Bolt-ons = less restrictive, Better MPG???
 

So if bolt-ons are less restrictive and in turn allow the engine to produce more horsepower, do they lead to better fuel economy under conservative driving habits?

Can't speak for the 370, but I've had a lot of bolt ons for my other cars, and there is a small improvement. Nothing that you can use to justify buying parts to the wife though :p

Not really true.

The engine is an air pump...

The more air that goes through it, the more fuel that also goes through it to maintain the air-fuel ratio.

Fuel economy is more or less (these days) a function of efficency of the engine and drivetrain (how well heat is translated to movement) and aerodynamics and weight.

There is some potential gain (1-2 mpg in my experience).
If we were to say there was NO gain to be had by an engine breathing better, we would also be saying that it doesnt matter how filthy an air filter gets, it won't affect your gas mileage.

RE: dirty air filter / MPG

I think it's more of a case of the ECU having to compensate with using more fuel for less air (at speed), to prevent a lean (and potential detonation) condition.



The only way to get more power, is to increase the amount of air going through the engine. The only way to make that air to burn and produce power, is to add fuel. Fuel-to-air, is a fixed ratio (relatively speaking, theres only a slight variance...). Therefore, no matter how much air you can get through the engine, with fuel-air ratio and total efficency of the engine's ability to convert fuel-air into real power...your MPG will NOT increase.

Yes.

There was a thread before where this was extensively covered. Theoretically the answer is no because the AFR stays the same. In practice, bolt-ons lean out the car which you could argue means less fuel usage.

In practice, I have all the bolt-ons offered for the 370z and I average around 13 mpg according to my trip computer.

I'm quite happy that my $3,500 in bolt-ons are saving me gas every day, otherwise the difference in my fuel bill would make me go broke because I drive at least 600 miles a month in my Z.

Headers alone(nothing else, no CAI), won't increase MPG?

dad - unless headers somehow tap into free-energy, no.

I've read and have been told the less restriction of the exhaust would increase MPG!-not arguing, just stating.

Guarantee you it will increase MPG if you drive conservatively.

Shifting at lower than normal RPM (since you now have the same amount of power at 2.5k rpm than you used to at 2.7k. As long as you do not BOG your engine or go WOT at low RPM the car should get better MPG.

So this means not driving 70mph on a 55 anymore...go 65mph or 60mph.

CAI in my car upped MPG by like 3 on the highway but it sucked in the city because flooring just felt/sounded soo much better.

Engine braking (fuel shuts off after about 1 second at most when gas pedal is released) your way to stop lights will increase MPG as well. Add 3-5 psi in your tires for less rolling resistance, short ram intakes instead of cold.

Double clutching helps, but rev match seems the better option!
Clutch catching will help MPG...instead of squeezing the meat on your clutch when you shift, have the clutch catch before adding the throttle.

Hard at first but helps alot in the city!

Just my .02cents,

Regis

The real gain in gas mileage tends to be involved with a freer flowing intake, which typically leans out the engine a hair. More intake gains are based on leaning fuel out versus actual air velocity going into the engine. Leaning the fuel out will allow for same throttle position to net more miles per gallon then the stock intake provided.

A lot of us are seeing 18 or so WHP from intakes alone, makes you wonder if the engine really needed the extra air or if a stock 370Z is really really rich..

Hmmm thanks for the fuel lesson! seems quite simple once explained.

maybe the extra air from the intakes is misting/making the fuel leaner?
Maybe pushing the fuel at a higher velocity? That or the ECU is adjusting for the change in air velocity...

makes ya think huh

Well speaking from my experience... I took a road trip in the z before I did anything to it. I got about 25.5-26 mpg... I took the same trip, on the same roads driving the same way I always do, after jwt intakes and berk test pipes.. and averaged 28...

The computer uses a mass air flow sensor in the intake and O2 sensors in the exhaust. It tells it how much air is going into the engine, which then allows the computer to decide how much gas to send in with it. If it is too much fuel, the O2 sensor will detect that it is too rich and decrease the dwell time on the fuel injector to lean the mixture. That way the A/F ratio stays around 12.0:1. This does not make the most power! The best ratio is around 14.0:1 air to gas ratio, but that mixture runs quite hot and you can melt pistons in a performance engine. You can get away with that lean mixture in a Toyota Prius, but not in an angine that can spin 7,500 rpm and make close to 100 hp/liter.

With that said, if youre in 120 degree heat, the air is less dense and the MAF sensor will detect that. It will decrease how much fuel is injected to maintain that 12.0:1 A/F ratio. You'll make less power and use less gas.

If you put headers, exhaust and intakes on your car and gain 40hp, it's because those less restrictive parts are letting more air into the engine. The MAF will sense that and increase how much fuel is injected in order to maintain the 12.0:1 A/F ratio. Then, Viola! More power at the expense of more gas.

If you are getting better gas mileage, it's either because 1) you're making less power. Or 2) your A/F ratio is running leaner than what Nissan wants it to and may be at risk of damaging your engine.

I too learned the addage that headers will decrease backpressure and increase fuel mileage, but that was in the 70's in an era of carburation and restrictive intake/exhaust setups. In those cars, going to a free flowing exhaust would, in fact, lean out the jetting and you would get more power per fuel used because the carburator can't adjust the A/F ratio unless you manually change the jets in it.

Exactly! :)

I noticed when I put on the Berk test pipes my MPGs went up slightly. Also the Berk test pipes are the only mod I have installed so far.

TBH, adding power mods will probably make you drive the car harder than you already do. Which would definitely kill your gas mileage. To answer your original question, I doubt any mods would make much of a difference.

:twocents:

I've already replied to two extensive threads with this exact answer before. I really didnt feel like doing it a third time. Thanks
More power = more air = more fuel...thats what I meant with the tapping into free-energy comment. By definition more power means more energy and that requires more fuel.

The only case I could see maybe a increase of mpg and power is if you got intakes that dont necessarily flow better, but simply trick the MAF sensors to get the ECU to run a leaner mixture. The car would make more power and use less fuel...theoretically.

You could also do this with a simple tune. Lean out the target AFR and voila, more power, less fuel. (More heat --> detonation --> you french fry instead of pizza and have a bad time)

Excellent explanation:tiphat:

Bolts on = wife justification
 

"What happens in my garage stays in my garage"! Yeah, I've notice a small MPG improvement (approx. 0.5 - 1.5 mph) depending on driving conditions - nothing to brag about.