Non-SE-R: GM OHV engines

[Tim Rogers]

Rick replied to Bill's question of:

> "Michael Jez" <93SER@attbi.com> wrote:

> >One thing OHV engines got over OHC engines is torque off the line, they
> >aint got shit for top end. Only thing that actually has balls for

> Why is this?  When the valves open, the valves are open, right?  Why does
it
> matter if it is a pushrod vs OHC actually doing the opening?

And basically told us why a pushrod motor will not live long at high RPM's.
He didn't mention why OHV motors tend to have more low end torque, which I
will try to rationalize here:
Generally, a mass produced OHV V-8 with HVLA's will only rev to 5000 or 6000
RPM, so there is no need to optimize the intake, exhaust and cams for
anything over that number.
Therefore, you end up with a motor that has long, narrow intake and exhaust
runners, and a cam set up to work with those constraints.  If you were to
optimize the motor to have better breathing at higher RPM, you would never
get to see the results as your motor would be eating valves over your 5000
RPM limit.
To put it in other words, the OHV engine can't go to high RPM's, so you may
as well optimize it for low RPM's.
The OHC motor can turn the revs, so you sacrifice a little bit of bottom end
to let it do some useful work at high RPM's and have a greater area under
the torque curve because your torque curve extends for another 1000 to 1500
RPM.

Tim Rogers
-93 NX T-top -needs wiring work
-91 NX - Racecar-to-be
-75 Silverado - Rusty Tow Beast