Brent,
Welcome to the PY Forum!!!!
Your heads must be cc'd as there is a lot of variation in the combustion chamber volumes on stock Pontiac heads. I have seen many chambers that are advertised in charts as having a 72cc chamber, but in reality have more than 76 cc's of total volume.
On a 428 with a 72cc chamber, .021" deck clearance, a .041" gasket and assuming a 6.7cc piston dish, your 428 would have a whopping 10.62:1 static compression ratio (SCR) which is too high for most available pump fuels.
I am very conservative with compression ratios on street engines. Many feel you can safely run an iron headed Pontiac with 10.00:1 SCR on 92 octane pump gas and some do, but here in California where we have 104° summer temperatures, I prefer to stay under 9.50:1 SCR.
The common 6X-4 head, milled slightly to yield a 90cc chamber and zero-decking the block would yield 9.40:1 SCR.
What other machine work has been done to the block??? What rods are you using??? What type of transmission and rear axle ratios are you planning on using???...Robert
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