> With a .100" shaved head, about what ball park would the compression ratio
> be? I may do the measurements and math, but does someone have a general
> idea?
Depends a good deal on what else was done to the head. The "comp prep" manual
says to remove metal from the combustion chamber, which lowers the CR again.
> With that much off, how do people deal with insuffient valve lash? If you
> put in shorter push rods, doesn't that still leave bad geomitry that will
> side load the valves work on the heal of the rocker?
Nope, the geometry between the rocker and the valve is set entirely by the
rocker pivot location, ie the rocker shaft. Shaving the head only screws up
rocker geometry on engines that move the pivot point to set the lash.
> Do people go to roller rockers?
Some do, but rarely is the improvement measurable. And roller rockers don't
solve problems of insufficient lash, or geometry. Plus, they bring problems of
their own, especially if the new shaft isn't hard (strong) enough.
> Where would you get them?,
I believe even Moss sells roller rockers. Other sources include all the usual
TR "performance" parts suppliers, like BFE, TSi, Racetorations, Revington TR,
etc.
> or the shortened push rods?
I got mine at BFE. In addition to being available "off the shelf" in .100"
short (custom lengths take longer), they are far stronger than the stock
pushrods.
> I see the steal compression lowering gasket in Moss
I can't seem to find it on their website, but I think you'll find that the
gasket itself does not lower compression. Instead, it's the "shim steel" gasket
that was included with the factory compression lowering plate. The gasket
itself is even thinner than the stock head gasket, so using just the shim steel
gasket will raise, not lower, compression. It's primarily useful in that,
unlike the stock head gasket, it can be trimmed to fit with modified or oversize
liners.
> Not sure how thick that gasket is either,
> anyone know?
If it's the "shim steel" gasket, then installed height is about .010". I don't
recall how tall the plate was, but since AFAIK it's been NLA for a long time, it
really doesn't matter. If you really want to continue in this direction, Mordy
Dunst can cut you a solid copper head gasket in whatever thickness you need.
http://www.headgasket.com/
However, keep in mind that shaving the head only reduces combustion chamber
volume over the smaller area of the head opening, roughly 1/2 the bore; while a
taller head gasket increases volume over the entire bore. Thus it would take
only (very roughly) .050" more gasket to compensate for .100" of head shaving
... which still leaves you with short pushrods. Also, moving the "squish"
surface of the head away from the piston decreases turbulence, which may affect
performance.
> Any other thoughts on the sitution of using this shaved head vs. rebuilding
> my stock one?
I would probably still go with your original idea. Shim the pedestals, then
have your original head rebuilt and plan on reinstalling it after driving season
is over. Or, if you find you like the extra performance of the higher
compression (and don't mind paying for premium gasoline, plus possibly an octane
booster depending on what other head work was done), you could go ahead and get
a set of shortened pushrods and take the shims out.
Randall
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