Re: Hemis

["Joseph Kanellopoulos" <kanellj@domain.elided>]

Fellow Alfisti,

just to throw my 2 cents into it, I am a little confused as to how exactly a
pushrod offers more geometry flexibility that an OHC design.

Honda, Yamaha and of course many others, have demonstrated you can pretty
much do ANYTHING you feel like (including "ovals", perfect hemis and others
VFR, XR, FZ) when you have OHCs.

I also thought that shapes of combustion chambers besides filling mostly
affect the combustion efficiency, and arent most pushrod engines forced into
a crossflow arrangement, which is not a really efficient one for filling or
emptying a cylinder? Besides the many questions addressed here I did not see
fuel consumption mentioned and I think OHC engines are usually better.

I thought OHVs are really great for simplicity of construction and
maintanance since self adjusting hydraulics are much easier to design into
them but I also thought that you get a slightly "thicker" block and quite a
few pieces on the valve train that do not have to be extremely tight in
manufacture.  My basic understanding is that it makes for a system that does
not need a lot of tight tolerance or maintenance.

Finally, though I am sure OHC might add in complexity, I am not sure that a
bigger displacement same physical sized engine is lighter since I do not
really think that the valvetrain is the heaviest part of the engine.

My biggest pro for a pushrod would be engine/hood clearance, where it
becomes extremely efficient.

I think the ultimate example is offered by GM itself. A few years ago a
Vette owner gave me a Corvette magazine that is publised by GM for Vette
owners that had the new then current Vette pitted against the ZR-1.  Mind
you that the new Vette, has probably a much better suspension and a better
weight distribution, thanks to a rear mounted transaxle alfa like, that the
ZR-1 does not have.

At the end in the track the ZR-1 escaped as the winner merely by the virtue
of the very well Lotus designed ZR-1 engine that was of course though much
more expensive to built (at least for GM) than the new engine is.  (I
believe actually the ZR-1 engine was built by Mercury Marine though I am not
sure on that).

So a jewel of an engine, can turn things on their head, and that is the
point of my story,

Thanks,

Joseph
OHC Milano Verde ;-)
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