[Green Hornet]

I'm familiar with Pontiac V-8's...from 67-78....but just learning about early 389's

According to Pete's book...ALL 59's used the same head casting.....so how did we achieve 3 different compression ratio's of 7.8,...8.6 and 10.00?

I see that different cams were used...but don't think they would change that much in CR...

Were there reliefs ground in cylinders. to reduce CR..like the 409 truck motors?

I need to check my block cast number......Hopefully that will tell me what I have..

[b-man]

Lower compression ratios were achieved with dished pistons, export engines had reduced compression as well. No difference in block machining.

The 10.5:1 Tri-Power engines had the heads milled .030” if I’m not mistaken.

Dished pistons: https://www.ebay.com/p/1070477518?ii...BoCcxYQAvD_BwE

The vast majority of 1959 389 engines were the A-code 280 hp 2-barrel version which is likely the one you have.

Link to thread with more ‘59 389 pictures and information: https://forums.maxperformanceinc.com...d.php?t=781327

[CATBIRD]

He has a Bonneville. Same exact engine as the 280hp with a 4bbl carb making it 300hp. Same compression, same valve train, just more air into it. I was under the impression that the combustion chambers for the 10.5 engines was cut a little shallower, but I could be wrong. Pontiac did machine their combustion chambers......John