My first entry to this forum. Hope someone is able to help-

I am in the process of rebuilding a '69 RA III 400 from a '69 GTO convertible using the 4-bolt block and #48 72 cc heads. Seriously need to get the compression down to at least 9 to 1. Also believe i should zero deck the block because have heard this adds to the detonation problem... that would even possibly raise the compression, correct? Are there any dished pistons generally available to deal with this situation? Possibly any relatively high output cams that are designed to lower the effective compression pressures?

Thanks for any input!

Judd

You have to change the pistons. 90% of compression is the pistons, any significant change will have to be made there.