<VV> Maximum cruising RPM

[Brent Covey]

> Just wondering what the maximum cruising RPM consistant with engine
> longitivity is, anyone have an idea ?

I know I read somewhere (likely something Bob Helt discovered) that the
3839891 cam started losing conntrol of the valvetrain somewhere around 3700
rpm, basically the lobe dropped out from under the lifter and left the
valvetrain sort of unsupported around that speed, and more problems develop
as the rpm go up from there towards 5000+, from a valve pounding/bouncing on
the seats and wear and tear POV. 3872304 cam is supposed to reduce these
issues if I recall the artcile correctly. Corvairs have pretty heavy
valvetrain parts and weak springs. I imagine the valve lofting issues occur
somewhat lower rpm as the springs weaken. Small changes like fresh
valvesprings and ligher retainers may help raise the rpm where the onset of
issues occurs even on stock engines.

I think its important to remember the wear will just be sharply increased
over lets say 3500 ish but there is not much likelihood for dramatic wear
under 4200-4500 probably if you arent running heavy throttle, very HOT or
very lean. Under 3500 you can expect basically negligable wear- running
80-85 mph on the freeway you might need to put valves in at 100,000 miles,
instead of 'never'. Running 100 mph with 3.55 gears will pound the valves
(and likely much else) out in short order on a stock engine if done beyond
the occasional short burst. Damage is greatly increased by high temperatures
softening the materials of course, so continuous heavy throttle and high RPM
in tandem is a no-no.

GM seemed satisfied with the wear and tear stuff to 80 MPH it seems anyhow,
judging from thier internal prototype test stuff, like the 1966 AIR car
report. After that you're on your own, apparently. The 5200 rpm redline HP
peak on the 140 apparently is determined by the valves beginning multiple
seat bounces on the cyl head, which is a recipe for destruction, 140's have
stellite faced valves that are pretty tough and still pound out fast if you
run them very high rpm.

I have found the 3.27 axle sure makes the 110HP cars nicer above ~65 mph
from a noise point of view.

Hope thats some help,
Brent Covey
Vancouver