Can someone tell me if my compression ratio of 8.5:1 is good or not for a SL6

That's pretty good if it's a stock or other short duration cam. Most engines don't even have 8:1 stock. I tore one down that measure out to be 7.6:1.

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Joshua

If it actually measures out at 8.5:1 that's pretty good.

Exactly... the 60's engines I've torn down are in the high-7 to very low 8 range, and the 70's engines being a little better to stay above 8....

Are you measuring something somehow and thinking it is compression ratio? Like using a compression gauge?

It may be marked in both psi and 'atmospheres' of pressure. 8.5 atmospheres is around 120-125 psi which is pretty decent, if on all cylinders. Is this what you are really asking?

i was told that the compression ratio was 8.5ish:1 by its previous owner so i was asking to see if it was good

Not sure what the PO was trying to tell you. The compression ratio is only measured and calculated with the engine apart. I don't know of any common or convenient way to measure it in-car and it is not a field service measurement. It is a general specification of an engine, not something you measure to see if there is a problem or not.

Measurements made 'in the field' are cylinder compression (good is in the 120 +/- psi range stock for this engine, stock), and compression leak down, which measures the % of air leakage from a pressurized cylinder; that is measured in %.

So the number the PO gave you is meaningless as to the engine's condition.; it is just a book factory spec, or the PO built the engine to that 8.5:1 spec (and hopefully checked it in the build). Is this a stock engine?

For a completely stock Slant 8.5 would be very good. Without measuring everything it is just a number somebody pulled out of their posterior.

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Official Cookie and Mater Tormentor.

I believe mine is 6.8:1? Gotta look it up again. My block had insane amount of deck