinno:

No problem, I can see the 'theory' coming through but real world application differs and for the $1 worth of oil your saving, the effects to your engine are just not worth the 'potential' fuel savings.

The best one I had was years ago, when a customer had a V8 who refused to change the oil or coolant, only changing spark plugs every 12,000 miles. The money he saved on servicing(about $500 a year) meant that after 8 years, the motor seized and he had the money to fit a new motor which he did the same thing to :shakehead All in the interests of saving money :cwm27:

Nice explanation! I think though that the sloshing around from stop-and-go driving coupled with making 90 degree turns introduces even more mixing (compared to the returned fuel from the pressure regulator) at the bottom of the tank. Either way you're right about the consequences of running an engine on a low fuel tank.

As the fuel return is in the centre of the tank, it does create a nice vortex when it is being returned. This is most evident, when your at low engine speeds and the injectors are pumping minimal fuel so excess fuel flow is returned to the tank. Your factory fuel pump is flowing close to 45 gallons per hour, so based on your fuel economy at highway speed then your returning about 43 gallons of fuel to the tank every hour :(

Yes, the carbon canister and evapourative canister are the same thing. Filled with carbon, it is a 'filter' to stop any 'nasty' fumes being sucked into the motor.

Actually, I did pass engineering level physics with a B and math up to ordinary differential equations with an A. Also passed thermodynamics and basic chemistry with an A. But my degree is in a non-mechanical and non-engineering field, so my expertise (or lack thereof?) is purely based on theory and information that I've gathered from other sources. Either way, your sarcasm is warranted and I welcome the humor! :naughty: While you are correct in principle, you are forgetting to mention is that the ECU is programmed to achieve near perfect "stoich" (i.e., 14.7:1 air/fuel mixture as you stated above) by utilizing incoming and outgoing oxygen at multiple times per second (virtually in real time), and since the ECU is constantly trying to achieve the ideal mixture for complete combustion, the fuel trim is dynamically adjusted, and in the case of warmer air, fuel consumption is reduced.

Yes, I find a nice sense of humour makes things quite an enjoyable entertaining read.
Your Mass Air Flow(MAF) meter actually compensates for warmer air(air weighs less when it is heated) by retarding ignition timing and as the engine is a dynamic air pump, the cylinder is not as 'filled' when the piston is at top dead centre. As ignition timing is retarded so that knock is not introduced, not all of the air:fuel mixture is burnt due to incomplete combustion so your essentially pushing unburnt fuel out your exhaust valves :( This obviously means that engine efficiency is reduced, meaning less torque. As you require a set amount of engine torque to keep the vehicle at a constant speed(to offset tyre/wind drag, etc) then you need to open the throttle body more to give the engine more air flow and thus more fuel. A colder intake air charge means that less throttle is required as more oxygen molecules can be sucked in. Thus, if you compare the MAF voltages to maintain the same amount of applied torque, the voltages would be the same. The only difference is in the ignition timing tables, where the colder intake air will take a few degrees more timing and thus burn all of the injected fuel. If you were to use your Scangauge to measure injector pulsewidth between two different intake temperatures, you will see what I mean ;)

Again, the above is what I am refering to in relation to volumetric efficiency :) Heated air requires more air to make the same amount of torque, with the reduced timing you require even more fuel:air mixture to make the same amount of torque. For example, if cold air required 10 oxygen molecules (147 fuel molecules) to produce X amount of torque, then you would require more oxygen and fuel molecules to offset the retarded timing to produce the same amount of torque BUT the O2 sensor still reads the same Air:Fuel ratio but not how much of it is being passed, which is the key ;) Hence, fuel economy suffers due to warmer intake temps. This can also be seen where car manufacturers suck air into the air filter from somewhere that gets a cold air, usually from the inner wheel arch, over the radiator or from behind a headlight. Essentially, cold air produces more torque as it is more knock resistant.

You're correct, and it's my fault for not addressing this issue. You can also utilize your ideal torque range to figure out the ideal RPM range for most efficient acceleration. A scangauge can really help with this since you can view both real-time fuel consumption and cumulative fuel economy simultaneously. Also, your ECU description partially addresses my last point above.

See above :)

This is correct if you assume that the engine has already reached optimal operating temperature. A significant problem with cold air is that it reduces the amount of time it takes for your engine to warm up to optimal temps, and your ECU compensates by running a rich mixture until then engine has reached optimal temps. What you are probably referring to is a cold-air intake, which can theoretically pull "colder" air by being positioned lower in the engine bay and through insulation from the radiating heat of the motor itself. If we assume relatively warm outside (ambient) air temps, then I believe a cold-air intake can be very effective. The other issue with cold-air intakes is they typically increase the "flow-rate" of oxygen into the throttle body; the MAF sends this information to the ECU, which compensates by adding more fuel to the mixture. Under full-throttle conditions, a cold-air intake will ultimately result in more fuel consumed for that period of time compared to a stock air intake system; however, you can offset this consumption by utilizing the extra power and torque as you've mentioned to maintain a constant cruise speed more efficiently.

Cold air really has no bearing on warming up the engine coolant or engine oil though, especially on a fuel injected vehicle. Old carburettors yes, but fuel injection no :) When the coolant temp sensor is registering a cold temperature, it adds a small percentage of fuel BUT also increases ignition timing so that the the fuel burns hotter to warm the engine sooner. Warm air retards timing but adds the same amount of fuel taking the engine longer to reach operating temperature. On a carby, the engine usually had a Y pipe with a valve connected to the choke, so that during cold starts, the engine would suck air off the exhaust manifold to warm the engine up as they had no way of altering the distributor ignition curve to compensate for the excess fuel. As for the effects of 'ram air' oxygen, the throttle body is a more than suitable restriction to flow. The volume of air required to reduce manifold vacuum is also not apparent to above 100MPH.

I have not, but that is a very interesting example. I am assuming that this data you provided applies to an engine that has already reached optimal operating temperature. This does a good job of showing the ideal load/rpm combination. What vehicle was this data taken from? It would also be interesting to see air intake temps as a function of load and the percent differences from the ideal stoich mixture.

This was from the V6 Pulsar I own/tuned but I also have the program to adjust the ECU in your car(you have a SR20DE motor correct?) There is complete adjustment available of cold start enrichment maps, cold start timing advance, idle speed and other factory maps, all fully tuneable :) You can even set the O2 sensor voltage that you wish the ECU to consider stoich :)

Wow, that is actually quite lean. Under what conditions are you achieving 15.3 AFR? I would assume very low load and low rpm that is near the peak of your torque curve. According to the numbers you just showed on that chart, the highest AFR I calculated was 15.05. Either way, I don't think your ECU could manage 15.3 for very long but I could be wrong. How many pounds of boost are you running?

15.3 was in the twin turbo V8, which uses different software to the screenshot I posted. The software is known as 'EfilLive' and lean fuel figures are considered quite safe with the appropriate tuning tables. 15.3 is its cruise target AFR setting and the rpm is under 2000rpm at highway cruising speeds. My TT V8 is the same car you got over there known as the Pontiac GTO but is the Australian Sports Truck version :grinyes:
To give you an example of what I consider to be fuel economy techniques in conjunction with the tune in the factory ECU. I have light weight billet alloy Boyd Conddington wheels as they require less inertia to maintain momentum, the diff ratio is 3.08:1 to allow the engine rpm to sit below 2000rpm at cruising speeds and with V8 torque levels, it is happy to idle along with minimal load/throttle.
If you think 15.3 AFR's are good, have a look online for the Honda D15B E-VTEC engine, it safely runs up to 19:1 AFR's :smokin:

And unfortunately this vehicle probably won't be 50-state legal due to NOx emissions. :disappoin It would be nice to see more 4-cyl turbo diesel cars here in the US.

Its a shame you guys are not getting it, won numerous awards across the world :) Google i30 and you will see what I mean.

I like how you keep your highway speeds relatively low. :grinyes: This helps reduce the losses associated with aerodynamic drag. Do you practice any hypermiling techniques?

Actually, that is the speed limit over here :disappoin I have plenty of aerodynamic drag as the work gear in the back is usually on a shrink wrapped pallet.
I actually like to be out in front so no hypermilling used, I usually overtake everyone in front of me so I dont get held up behind slower traffic. Most of our roads are single lane in each direction :(
Heres a pic:
http://i252.photobucket.com/albums/hh40/iamhappy46/The%20ute/IMG_7745.jpg

Let me know if you have any other questions :)

Let me know if you have any other questions :)

I probably will in the near future, but that was quite an elaborate explanation. Thanks so much for taking your valuable time to share your expertise, and I didn't realize you were outside of the US! :biggrin:

By the way, that V8 TT you have looks like a modern day version of GM's old El Camino. It's nice to see you investing in American muscle technology and making it into a fuel sipping machine; I wish GM and the other big auto companies out were would wake up and realize they could offer safe and reliable options to consumers to achieve the same results as you have. And diesel technology is definitely the way to go; just image what we could do with hybrid-electric-diesel technology, 100mpgs will soon be old news after that point. One question before I log off here, were those MPG figures converted from kilometers per liter to miles per gallon? I know that the UK uses what's called imperial gallons, which is slightly more than US gallons, but not sure if that's what the Aussies use; my guess is liters, but could be wrong. Good day to you! :grinyes:

Yes, we use litres but I converted from our litres and kilometres to the USA MPG calibrations. I am on a few forums with US members so I have to think in both :)

The TT V8 is running up to 12 pounds on boost and has around 800FtLbs of torque available from 2000rpm to the rev limiter. Also, if you look at the intercooler hanging out of the front of the car, there is a little additional wedge shape welded to the intercooler at the bottom? When I go racing with the car, that tank is filled with dry ice to chill the intake temperatures to below freezing for better volumetric efficiency :)

Test drive a new Pontiac G8, it is the latest sedan version of my ute(The Pontiac G8 ST is due there soon too) Known as the VE Commodore over here, they have won numerous awards and have beaten BMW 3 and 5 series, along with many other luxury cars. Fuel economy with a decent ECU tune gives outstanding results :)

Yes, we use litres but I converted from our litres and kilometres to the USA MPG calibrations. I am on a few forums with US members so I have to think in both :)

Ok just checking because those MPG numbers look ridiculously high considering the engine displacements you are utilizing for both vehicles. You realize that right? Half that amount (25 MPG for the 5.7L V8 and 30 MPG for the 3.5L V6) would sound more reasonable. To better gauge the accuracy of your MPG estimates, could you provide me with an approximate value of gallons per hour that is achieved during a warm-engine idle (when in gear) and a warm-engine cruise at 60 MPH (on a flat, level highway) for at least 1 of your vehicles? This assumes you have the instrumentation to measure this.

The TT V8 is running up to 12 pounds on boost and has around 800FtLbs of torque available from 2000rpm to the rev limiter. Also, if you look at the intercooler hanging out of the front of the car, there is a little additional wedge shape welded to the intercooler at the bottom? When I go racing with the car, that tank is filled with dry ice to chill the intake temperatures to below freezing for better volumetric efficiency :)

I read earlier that your turbo adds 600 ft-lbs of torque, which means that your engine only pushes about 200 ft-lbs shortly before you reach 2000 RPM, so let's just conservatively say 1900 RPM. 200 ft-lbs seems quite small for a stock 5.7 L V8, let alone considering all of the exhaust and header options you've provided for the vehicle, but maybe this is because you reduced the compression ratio to accommodate the turbo, which resulted in a loss of torque and power below 2000 RPMs. Without looking at GM specs, I would venture to guess that the stock 5.7L LS1 engine should push at least 250 lb-ft of torque near 1900 RPM, but you would know better than I. :naughty:

Test drive a new Pontiac G8, it is the latest sedan version of my ute(The Pontiac G8 ST is due there soon too) Known as the VE Commodore over here, they have won numerous awards and have beaten BMW 3 and 5 series, along with many other luxury cars. Fuel economy with a decent ECU tune gives outstanding results :)

Just curious, what is the stock MPG rating of your VE commodore?

Ok just checking because those MPG numbers look ridiculously high considering the engine displacements you are utilizing for both vehicles. You realize that right? Half that amount (25 MPG for the 5.7L V8 and 30 MPG for the 3.5L V6) would sound more reasonable. To better gauge the accuracy of your MPG estimates, could you provide me with an approximate value of gallons per hour that is achieved during a warm-engine idle (when in gear) and a warm-engine cruise at 60 MPH (on a flat, level highway) for at least 1 of your vehicles? This assumes you have the instrumentation to measure this.

I keep full records on fuel usage in litres per kilometre for the TT V8 as it is a work delivery vehicle and comes in handy for tax deductions. I average around 820Kilometres to refill 47 litres, which comes in handy when I get 53 cents in the dollar back for fuel(around AUS$440) and only need to spend $75 filling up the tank plus car maintenance costs. The Pulsar uses the same calculation methods.

I read earlier that your turbo adds 600 ft-lbs of torque, which means that your engine only pushes about 200 ft-lbs shortly before you reach 2000 RPM, so let's just conservatively say 1900 RPM. 200 ft-lbs seems quite small for a stock 5.7 L V8, let alone considering all of the exhaust and header options you've provided for the vehicle, but maybe this is because you reduced the compression ratio to accommodate the turbo, which resulted in a loss of torque and power below 2000 RPMs. Without looking at GM specs, I would venture to guess that the stock 5.7L LS1 engine should push at least 250 lb-ft of torque near 1900 RPM, but you would know better than I. :naughty:

It does not 'add' 600FtLbs of torque but provides more than 600Ftlbs of total crankshaft torque with less than 40% throttle angle. Anything more than 60% throttle is a little scary to drive :runaround: Factory torque rating is 300Ftlbs but considering we are only adding 7psi of manifold pressure, to have more than 100% additional torque available with a 50% increase in air flow is quite good :) 800Ftlbs comes into play when boost controller is raised to 8.5psi :grinyes: The factory torque rating is also listed at 4400rpm but below 3000rpm the stock torque output is pathetic, so to have such a wide band of torque across the rpm range makes it much easier to drive now. The benefits of better fuel combustion :)

I actually INCREASED the compression ratio(10.3 to 10.5) by fitting a slightly thinner 'multi layer steel' headgasket which is why it runs better off boost and less boost is required to make more power. As you would know, Hp = ftlbs x rpm / 5252 :)

Just curious, what is the stock MPG rating of your VE commodore?

Stock it is terrible(check the Pontiac website) but nothing a good ECU recalibration wont fix :)

While I am here, consider that the colder the air the less detonation/knock resistant it is, correct? So more ignition timing allows more of the fuel to ignite and therefore use more of the fuels 'calories' to push down the piston, which results in more torque.
To produce the same amount of torque with warm air, requires more fuel and air to offset the retarded ignition timing which is not releasing all of the energy from the fuel consumed. Thus more throttle is required with warm air, to consume a larger volume of air:fuel as the retarded ignition timing does not release all of the 'calories' from the fuel.
This concept can also be seen in E85 and LPG tuning, where due to the lower calorific rating of these two fuels, more fuel is required to produce the same amount of torque and burn stoich.

I keep full records on fuel usage in litres per kilometre for the TT V8 as it is a work delivery vehicle and comes in handy for tax deductions. I average around 820Kilometres to refill 47 litres, which comes in handy when I get 53 cents in the dollar back for fuel(around AUS$440) and only need to spend $75 filling up the tank plus car maintenance costs. The Pulsar uses the same calculation methods.

Ok, I thought maybe you had the capability of checking your real-time fuel economy, but I guess not. Given the numbers you've just provided for your tank average fuel economy, here's what I got when I did the math: 820km/47L * 3.785L/1Gal * 1Mi/1.62km = 40.76 Mi/Gal

This is more than 9 MPG lower than your original calculation, so I'm not sure what happened. Note, that is the correct conversion if you assume liquid US gallons. What you most likely used to convert was UK gallons (4.55L/1UKGal), which would bring you to 49 MPG based on UK (Imperial) gallons.

It does not 'add' 600FtLbs of torque but provides more than 600Ftlbs of total crankshaft torque with less than 40% throttle angle. Anything more than 60% throttle is a little scary to drive :runaround: Factory torque rating is 300Ftlbs but considering we are only adding 7psi of manifold pressure, to have more than 100% additional torque available with a 50% increase in air flow is quite good :) 800Ftlbs comes into play when boost controller is raised to 8.5psi :grinyes: The factory torque rating is also listed at 4400rpm but below 3000rpm the stock torque output is pathetic, so to have such a wide band of torque across the rpm range makes it much easier to drive now. The benefits of better fuel combustion :)

That sounds about right, but those torque gains are still quite impressive. It would be nice to get some input from some other gear-heads (grease monkeys) in here. :licka:

I actually INCREASED the compression ratio(10.3 to 10.5) by fitting a slightly thinner 'multi layer steel' headgasket which is why it runs better off boost and less boost is required to make more power. As you would know, Hp = ftlbs x rpm / 5252 :)

You must have a lot of faith in your pistons and rings. That's a lot of stock compression, let alone the extra compression that results from the boost you are adding. You definitely can't get away with running anything less than 92 octane gas, that's for sure. The safer route would be to reduce stock compression, but you obviously know what you are doing because you haven't blown your engine yet. :lol2:

While I am here, consider that the colder the air the less detonation/knock resistant it is, correct? So more ignition timing allows more of the fuel to ignite and therefore use more of the fuels 'calories' to push down the piston, which results in more torque.

That's correct, because the higher density of colder air increases the compression, which reduces the resistance to knock. But too much advanced timing could result in detonation, so you have to carefully regulate how much you add. However, regardless of the intake temperature, a properly calibrated ECU (assume the engine has reached warm operation) will dynamically adjust the timing in order to achieve complete combustion such that all of the fuel's energy is pushing the piston at the proper time during the stroke. But as you've already made this point several times, the colder air results in greater volumetric efficiency (not necessarily correlated with thermal efficiency though, so this is important to differentiate), which coupled with the proper AFR and timing produces more torque/power than the equivalent scenario with warmer air.

So the point I'm trying to make is that regardless of what the air intake temperature is, as long as the ECU and timing is well calibrated, your engine should still achieve a complete combustion with near 100% volumetric efficiency when at the most optimal RPM. As a side note, we should remember that it is forced induction that generally yields volumetric efficiencies greater than 100%, so the above assumption I make is regarding naturally aspirated engines.

To produce the same amount of torque with warm air, requires more fuel and air to offset the retarded ignition timing which is not releasing all of the energy from the fuel consumed. Thus more throttle is required with warm air, to consume a larger volume of air:fuel as the retarded ignition timing does not release all of the 'calories' from the fuel.
This concept can also be seen in E85 and LPG tuning, where due to the lower calorific rating of these two fuels, more fuel is required to produce the same amount of torque and burn stoich.

I'm not sure why you are assuming that the ignition timing is automatically retarded during warm air, unless maybe your timing is not properly mapped within your ECU; or maybe I am missing some fundamental issue where warmer air must have a lower timing advance to achieve the same result? I will test this just for you. I will do a morning simulation of timing vs. load and compare that to an afternoon simulation of timing vs. load. The air intake temperature difference will be around 15 degrees F. If my ECU does its job, the timing should almost be identical for the same load, at least this is my hypothesis. I will post my results as soon as I get them. :)

During your test, if you can also measure throttle percentage in relation to ignition timing as well :)

During your test, if you can also measure throttle percentage in relation to ignition timing as well :)

I can do that, no problem. Before I begin recording data, I will also ensure my water temps are at least 168 deg F, which will be my baseline operating temp.

I used my video recorder to ensure the quality and consistency of my data. Here are the results from my first test. Test condition:
1) Neutral Engine Rev, not in gear, vehicle is parked.
1) Air Intake Temp = 150 Deg F
2) Water Temperature = 198 Deg F

Timing Load Throttle Percentage
20 19 0
27 22 2
32 23 3
37 21 4
40 21 5
46 23 7

For the next test, I popped open my hood to let my intake temps cool off some. I placed a small bag of ice cubes near the opening of the air inlet so that as the engine was running it would suck in cooler air. Here's the results from the second test:

1) Neutral Engine Rev, not in gear, vehicle parked
2) Air Intake Temp = 120 Deg F
3) Water Temp = 177 Deg F

Timing Load Throttle Percentage
18 19 0
26 19 1
30 21 2
34 23 3
37 21 4
43 21 5
46 22 6

Note, at 7% Throttle the Engine was near 3000 RPM. Considering the extremely warm intake temperature from the first test, I would have thought (based upon your logic) that my timing would be well below 20 (which would have been retarded by definition), but as I predicted, my ECU was able to keep even my idle speed timing right at 20 deg ATDC, which is near perfect timing. What we also see is a linear increase of timing as TPS is increasing, however since the transmission is not engaged, the load is practically flat-lined.

We see similar results for the second test, where the intake temperatures averaged at least 30 Degrees F cooler than the first test (this difference is quite significant). In fact, when comparing idle speed where TPS is 0, the timing is actually 2 degrees more retarded during the cold air test as opposed to the warm air test; FYI, the timing during TPS = 0 was observed for about 10 seconds, and fluctuated between 16 and 18 deg ATDC, so I just took the higher estimate. The timings for the "cold air" test are only slightly greater than the "warm air" test when comparing similar Load and TPS.

So at this point, with this very limited amount of data, my hypothesis is looking good. :naughty:

Except for one small problem... you realise that the engine fires the spark plugs BTDC, not ATDC ;) So the bigger the timing figure the better, smaller values are retarded timing. Firing the spark plug later means that the igniting fuel does not fully combust before it reaches TDC and thus less energy is released. Then by firing the spark plug earlier before TDC(ie more ignition advance) the fuel is able to completely combust and then force the cylinder down after it reaches TDC. Detonation/knock occurs when the fuel ignites too early(hot spark plug tip, hot intake air, too much compression, etc) and tries to push the piston down BEFORE it reaches TDC, which is a mechanical issue. This is where conrods bend from the force.

Thus, your engine require less throttle to have more ignition timing advance with less load recorded :D Therefore more torque/effort can be created by more ignition timing advance(bigger number) with cooler intake temps.

For example, my Pulsar which uses the 350Z motor:
http://i252.photobucket.com/albums/hh40/iamhappy46/SSS35L/VQ35_timing.jpg

Oops, you are definitely correct, it is BTDC! You didn't really address the results of my data. What's your opinion?

On your chart you provided (thanks for providing this), what variable is represented by the Y-axis?

Ok, I thought maybe you had the capability of checking your real-time fuel economy, but I guess not. Given the numbers you've just provided for your tank average fuel economy, here's what I got when I did the math: 820km/47L * 3.785L/1Gal * 1Mi/1.62km = 40.76 Mi/Gal

This is more than 9 MPG lower than your original calculation, so I'm not sure what happened. Note, that is the correct conversion if you assume liquid US gallons. What you most likely used to convert was UK gallons (4.55L/1UKGal), which would bring you to 49 MPG based on UK (Imperial) gallons.

Those readings are taken with the extra weight of my work gear in the back, so remove the 2200Lbs of work gear and you can see how my 50+MPG figures occur as per original post of 3000Lb chassis(which is actually 3400Lbs)
Sorry for the confusion :)

That sounds about right, but those torque gains are still quite impressive. It would be nice to get some input from some other gear-heads (grease monkeys) in here. :licka:

Keeping in mind that most 'buried' camshaft V8 with pushrods have a peak of around 85% volumetric efficiency, getting boost into them is one good way of increasing torque :) Give me a good DOHC 4 or 6 cylinder with their typical 90% volumetric effiency, then I can get some good figures out of them :)

You must have a lot of faith in your pistons and rings. That's a lot of stock compression, let alone the extra compression that results from the boost you are adding. You definitely can't get away with running anything less than 92 octane gas, that's for sure. The safer route would be to reduce stock compression, but you obviously know what you are doing because you haven't blown your engine yet. :lol2:

We have 98RON gas here, equivalent to your 93. That is why i am running relative low boost, although I have run 12psi boost every now and then for a bit of fun ;)

That's correct, because the higher density of colder air increases the compression, which reduces the resistance to knock. But too much advanced timing could result in detonation, so you have to carefully regulate how much you add. However, regardless of the intake temperature, a properly calibrated ECU (assume the engine has reached warm operation) will dynamically adjust the timing in order to achieve complete combustion such that all of the fuel's energy is pushing the piston at the proper time during the stroke. But as you've already made this point several times, the colder air results in greater volumetric efficiency (not necessarily correlated with thermal efficiency though, so this is important to differentiate), which coupled with the proper AFR and timing produces more torque/power than the equivalent scenario with warmer air.

As you need to ingest more warm air and fuel to produce the same amount of torque, the retarded timing is caused by the throttlebody being open further to get the same amount of oxygen into the motor(more than colder air) and as such, more fuel is injected for the additional oxygen as some of it will not be burnt due to incomplete combustion with the side effect being that extra fuel helps cool the exhaust valves on the exhuast stroke :) This is to help prevent pre-ignition from a hot exhaust valve.

So the point I'm trying to make is that regardless of what the air intake temperature is, as long as the ECU and timing is well calibrated, your engine should still achieve a complete combustion with near 100% volumetric efficiency when at the most optimal RPM. As a side note, we should remember that it is forced induction that generally yields volumetric efficiencies greater than 100%, so the above assumption I make is regarding naturally aspirated engines.

The typical modern engine does not have 100% volumetric effiency unfortunately, due to the wide rpm band that the camshafts must cater for. This is why technology such as Honda's VTEC, Nissan NEO VVL, Mitsubishi Mivec and Toyotas VVTi-L has been developed. Sedate idle, good midrange torque and extreme top end power :)

I'm not sure why you are assuming that the ignition timing is automatically retarded during warm air, unless maybe your timing is not properly mapped within your ECU; or maybe I am missing some fundamental issue where warmer air must have a lower timing advance to achieve the same result? I will test this just for you. I will do a morning simulation of timing vs. load and compare that to an afternoon simulation of timing vs. load. The air intake temperature difference will be around 15 degrees F. If my ECU does its job, the timing should almost be identical for the same load, at least this is my hypothesis. I will post my results as soon as I get them. :)

As you require a certain amount of fuel mass to create torque, the engine needs to suck in more warm air which requires more throttle. The TPS sensor talks to the ECU and when the air flow meter calculates its air flow figure multiplier, it alters the position of the cells being referenced in the fuel and timing maps. This is one reason why my V6 Pulsar(B13 chassis) gets such good fuel economy. I can actually watch in real time which cells are being accessed, warmer air will move the fuel map up one cell and the timing map down one cell, there is some interpolation depending on the difference in values. Unfortunately, the standard ECU calibrations are usually far from perfect due various reasons.

As you have now seen, more timing with coler intake temps when under load means more efficient combustion :) AFR targets are good 'guide' but if your passing more air and fuel through the motor due to incomplete combustion for the same amount of torque, the AFR readings will be the same but more 'flow' has occured with warm air. This can be seen by going on ebay and searching for 'CAI' and reflects the aftermarket industry obsession with getting the coldest air for more power(and hence torque)

Oops, you are definitely correct, it is BTDC! You didn't really address the results of my data. What's your opinion?

On your chart you provided (thanks for providing this), what variable is represented by the Y-axis?

Sorry, I not had much time to reply as yet. I am about to get dinner and will reply next time.

The Y axis is the throttle position + air flow meter multiplier :)

http://i252.photobucket.com/albums/hh40/iamhappy46/iat_calibration.jpg
Here is the Intake Air Temp Sensor calibration in the V8. It is in celcius but it indicates how much retard occurs under normal driving conditions :)

Wow, that's a lot of extra weight. Still, a 40 MPG average with all of that weight is quite impressive. Good work! :)

I guess I am gradually starting to understand how higher temperatures result in a more retarded timing, particularly under heavy load this would make sense. Unfortunately my test was under low-load conditions, so it would most likely be safe to say that higher verses lower air-intake temperatures don't matter as much during low-load operation.

Also, when I was referring to volumetric efficiency, I stated "near" 100% (not exactly this much) and stated that this efficiency peaks during warm engine operation at a moderate load (say 40%, but this is merely a guess). Since my engine is DOHC, I would venture to guess my volumetric efficiency is somewhere in the high 80s or low 90s, of course this would depend on load, operating temps, and air intake temps.

Without doing the math on this, I would venture to guesstimate that the volumetric efficiency gained by using a modified cold-air intake is equivocally if not more-so dependent on the high-flow characteristics of the air-filter element that is commonly used in these types of devices; the higher density charge of oxygen is important, but I would argue that the "breathability" of the air filter itself, coupled with an appropriately tuned exhaust system has just as much if not a greater importance in volumetric efficiency. Would you agree?

By the way, what is grams/cylinder? Is this the air-fuel mixture expressed in terms of mass? Also, what do all of the negative numbers mean in the main body of the chart?

The benefits of more torque in the V8 is at low rpm, I am running less engine revolutions at cruising speeds due to a high 3.08 diff ratio, so even less fuel is required :) My Pulsar happily sits on 2200rpm at 60mph and the V8 around 1600rpm depending on whether the stall converter lockup is engaged.

I can see how your looking at it from a scientific point of view but the mechanics of it is the variable. Heavy load does make a difference as AFR's drop into the 12:1 area, as I believe your car has the Nissan SR20DE 2L motor, I can confirm that it actually dips into the 11.3:1 range under high load :( On a standard ECU calibration, the timing cells have massive variances between them which allows the engine some protection from driver abuse.

Your engine in standard form is around 90% in stock form, basic breathing modifications can bring that up to 93%. The ebay CAI 'nasties' are good for making extra power due to the high flow nature of the filter BUT by position them in a colder area of the engine bay with a colad air feed, there is more 'mass' of air. Thus, the freer flowing filter is required to draw in the 'thicker' air. There is a few upgrades to the standard air filter than can be done though, I actually have used the standard air box on my Pulsar with great results by running a 2.5" flexible rubber pipe from inside the inner wheel arch behind the bumper bar and feeding it into the factory airbox. As you stated though, the engines breathing is very important. By allowing fresh cold air into the motor, it can combust more completely and the higher temps allow the exhaust manifold vacuum to scavenge more exhaust gas from the cylinder, making it even more efficient :)

Grams/Cyl is the axis used when using a Manifold Air Pressure(MAP) sensor instead of a Mass Air Flow(MAF) meter, which directly relates how much the cylinder of a given capacity is 'filled'. With more temperature but similiar 'mass' from the same amount of air:fuel being drawn in, it retards timing by x amount. If you look at the left hand side column, you will also note the additional timing tables on offer. A much more complex system in this car.

I should have some time later this week to post a few screen shots of your ECU calibration if your interested :cool:

I can see how your looking at it from a scientific point of view but the mechanics of it is the variable. Heavy load does make a difference as AFR's drop into the 12:1 area, as I believe your car has the Nissan SR20DE 2L motor, I can confirm that it actually dips into the 11.3:1 range under high load :( On a standard ECU calibration, the timing cells have massive variances between them which allows the engine some protection from driver abuse.

Actually I have the KA24DE 2.4 L motor, which is very different from the SR20, where the KA has a lot more low-end torque and a wider torque curve and the SR has a higher redline and a shorter stroke, allowing for more power but less torque on the low-end. The KA was actually designed for Nissan's small pick-up trucks like the Frontier and was also used in the XTerra. Unfortunately, the motor is mated to a wimpy 4-speed auto tranny, and my fuel economy tends to suffer when I go faster than 60 mph (mainly a result of a less than ideal axle ratio of 4.09); my 4th gear is .69. I'm not sure how this would influence my AFR's, but based upon my description, you could probably get an idea.

Your engine in standard form is around 90% in stock form, basic breathing modifications can bring that up to 93%. The ebay CAI 'nasties' are good for making extra power due to the high flow nature of the filter BUT by position them in a colder area of the engine bay with a colad air feed, there is more 'mass' of air. Thus, the freer flowing filter is required to draw in the 'thicker' air. There is a few upgrades to the standard air filter than can be done though, I actually have used the standard air box on my Pulsar with great results by running a 2.5" flexible rubber pipe from inside the inner wheel arch behind the bumper bar and feeding it into the factory airbox. As you stated though, the engines breathing is very important. By allowing fresh cold air into the motor, it can combust more completely and the higher temps allow the exhaust manifold vacuum to scavenge more exhaust gas from the cylinder, making it even more efficient :)

I plan to keep it stock, except for the K&N drop-in air filter which does provide better breathing. Maybe I could substitute a nice and thick, flexible rubber hose in place of my relatively thin plastic hose which could potentially provide better thermal insulation from my motor; I may even be able to fabricate a metalic heat shield to reflect some of that heat back toward the motor and away from my air intake.

I should have some time later this week to post a few screen shots of your ECU calibration if your interested :cool:

That would be great, except remember that I have the KA24DE, not the SR20. :biggrin:

KA24DE Primary Ignition timing calibration :)
http://i252.photobucket.com/albums/hh40/iamhappy46/KA24DE_ign.jpg
Based on your cold temperature from previous page, load cell 21 with 5% throttle has 43 degrees timing value around 3000rpm. You can see how much cell variance is required to get to the warm air ignition timing cell value... The green values are when the ECU is listening to the knock sensor, so warm air can even retard timing further depending on any valvetrain noise, etc.

We also get the KA24 here in the U12 chassis shape but we have the USDM KA24DE tune for the Altima and 240SX available, which is the tune I added above :)

Nice work! :grinno:

I wish I had the software to generate all that stuff! :tongue:

Luckily, the software is freeware ;) Buying the hardware to modify and load the new program is not free though but it is reasonably priced.

However, the software alone should give you a good idea of how your ECU calibration works and how it could further improve your fuel economy :D

Luckily, the software is freeware ;) Buying the hardware to modify and load the new program is not free though but it is reasonably priced.

However, the software alone should give you a good idea of how your ECU calibration works and how it could further improve your fuel economy :D

So what can you offer for mods to help my '00 altima to get better gas mileage?

I am a pizza delivery driver, and I know this affects my gas mileage very much. I do have the ability to keep my car under 2k rpm's and still go pretty fast from a stand still to 40mph. I always use the pedal to shift the car into the next gear by habit. Hey, I'm weird, gimme a break.

Anyways, how do I get more torque?

One of the easiest modifications is advancing the base ignition timing by 2 or 3 degrees if your prepared to run a strict diet of higher octane fuel. This can be achieved by advancing the crank angle sensor(the distributor) timing. This will increase torque via advanced ignition timing across the whole rpm range but more importantly, still have the factory ECU 'protection' strategies in place if you do get a bad batch of fuel.

As above, a cold air intake system of some kind will allow more ignition timing with less fuel and air being ingested by the engine to make the same amount of required torque.

That would be my first two fuel economy based modifications of choice.

I am a die hard I wanna learn how to do it myself fan, so if you could tell me how to do the first one, then I can learn it for myself :D How do I do that? Thanks.