On Feb 10, 2005, at 18:58, Francesco Fontanot wrote:
do any of you know if you can stuff bigger valves to the 16v? What´s
the
stock size and what, if possible, is the biggest?
There's not much room in the 16V combustion chamber for larger valves.
It doesn't
matter much, especially on a streetable motor, since going much larger
on the valve
head diameter will lower charge velocity, which kills the already
somewhat weak bottom end
torque of 16V motors. Techtonics Tuning sells 28mm exhaust, 32mm
intake valves that have the
standard 7mm stem undercut by 1mm, which improves flow without having
much effect on charge
velocity. These are neat, because you don't have to do a bunch of work
to enlarge the valve seats.
They also sell 32.5mm oversize intake valves with the 7mm undercut
stem, and 28.5mm oversize
exhaust valves with undercut stems, made from Inconel (Inconel is a
stainless steel alloy that can
withstand extreme temperatures). The exhausts are Inconel, since the
factory exhaust valves are
sodium filled. I don't yet know if the .5mm oversize will kill too
much bottom end, but I'm going to find out.
It's almost time to freshen up the head on my '92 GTI 16V, and I plan
on going with either the standard
diameter valves with the undercut stems, or the oversize/undercut
valves. My decision will be based on
what Collin Geynes, TT's head guru, has to say about their specific
effect of each on bottom end/mid range.
--Holland
[email protected]
