Non-SE-R: GM OHV engines

[Jack Ray]

the Jez wrote::
>>One thing OHV engines got over OHC engines is torque off the line, they
>>aint got shit for top end.

Bill wrote:
>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?

Since OHV engines have all that valve train mass, they start hurting
mechanically when
forced to high speeds.  There's a lot more valve train stress on an OHV engine
at 7K rpm than
there is on an OHC engine of the same size at the same rpm.

One way to make up for a lack of 'revability' in an engine is to just make it
big and don't worry
about power at high rpms, just make it big and tune it (camshaft, valves,
intake and exhaust
design, etc.) to be efficient at lower rpms.  For example, GM's ancient 3.8
liter V6 has low power
per liter, so some would say it sucks.  But, for what it is used for, it's an
EXCELLENT engine.
It moves heavy Buicks, Pontiacs, etc. at a rather spritely rate (considering
the mass of the
car) without having to rev it up, and it gets around 30 mpg on the interstate
(IIRC, and I think I do).

So, Bill, you're right, it makes absolutely no difference what opens the
valves.  But a big OHV
engine will make much more power (torque, horsepower, it's all the same) at
low rpms than a
small OHC engine at the same low rpms and, conversely, that big OHV engine
starts running out
of steam at high rpms, where the small OHC engine shines.

I keep re-reading this and thinking "crap, you could do better than that", but
I've spent too much time
trying to write it clearly already...

Jack (I've said enough) Ray
94 SE-R