tcrossley

hello all,

just thought i would share my findings. i have 2002 MP5, auto. has 10,000 miles. I normally get 330-350 miles per tank. 3 weeks ago i purchased a CAI off of ebay. Fit very nice, clean install. drove car, i could not notice any increase in power. the engine was SIGNIFICANTLY lounder (induction "growl").

amazingly, my mileage for 3 tanks of gas was 305,320,310, which is much less than i was getting before i installed this.

i just removed it, reinstalled stock setup. my theroy is that to maintain 70-75MPH on the highway, slightly more throttle is necessary with the CAI installed. the CAI has 3" pipings, the maximum CFM of the 3" is greater, but the VELOCITY of air traveling in it it LESS than the smaller stock setup. the air velocity(speed) is the largely responsible for "filling" the cylinders on the intake stroke.

i'm keeping my stock.

Todd (BMW Mechanic)

leungwingkei

Yup, you're exactly right, same theory applies to exhaust diameter piping.

But I'm not too sure about the fuel mileage part, since when I got my short ram installed, I experienced better fuel economy. Maybe it was due to a dirty stock filter, etc? Perhaps.

And the other reason you may be getting worse fuel economy is because the CAI in cold weather will prompt the ECU to run richer in startups, and also because the ECU is adapting to the new intake. I also noticed really bad fuel economy when I first installed an intake. After 2 tanks it bettered even the stock setup.

ZiO

You should get better mileage because there is better air flow. BUT........BUUUUUUUUTTTTTTT.. if you tend to drive your card hard with the intake, that means MORE air into your engine, resulting in MORE gas as well... resulting in MORE power... so if you have an intake and drive NICELY.. you should notice a slight better mileage increase... this is what i noticed with mine... but when i drove it harder, my car tended to resemble an alcoholic.;

Mach 1

Isnt "BETTER AIR FLOW" the same as "more air into your engine"

In either case, based on your theory, gas mileage should go down, just not in one instance, right?

SlickMp5

So just out of curiosity which cai did you but and can you use it on a manual and if so are you going to sell it and for how much?

JFanaselle

after making and istalling a short-ram on my 1.6, I didn't notice anything different (except for the beautiful sound) for a couple of weeks. After taking a trip to arizona last friday (to pick up some wheels and tires, which look INCREDIBLE on my car), I noticed about 35 more miles per tank.which is a few more miles per gallon. And my car is in desperate need of a tune up (plugs, wires, oil, etc), so I'm sure it'll improve more after that. I stuck with 2" pipe, though (same as stock).

ZiO

Since people like to be smart asses, all I am going to say is learn how to drive if you want good mileage. Thats what it comes down to.

Mach 1

Great response to an intelligent question regarding your previously unknowledgeable post.

Way to go...