Join Date: Jul 2004
Location: New Brunswick, Canada
I found this information very useful
We have tuned for I think almost every intake out there so I will offer a little feedback as well. Joel has it pretty much dead on in most cases, but not all intakes are created equal.
Most of the intakes on the market are just a cone filter on a tube in the fenderwell. The aftermarket tube is usually a slightly larger diameter where the MAF is located when compared to a stock one. This allows more air to pass by the MAF without being calculated for since the poor MAF still thinks it is in its smaller original house. This leans out the air/fuel mixture since the MAF does not know to tell the ECU that more air is being ingested. The factory WRX runs pretty rich so the leaning out of the mixture creates more power. The flow improvement is very small since the aftermarket intake is still somewhat close to the stock intake diameter in order to be able to still run on a stock ECU. The factory airbox is a pretty good design. The entrance to the tube has a nice air horn for smooth entry into the pipe and the air has a chance to get straight before hitting the MAF to ensure accurate readings. Since the box is not the major restriction, removing it with a tube is not going to make a significant improvement in flow. Your intake can only flow as good as the smallest bottleneck which in most cases on the WRX it seems to be the pipe diameter if a significant improvement is to be made.
Another thing we noticed with almost every aftermarket intake was that they caused almost random switches in the air/fuel mixture. At one part of the RPM band they would cause the car to run lean, a few hundred RPM later they would be richer. That tells us that that turbulence is likely being caused at the MAF. Causing it to read incorrectly and resulting in the changes in the air/fuel mixture. That is why most are a pain to tune for. The short “ram pod” intakes that place the filter close to the MAF are even worse. They cause so much turbulence at the MAF and result in changes in the air/fuel mixture that are so inconsistent that sometimes it makes a tuner want to give up on getting things correct. Compromising a good air/fuel mixture can make for less power than would have been achieved had the intake been left alone. Not to mention the inconsistencies in intake air temperature that also have an effect on the way you ECU controls things. Located on the MAF sensor is an Intake Air Temperature sensor that is susceptible to the same factors the MAF is.
One thing that can be a hard concept to grasp is that different is not always better. Just because a part is shaped differently than stock does not always mean it performs better. The majority of intakes on the market for the WRX prove this.
[ 14 January 2003, 09:30 AM: Message edited by: Josh ]