[DeTomaso] Compression ratio estimate

[Jeff Cobb]

On Aug 11, 2013, at 10:02 PM, Boyd Casey <boyd411 at gmail.com> wrote:

> Dear fellow Panteraians,
> I have a question for the more technically savvy . Is it possible to come
> up with an estimate of your pistons compression ratio by measuring the
> cylinder compression?
Yes, a rough and meaningless dynamic estimate. The only true way is to cc the head 
while inverted and the BDC piston/cylinder then you will know the actual static mechanical ratio.
Or you could TDC the piston and measure fluid going in the s.plug hole, then lower that 
piston and pour in more measured fluid. Of course you will have to remove that cylinders 
rocker arms to kill the valves. Now you have the best rough estimate of your compression 
ratio because most likely you will have captive air around the valve area.
What is important is that all your cylinders create about the same psi after seven 
spins with wide open throttles, give or take 5% or so.
> As I have mentioned before I bought my car from the
> estate of a gear head who owned several auto parts stores and he spent
> allot of money on my Pantera when it was his. He was apparently a fan of
> Hall Pantera because allot of the Pantera goodies he bought appear to be
> Halls ( and there were lots of Hall literature and parts lists)
> The engine has roller rockers and Hall big bore headers and an in unidentified
> cam. Since I have not been inside the engine ( and don't want to until I
> need too) I am trying to find out as much as I can and if there are any
> forensic techniques for coming up with an educated guess
All answers will be a guess and knowing your compression ratio truly will only 
pleasure your senses.
Knowledge is power but only if you pull your engine apart will you find enlightenment.
As long as your timing and carb are set up for max power and no ping at max load 
then you will have all you can get. So many different cams
will give you so many diff ratios and most of the time the true static ratio means nothing.
What matters are how all systems work together to produce correct power.
> as to the engine
> components
You could spend many hours with a degree wheel so to plot your cam lobes and measuring 
the pushrods lifts to come up with some specs.
> I would appreciate hearing about them.
> Boyd
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Jeff Cobb