Hi, here's pictures (the best I could do) of top of piston.

Looks like High compression piston if I compare to Joe's ref picture, the notch looks conical not round.
Is the number 30 in the middle of pistion for 0.030" overbore ?

Thanks

 

Tancuda yours are low compression pistons.

The visual difference can be both subtle and obvious depending on angle.

Here is high compression.


And below is low compression.


Both are of 1970 Olds 350 engines.


Side note, I have seen inside my high compression engine with a borescope. It's a shallow dish like Joe Ps posted pic and the first pic I just posted.

 

Thanks for the reply, the recess in the middle on my piston looks deeper (and bigger too) than your high comp piston picture, more like your low comp, so surely low comp piston here.
I think my compression numbers reflect the low compression engine and looks good finally.

 

Did not know if I had to start a new thread but will continue on this one...correct me if I'm wrong

I will be doing soon a smoke test on the engine to verify again for vacuum leak, any tip or recommandation on the procedure ?

What port can I use to plug the machine onto the engine ? I heard booster line on intake !!

Thanks