Altima Fuel Economy

[methodmix]

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?

[mmcleo11]

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

[methodmix]

Originally Posted by mmcleo11

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.

Originally Posted by mmcleo11

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.

Originally Posted by mmcleo11

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

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

[mmcleo11]

KA24DE Primary Ignition timing calibration

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

[methodmix]

Nice work!

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

[mmcleo11]

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

[Adrenalex]

Originally Posted by mmcleo11

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

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?

[mmcleo11]

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.

[Adrenalex]

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 How do I do that? Thanks.