Is there a way to determine if the static compression ratio is high enough to make power with a particular cam profile without having the necessary piston, deck, gasket and chamber volume info to do the calculation ?

Would the compression pressure psi from a simple compression test be a reasonable indicator of sufficient or insufficient static compression ?

My cam specs are 262/272 intake/exhaust duration at 0.50 with 0.670 valve lift (solid roller).

The engine is supposed to have 10.6 static compression but that is yet to be confirmed.

Any idea what kind of psi a compression test would yield with this cam ?

How serious a power loss (percent) is there for each point of compression going down from 12.5 to say 9.5 ?

Search out Pat Kelly's dcr calculator. It will calculate your static compression ratio, then figure dynamic from intake closing point. You'll need your cam timing events and good data on everything else. Figure less that 8:1 is too low, 8-8.5:1 is pump gas friendly, higher is race gas territory.

Thanks, found the site, tried out the calculator with some guestimates on gasket thickness (0.039) and deck height (0.020). The rest is known and I came up with a DCR of 8.6 for the Beaumont. Will get the actual gasket and deck height next week. But it seems to be in the ball park for this engine.

The other engine I am working on varies from 7.7 to 8.5 depending on piston domes. If the pistons are the small 0.095 inch dome then a piston change is likely in order.

Still would be interesting to know what kind of cranking compression pressure there should be in a fairly stout engine and how the hp falls off with lower compression ratio.

Here are a couple of examples using a 30 over 454:

Cam intake duration of 315 degrees (advertised) along with appropriate head, piston, deck and gasket numbers to come up with a static of 13:1. With this much intake duration the dynamic compression would be only 8.2

Cam intake duration of 280 degrees (advertised) along with appropriate head, piston, deck and gasket numbers to come up with a static of 13:1. Dynamic compression would be 9.9.

Which 13:1 motor is gonna make more power, the one with the 315 duration cam and 8.2 dynamic compression or the 280 cam with 9.9 dynamic compression. Assuming both cams had the same lift.

Sandy, personal opinion - have used the DCR and do find it a little helpful. That said, you have to ask yourself - will the intake valve flow enough to empty the cylinder/combustion chamber in the time it takes for the valve to go from .050 to seat - the answer is no. I have seen DCR based on both seat (advertised) and .050. I think you are far better off calculating the effects of duration at another published figure. Take a look at any cylinder head flow chart, the .050 lift flow is somewhere around 30CFM - if the valve is held at .050. Depending on the cam and RPM, the actual pumping loss may only be 1CFM (or less). I think it is a great tool to understand the dynamics of a valvetrain, but in no way is it the final word. Key is, use the quickest seat timing to get valve train stability for the .050 duration and lift that you want. From what I can gather - lift intensity of 49* to 59* seems to be the normal range with solid roller having less. depending on where you actually take the measurement.

Generally around 4 percent loss in hp for every point drop.

So going from 12 down to 8 CR,, you are looking at somewhere around 16 percent so on a 400hp motor about 64 hp down ROUGHLY!!!

I say roughly b/c this stuff varies....

pdq67