Aftermarket intakes & exhaust for economy?

[rob47v]

Well I've been curious, I know better intake and exhaust will let the engines breath better but with a better breathing engine without any other mods. Will it provide more fuel economy? I know the intake and exhaust ports should not be touched cause it disturbs the flowing characteristics of the motor thats on the head side but what about prior to the head will it help?

[maximilian]

K&N advertises their intake stuff gives more hp, which I imagine would translate to better fuel economy with the same driving habits.

[theholycow]

I have strong doubts about aftermarket intakes/exhausts helping fuel economy for anyone who doesn't drive like Mario Andretti. Here's why: The intake and exhaust need to be able to flow freely enough to move all the huge amount of air required when WOT at redline, making the most power the engine can make. If it can do that, then logically it should be entirely free of obstruction when making the relatively small amount of power that economy-minded drivers use daily.

There is a link in my sig to a recent thread about exhaust upgrades where interesting ideas supporting the use of aftermarket exhaust are presented, though I remain doubtful. In my "Meta-Sig", there's a link about intakes.

[maximilian]

Just the excuse I was looking for not to upgrade! Thanks!

[ericgrau]

on my 2005 ford focus with 2.0 duratec engine I was averaging 29.5mpg commuting to work. I took out the lifetime airfilter (that was a joke) and Put on a K&n setup. Then my average fuel economy went up to 33.5. I swear by it so much that I WILL be getting the same setup for my newer 2007 Ford Focus.

[maximilian]

Drat! Back to where I started.

[Biffmeistro]

Going towards freeing up restrictions is good such as getting a less baffled muffler, high flow catalytic converters, and higher flow air filters. However going towards a larger diameter intake or exhaust tubing is bad.

The smaller diameter intake/exhaust leads itself far better to low end torque (and low end efficiency) then a larger diameter. With the small amount of air that you flow when at low RPM, the smaller diameter has a much higher intake air velocity, so you'd have a better mix and a better volumetric efficiency. The smaller exhaust also leads to a faster flowing exhaust gasses, which help suck air out of the combustion chamber when the exhaust valve is opened, leading to less pumping losses, despite the greater back pressure.

Age old tuning wisdom:
Smaller diameter = Low end torque
Larger diameter = High end horsepower

By all means get a better air filter, or a better muffler, or a high flow cat... But don't go for aftermarket intakes/exhausts that advertise "More Horsepower!" They'll just give you more in the top end, and lower your output in the low end.

Edit: If you want, definately get an aftermarket intake/exhaust tuned for low end torque. Good headers and mandrel bent exhaust would definately help if it's combined with small diameter pipes.

[krash133]

IMEHO(In my educated honest opinion) Dealing with motors as an air pump if you think about it, if you free up the intake or air (air filter kit) you can get more air into the cylinder, making it fill better and increase torque or V.E.(Volemetric Efficiency), a few more hp might be had as well. A larger or better flowing exhaust will allow the combusted air to move more quickly out of the chamber and in a high rev/high hp where the motor/pump is moving lots of air through and more total hp is made, this is what you want, you sacrifice some ft/lbs low rpmfor a larger power curve and higher engine output at high rpm.

For the basics (my personal experience included), air intakes help mpg(mainly torque gains), exhausts can hurt or negate that low end gain for top end power(not needed in street/mpg uses).

Part of the reason diesels are so good at milage is that they make gobs of torque at low rpm which accelerates mass best not hp numbers......hp is related and important, but more so at higher rpm.