Originally Posted by harvey

I had read on here that removing the snorkel ie. the inner wing resonator box was a performance mod. I had done it a couple of times in the past but could not determine any gain. (Unless you wanted more noise from the induction) On this occasion with an STi 3 Wagon I wanted to test various panel air filters and see what gains were to be had from the snorkel removal.
The tests were conducted on a Dyno Dynamics rolling road at TEG Sport on 2 consecutive afternoons. The best power run was 335.5 bhp with the snorkel. The best power run after removing the snorkel was 325 bhp. After refitting the snorkel I immediately got 335 bhp. For me this was conclusive and I think that with the snorkel removed the air flow was sufficiently disrupted to cause the power loss.
I had cut 2" off the original snorkel so that it butted in to the inner wing to facilitate best possible air flow. I had to obtain a replacement snorkel to go back to the original OE system.
As the car was on a standard ECU (with standard injectors and turbo) it was not possible to experiment with fuelling to determine if there would be any gains with a mappable ECU.
The result was contrary to what I had expected but worthwhile as far as I am concerned.

Originally Posted by harvey

As reference has been made to some testing I did previously, please let me clarify.
Four pannel filters were tried.
The "best" performer in terms of power on two separate days was the HKS Green pannel.
Next O/E Subaru disposable.
Next was the K+N followed by the STi (disposable)

The difference was only 2bhp.
Prodrive (Mike Wood) confirmed my results were roughly in line with their findings.
The tests were done on a car with O/E ECU without any form of remapping which would not have been possible anyway and the chances of mapping making any difference for 2 bhp different air flow are extremely remote.
At the same time I also found that removing the inner wing resonator on its own resulted in a decrease in power by, (from memory) 5 bhp.


Tests were done one afternoon within 45 mins and as results were not as expected, repeated the following day with similar results.
Subsequently I investigated the filtering abilities of each filter as best as I could.
Clearly the HKS Green Pannel could pass quite large grains of sand.
There was no appreciable difference between the other three although I think the STi is probably best at filtering down to a small micron particle size.

On a car I am keeping, I would settle on a K+N as it is reusable and if the sales blurb is to be believed it has good service life. Otherwise I would use the O/E Subaru filter.

When the engine was rebuilt on the test car, I know the turbo compressor wheel was unmarked. That turbo was removed over last week-end and the edges of the compressor blades are finely peened and nicked. I will try and post a photo. I had not changed the HKS Green pannel but obviously now wish that I had done. Another lesson learned.
The car now has a replacement turbo and a K+N pannel on order from RCMS with a mapping session on the rollers with Steve Simpson this Friday.

At a later stage I will try a bigger turbo but while below 350 bhp I will stick with the pannel and O/E induction air box (without a MAF Sensor on the Simtek ECU) I may try an experiment, pannel/cone, especially above 350 bhp.

Originally Posted by corradoboy

Some people have ducted directly from the front of the car, usually through the foglight aperture, but there have been cases of MAF failure and dead engines when induced water, dirt, oil and whatever else overwhelms the filter and makes it into the induction pipe.

Originally Posted by corradoboy

FWIW, I have said it time and time before, the biggest performance upgrades come from a combination of improved handling, driver technique and a reasonable balance of power to exploit these. Too much power upsets this balance, as does crap handling or a rubbish driver. Big power numbers are for 'net and pub bragging IMHO.