Drag racing part 2, slipping clutch?

[Michael Gough]

Hey everyone!
Last night I had another wonderful time at the drag strip, though it was
frustrating. Car is my 1988 VW Quantum syncro turbo BTW.
2 weeks ago, I went, and ran a best of 16.8 @ 79.5mph in the quarter mile.
Last week, I fabricated a cutout, with a removable plate on it, and welded
it into the downpipe. Now, even though the downpipe is still ridiculously
small (under 2") it seems to have a bit more power, and sure makes a cool
noise, especially when the turbo is spooled :)
Anyway, with the cutout un-capped, I made my way over to make my first pass
of the night. Rev'd it up, dumped the clutch, got a bit of wheel-spin on the
slippery track (I'll have to fix the diff-locks) and the car ran like crazy
to a 16.0 @ 82.7mph (at 2660 feet). I thought woah, that cutout does more
than make noise! Anyway, to make a long story short, EVERY run I made, was
consistently worse! I can't think of what would cause this, other than a bad
clutch, or the motor slowly dying, though this seems unlikely. Here are my
times....
16.0 @ 82.7
16.1 @ 82.1
16.2 @ 81.7
16.5 @ 78.5
16.7 @ 78.7
16.8 @ 80.1
More info, at this track, they give you 5 incremental times, for points on
the track. My times are all slower as the night went on, at every increment.
It's not loosing power only at the top end, or bottom, it's loosing power,
or slipping it away, throughout the entire 1/4 mile.
After the last run, I knew something had to be wrong, so I figured it was
better to pack it up and go home, rather than break something and have to
walk home. I didn't notice the clutch slipping, but I was too busy
concentrating on keeping the car on the track, and shifting ever few seconds
with the close ratio 'box to notice it. If anyone has any clues what else it
might be, please let me know.
Thanks
Mike