[DeTomaso] Compression ratio estimate

[cengles at cox.net]

Dear Boyd,


                  As a rookie engine builder, I agree with everything 
the Jeff said.   It seems tantalizingly easy to determine the CR with 
simple PSI measurements of a cylinder, but it is not accurate and short 
of, at least, a partial engine teardown you will generate only 
marginally useful data.


                                Warmest regards,  Chuck Engles


On Sun, Aug 11, 2013 at 10:37 PM, Jeff Cobb wrote:

> 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
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