[TThom]

Euro Cup cars and later turbos (250bhp) always had the same K26/8.
The "290bhp" was the official figure for 90' Cup cars though most produced slightly more than 300bhp.
I'm not discussing Canadian Cup cars as I have no experience with them.

I was pointing out that the airbox/snorkel has always been a proven and effective solution on Euro Cup cars, since they were tuned with it yet with a high amount of ignition advance in higher rpm for the ones for the 1990 trophy.

Since some seem to be dragging my point out of focus it's quite tempting to think that my physics grade in school were probably higher their grades in literacy and text understanding.
However, I'm willing to try again.
The airbox was obviously shaped to accomodate the rectangular flow section of the AFM, which has been a Bosch offering on VAG cars well before the 944 turbo came out.
It is also a documented fact that a stock K26 (6 or 8 regardless) doesn't create enough vacuum pre inlet to justify using a flow section larger than the AFM's.
It is also a documented fact that using the airbox/snorkel in place of a cone (regardless where it's located in the engine bay) will provide fresher air to a stock K26 turbo than a cone filter set up.
So basically : cone filter + AFM + stock turbo = some work and expense resulting in IAT increase.

Now let's replace the stock K26 for a turbo that flows a lot more. There we are limited by the AFM flow section which results in increasing the vacuum pre turbo inlet, thus affecting turbo performance (and possibly increasing oil suction out from the AOS line)
So, basically : turbo flowing more than stock K26 + AFM = some work and expense resulting in counter productive vacuum increase pre turbo inlet, regardless of cone or airbox since the rectangular flow section of the AFM remains the restrictive part in the pre turbo part of the intake line.