Personal experience w/ CAI and f/e
 

I know this has been talked about quite a few times. Some people believe that with a cold air intake you will get better MPG and some believe you will get worse. This is my personal expence with one on an '05 Toyota Corolla a/t with an electronic controlled throttle body.

When i was modding for performance (acceleration), i originally bought an AEM short ram intake for my car. Unfortuantely at the time i had the short ram, i never recorded my f/e, so i don't know if it actually helped or not, but i doubt it. I used it for a while, then switched to an Injen cold air intake (CAI). I always thought i was getting better f/e with either of the intakes, but i couldn't know for sure because i started recording tank MPG after i had gotten the CAI. In April '09 i also started driving for f/e after i started recording my fill ups.

In Aug '09, i decided to experiment with my car and installed the stock oem air box in place of the CAI. With the same driving style since April, i was getting at least 1-2 MPG more per tank with the stock air box installed, with a normal paper filter. I've since sold the Injen intake.

My conclusion is that my car gets better fuel economy with the factory installed air box than it does with a cold air intake.

Thanks for the data. That agrees with the standard thinking around here, but it's even better to have solid numbers to back it up.

Thoughts on a higher flow filter in stock configuration?

You can read my experience and many other people's experience with going from a pure hot air to cold air intake on a naturally aspirated volvo 850 here. This is a very common fix on older volvos.
http://www.matthewsvolvosite.com/for...php?f=1&t=8830
In short switching from hot to cold air intake on a volvo is universally accepted as a quick and easy way to improve both fuel economy and power. It has been tested many times over.

Air filters tested: Testing a 'performance' air filter for MPG - Part 2 - MetroMPG.com

It depends on the car. Some cars will get more power, some will get less.

My old Hyundai got better FE with a cold air intake and a bunch of lightweight goodies hanging off the engine. My economy dropped when I put back in the stock airbox since it did not flow very well.

Now my current car gets better FE with warmer air entering the stock airbox. I haven't tested a cone filter WAI on the car yet. The frame opening the airbox feeds through is being blocked this winter to make a "poor man's WAI".

IDK, I think 90% of the time CAI gets worse gas mileage.

In the Corolla community, it seems that the '03-'04 models with a cable throttle body usually do get better f/e with a CAI, but the '05-'08 models like mine with an electronic throttle body usually seem to get worse.

Volvo used very aggressive spark advance coupled with knock sensors (usually 2) and high compression on all of its NA engines. As soon as you feed the engine hot air it retards timing and you lose both power and FE. A 1992 the white block engine with a stock 10.7:1 CR is perfectly content running on 87 octane (volvo recommends 91) so long as you feed it cold outside air. As soon as the thermostatic intake heater fails in the HOT position drawing air from near the exhaust manifold (usually does after 10 years) both FE and power take a dive. Most owners and mechanics are unaware of this little component. In California this little part causes a lot of volvos to fail Smog Check because of high NoX. CAI is king.

Here is the stock thermostatatically controled intake from a Volvo. The intake is designed to maintain a MINIMUM 70f for the incoming air. When the intake temp is above 70f, the airflap moves to the CAI only side breathing cool air from in front of the radiator. When the temp is below 70f it mixes in more air from the HAI side which is hooked up to a tube off the exhaust manifold heat shield. The colder the air, the more hot air it breaths. When the thermostat fails (its a cheap $5 part) the flap ALWAYS sits in the hot air side (as pictured) no matter what the intake temperature. The intake temp can reach close to 200f which can eventually damage the mass air flow sensor.
http://img.photobucket.com/albums/v2...g?t=1254273881

some good info, thanks