78Cutlass4Speed

I picked up an Olds 350 V8 two weeks ago for my 1979 Cutlass project I'm currently working on. It was in a 1974 Cutlass S and the owner wasn't sure if it was the original engine or not. The casting # on the front is 395558-2, the heads are #8, the valve covers have the "OLDSMOBILE" script on them, the intake has an EGR valve, and it's painted gold (under years of oily grime). I figured it was an early 1974 350, but the partial VIN on the pad is 39M134680 which decodes to a 1969 (short) block. It looks like I have a 1969 350 short block assembly with later heads and intake. I know in 1969 the 350's could have 9:1 or 10.25:1 compression and it was only 8.5:1 in 1974. Any guesses to an approximate CR? Still around 8.5:1? 9:1?
I don't know any other particulars about the motor except it's a strong runner that should give my '79 a nice bump in performance.
Thanks.

Fun71

Well, without knowing if the engine has ever been rebuilt and possibly has aftermarket pistons, there's no way to know for sure what the CR is.

I think the scenario for the highest CR is a factory block with original 10.25:1 compression pistons with 6cc dishes. The #8 heads dramatically reduce compression no matter what pistons are in there, though.

I put some numbers into a CR calculator and got the following:

Bore = 4.057
Stroke = 3.385
Combustion chamber volume = 80cc
Head Gasket thickness = .040
Head Gasket Bore = 4.20
Piston-to-Deck clearance = .025
Piston Dish = 6cc
Compression Ratio = 8.1:1

Now if it was originally a low compression engine with 14cc dish pistons CR = 7.6:1
If aftermarket 6cc cast pistons were used CR = 7.8:1
And if aftermarket 24cc rebuilder pistons were used CR = 6.8:1

AZ520

Just do a compression test, anything around 150 is a 8:5 to1 or less in pretty good shape, 160 and higher will be reaching 9 to 1, this all depends on the condition of the engine and your elevation or course. If your reading are 110 or less its pretty tired, but yours runs strong so it should be ok.