Rauchen,
"The trimming to get the hose end to mate up
to the back of the Kamei scoop is the trickiest- want contact but not so much force that it pushes the scoop out forwards."
I got mine hooked up tonight. It's sweet. I bought the 2-1/2" hose like you said. I ran it through the bumper and into the airbox as you directed. My Kamei scoops already had small holes drilled in them so I could secure them to my car with light steel cables. The bolts are very small and nearly invisible. I removed the bolt from my right scoop and used it to bolt the vacuum hose to the scoop. The hose fits perfectly INSIDE the opening. It's visible if you stoop down for a peek, but I intend to spray paint it to match the car/scoop.
Anyway, once the hose was bolted to the scoop, I was able to pull the hose from the inside until the scoop was actually being pulled into place... just the opposite of your concern above. Once the scoop was pulled into place, I trimmed the hose from the airbox side.
It turns out that the opening in the airbox is actually 3" instead of 2-1/2". My solution to seal up the gap was to wrap the hose with a bicycle inner tube until a good seal was formed. It's not perfectly airtight, but bound to be at least as good as the OEM setup. I may drive a screw into the hose (same as the ones that held the J in place) to ensure the hose doesn't jiggle out.
If you haven't tried to perfect your hose, give my solution a try.
Thanks Again For Your Help,
------------------
Scott, KE4WMF
98 Jetta TDI w/42,000 mi
53 mpg (US) w/AC
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[This message has been edited by RADHAZ TDI (edited August 27, 1999).]