Gas Efficiency

[Gustav832]

I've heard that cold air and short ram air intakes can increase gas mileage, is this true, and if so by how much? Also, which will produce better gas efficiency results. And is it true that short ram is louder?

Also, I've heard headers increase gas mileage, again, is this true and by how much?

And finally would something like this really work, or am I getting screwed if i buy this: http://www.autopartswarehouse.com/pe...00&partid=8443?

PS Any other tips/ parts/ things i could do to up gas mileage is greatly appreciated, I commute over 50 miles a day.

PSS Also if the tornado thing does work, is there any point in getting it if I purchase an intake?

PSSS I did read the post on gasoline, but what is the general consensus concerning buying the higher grade fuels, do they get more gas mileage, and if so is it enough to jusitfy the higher cost?

[Igovert500]

Alot of misconceptions here.

First off let's start with the Tornado. It is a POS. Don't waste your money. If you do a search for 'Tornado' you will find this topic has been beaten to death.

Second, it is a common myth that people seem to believe that higher octane affords you more power or better fuel economy. This is simply not hte case, higher octane has one purpose, to prevent pre-detonation (aka knock).
I would suggest reading this thread, both the first post on the first page, and the last post on the 2nd page.

Another widely repeated myth regarding fuel economy is that intake and exhaust mods will help. A cold air intake's purpose is to bring in cooler air from outside the engine bay. This decrease in temp means more oxygen content in the air. However, when the car's computer (ecu) reads more oxygen, it sends more fuel. So mods like this, while they may add some power, can actually reduce fuel economy. Granted, if they reduce restrictions in the flow of air, then they may in fact help, but this is a secondary effect. As reducing restrictions with these mods is mainly done for more power, and generally if you have more power, you are probably using it, and not driving slowly to conserve gas.

This thread covers this topic pretty well.



Basically, if you want better fuel economy, the trick isn't to spend more money on more expensive gas, or cheap marketing gimmicks, or modifications, but to do the smart free stuff.

a) check your tire pressure, underinflated tires are one of the biggest things people overlook. The lower the pressure, the more friction with the pavement, which has a negative effect on fuel economy

b) driving habits, is the 1st or 2nd biggest thing. Learn to shift lower, accelerate slower, and keep a drive slower (the faster you go, the more power is needed to overcome drag and wind resistance). I drive my sports car hard, average on the highway with my spirited speeding is 360 miles to a tank, I did a fun experiment and did the same highway drive with cruise control set on the speed limit, and the same tank lasted over 550 miles. So yes, driving habits, do have a HUGE impact.

c) turn off AC

d) reduce drag, close windows, remove anything like a stupidly placed pepboys wing that is acting like a parachute on the back of your car (if this applies to you).

e) reduce weight...don't carry a ton of stuff around if you dont need it in the car

You would really be surprised how little power is required to keep your car moving at a steady speed. But the more drag or resistance, which can either be a result of something on your car (wing/low tires/excess weight) or something int he world (hill, headwind) the more power needed, therefore the more fuel. The same applies to what speed you are traveling at...the faster you go, the power necessary multiplies exponentially. This is why you may only need to add 20hp to increase your car's top speed from 110-130, but you will need to increase it a few hundred hp to change the top speed from 180mph to 200mph.

So yeah, bottom line, reduce drag and resistance in any form, and don't waste money on gimmicks.

[KiwiBacon]

Cold air will reduce fuel economy. But through characteristics of the throttled petrol engine.

The throttle in a petrol engine causes large parasitic losses, it reduces the amount of air entering the engine by creating a pressure drop.

Colder (denser) air means the throttle has to be closed further, causing a bigger pressure drop for the engine to suck against which impacts on fuel economy.

Igovert covered well the basic steps to better fuel economy. Bolt ons are BS. If they worked then they'd be standard on new cars.

[bluevp00]

The best mod for increased fuel economy is your right foot.

Acellerate gradually, coast to stops, don't use A/C. You'll learn to fine tune your driving habits after practicing, just keep an eye on your fuel economy calculations to see what works best.

[UncleBob]

take the money you were planning on spending on bolt ons and buy a nice used scooter. 80mpg around town.

Or better yet....buy a bicycle.

There is kiwi said, there is no bolt on hot ticket. No snake oil that you pour in the tank. The only notable option is your driving technique and keeping the car in good shape (tires, engine maintanence etc)

[psychopathicdude]

I used to have a "fuel efficiency gauge" (I think it's in a box in the garage)....it was really just a manifold vacuum gauge, which is a fairly good indication of engine load. Medium vacuum (idle and moderate acceleration) was yellow. High vacuum ( cruise and deceleration) was green. Low vacuum (acceleration or high speeds) was red. You could make your own dial for an off the shelf vacuum gauge. your best fuel economy is when you keep vacuum high, that is: avoid aggressive acceleration, excessive speeding, and unneccessary downshifts. our feet tend to be somewhat imprecise, and we sometimes don't realize how far we have increased throttle. with a gauge to watch, i noticed throttle position a lot more.

and the other stuff....clean out crap, air up tires, keep engine in good shape.
don't fall into the trap of spending more money to save money. Many products brag about "a 5 or 10 % increase in mileage!" Do the math...how much would that really save you? You can increase your mileage that much or more by driving more fuel-consciously. As has been said, if any one product was SO AWESOME, they'd be putting one on at the factory! Manufacturers are under increasing EPA/CARB pressure to make good mileage numbers, don't you think they'd have tornado-like device already in the intake if it helped that much?

[KiwiBacon]

Originally Posted by psychopathicdude

I used to have a "fuel efficiency gauge" (I think it's in a box in the garage)....it was really just a manifold vacuum gauge, which is a fairly good indication of engine load. Medium vacuum (idle and moderate acceleration) was yellow. High vacuum ( cruise and deceleration) was green. Low vacuum (acceleration or high speeds) was red. You could make your own dial for an off the shelf vacuum gauge. your best fuel economy is when you keep vacuum high, that is: avoid aggressive acceleration, excessive speeding, and unneccessary downshifts. our feet tend to be somewhat imprecise, and we sometimes don't realize how far we have increased throttle. with a gauge to watch, i noticed throttle position a lot more.

While a vacuum gauge is a good guide to how far open the throttle is, it's counter intuitive.

A throttle petrol engine is most efficient running very little vacuum. Have a look around for the BSFC map I've posted up.

[Steel]

Originally Posted by KiwiBacon

While a vacuum gauge is a good guide to how far open the throttle is, it's counter intuitive.

A throttle petrol engine is most efficient running very little vacuum. Have a look around for the BSFC map I've posted up.

That's work-efficiency, not fuel mileage efficiency. Brake specific fuel consumption maps merely point out that at x RPM at 100% load your motor will get as much power from the fuel as it can, i.e. its using the fuel efficiently. This does not mean you will get great gas mileage.

The most efficent petrol engines would be quite small engines running very high compression ratios working at top work efficiency. But they probably wouldnt last too long if you're asking them to run at 90% of their top speed constantly. That's why diesels are better in every way.

[KiwiBacon]

Originally Posted by Steel

That's work-efficiency, not fuel mileage efficiency. Brake specific fuel consumption maps merely point out that at x RPM at 100% load your motor will get as much power from the fuel as it can, i.e. its using the fuel efficiently. This does not mean you will get great gas mileage.

The most efficent petrol engines would be quite small engines running very high compression ratios working at top work efficiency. But they probably wouldnt last too long if you're asking them to run at 90% of their top speed constantly. That's why diesels are better in every way.

There is no difference between what you call "work efficiency" and what you call "fuel mileage efficiency".

For example, running a car in 4th gear at 100km/h will give more vacuum than running a car in 5th gear at 100km/h.
5th gear has a wider throttle opening and less vacuum, yet the engine is using less fuel, less air and turning at lower rpms.

If you want to know how much air (and/or fuel) is entering your engine then a vacuum gauge cannot help. You need to read from the air flow meter or fuel computer. Manifold pressure alone is useless.

I agree that a small engine running at higher load will give better efficiency, but not running at the 90% top speed that you claim.
The engine has to be sized to run near maximum load at a speed below peak torque for best BSFC.
Making an engine last while doing this isn't a problem. Convincing the consumer to buy a car with no reserve power will be.

[curtis73]

I love you all, but I'm tired of hearing about "pumping losses". The bottom line is that you need to ingest a certain amount of air (and therefore fuel) to maintain highway speed. The less throttle you have open, the less air is ingested and therefore less fuel.

RPM plays a big factor as well, since the same throttle opening at a higher RPM will suck more air, but STOP TALKING ABOUT PUMPING LOSSES AS A FACTOR IN MPG! I love you all.

[KiwiBacon]

Originally Posted by curtis73

I love you all, but I'm tired of hearing about "pumping losses". The bottom line is that you need to ingest a certain amount of air (and therefore fuel) to maintain highway speed. The less throttle you have open, the less air is ingested and therefore less fuel.

RPM plays a big factor as well, since the same throttle opening at a higher RPM will suck more air, but STOP TALKING ABOUT PUMPING LOSSES AS A FACTOR IN MPG! I love you all.

Okay, I'll won't mention such things in this post.
But only if I can post my favourite picture again.

[Steel]

Originally Posted by KiwiBacon

There is no difference between what you call "work efficiency" and what you call "fuel mileage efficiency".

For example, running a car in 4th gear at 100km/h will give more vacuum than running a car in 5th gear at 100km/h.
5th gear has a wider throttle opening and less vacuum, yet the engine is using less fuel, less air and turning at lower rpms.

If you want to know how much air (and/or fuel) is entering your engine then a vacuum gauge cannot help. You need to read from the air flow meter or fuel computer. Manifold pressure alone is useless.

I agree that a small engine running at higher load will give better efficiency, but not running at the 90% top speed that you claim.
The engine has to be sized to run near maximum load at a speed below peak torque for best BSFC.
Making an engine last while doing this isn't a problem. Convincing the consumer to buy a car with no reserve power will be.

I don't know what kind of car you're driving, but i'f im tootling down the highway in fourth gear, i most definetley have to hold the throttle wider than in fifth gear.

*edit* Anyway, as i said before, your thoughts aobut BSFC does not relate to fuel mileage. Simply put, the best BSFC you'll get is when your at peak torque RPM at WOT. This means you will get the most power per pound of fuel = work efficiency. This does NOT mean you will get better fuel mileage by running at max BSFC, UNLESS you need that amount of power. Anymore and you're wasting gas. Simple as that. Auto's are inherently inefficient because of the range and loads that the engine must go through. Most of the time people only need 80hp to cruise down the highway at 70MPH, so what would be the point of running the engine (v8 for example) at 4000RPM to make 280 pounds of torque and 200 horsepower?
Prime movers on the other hand are designed to go two speeds most of the time, Stop and Go. Go means WOT at torque peak = best BSFC = best fuel efficiency.

[KiwiBacon]

Originally Posted by Steel

I don't know what kind of car you're driving, but i'f im tootling down the highway in fourth gear, i most definetley have to hold the throttle wider than in fifth gear.

*edit* Anyway, as i said before, your thoughts aobut BSFC does not relate to fuel mileage. Simply put, the best BSFC you'll get is when your at peak torque RPM at WOT. This means you will get the most power per pound of fuel = work efficiency. This does NOT mean you will get better fuel mileage by running at max BSFC, UNLESS you need that amount of power. Anymore and you're wasting gas. Simple as that. Auto's are inherently inefficient because of the range and loads that the engine must go through. Most of the time people only need 80hp to cruise down the highway at 70MPH, so what would be the point of running the engine (v8 for example) at 4000RPM to make 280 pounds of torque and 200 horsepower?
Prime movers on the other hand are designed to go two speeds most of the time, Stop and Go. Go means WOT at torque peak = best BSFC = best fuel efficiency.

You should take a long hard look at that graph, it's right above your post and answers all of your concerns.

See those lines that arc through it (the 30kw one is red), they are constant power lines.
If the car with this engine needs 20kW to push it along at cruise, then reading the graph will show that is best acheived at just under 2000rpm and requires approximately 1/2 throttle.
The BSFC at this point is approximately 260g/kwH.

If the same car is geared to run at 3000rpm then to deliver 20kW requires approx 1/3 throttle.
The BSFC at this point is approximately 310g/kwH.

The fuel consumption of this engine at 3000rpm is 20% higher than 2000rpm for the same power output.

[Moppie]

Originally Posted by KiwiBacon

The fuel consumption of this engine at 3000rpm is 20% higher than 2000rpm for the same power output.

Which is exactly what Steel has been saying

I think we're your both getting confused over the issue is how engine RPM and load relate to throttle position.

[KiwiBacon]

Originally Posted by Moppie

Which is exactly what Steel has been saying

I think we're your both getting confused over the issue is how engine RPM and load relate to throttle position.

This is the part I was disagreeing with:

Originally Posted by Steel

as i said before, your thoughts aobut BSFC does not relate to fuel mileage