There are lots of driveshaft shops that will check and dynamically balance
your driveshaft.
I've had several made from bits and pieces. When the pros finish with them
they are pretty, straight, and perfectly balanced. Don't even mess with
measurements, it's cheap to get it done.
By the way, unless you have true overdrive, I doubt your driveshaft is
getting to 13K.
In my humble experience, high end miss is usually caused by the familiar
old bugaboos--fuel or spark, most likely spark. Even if it doesn't happen
in the lower gears. High gear, high RPM is the highest load your engine
sees, which means highest combustion chamber pressure and highest voltage
required for the spark. It's also frequently caused by too lean a
mixture--same root cause. I'd try closing the plug gap to .010" and see if
that has any effect. If it does, it's your sparks--and it doesn't matter
what kind of system you have, you can have something truly bodacious and a
weak coil at high RPM will let you down.
The second thing to try is going up big on the main jet. I don't know
whether you have SUs or Webers. If it's webers, go up four or five steps,
and see what happens. It won't be optimal, but it'll tell you what's going
on.
-----Original Message-----
From: BillDentin@aol.com [mailto:BillDentin@aol.com]
Sent: Monday, February 04, 2002 3:15 PM
To: Kaskas@earthlink.net
Cc: fot@autox.team.net
Subject: tolerable DRIVE SHAFT run out?
Hi Kas:
Hope you are well!
We are still working on 'high end break up', and John Reimer, a very
successful local ROAD/ROUNDY ROUND/DRAG racer friend (from the old days)
something to the effect of, "If you don't have similar symptoms in other
gears (at top RPMs)", he would be looking at something spinning that is
out
of round, and at top speed perhaps we have past the tolerable limits. He
said he would look first at the drive shaft. the Thunder Bolt has a one
off
drive shaft. Using less than laboratory equipment in our own shop, we
suspect we have 20,000ths out of round at one end. Is that too much when
we
get to 13,000 rpms (read 6,500 actual)? Any idea what tolerable limits
might be?
Appreciate any thoughts.
Bill Dentinger
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