[Ragtop Man]

Be sure to cc the heads you plan to use before you get out your wallet.

Pontiac published CR's that were higher than delivered, sometimes substantially to give sportsman NHRA teams a little more leeway at tech inspection. The chambers are typically a skosh bigger than listed.

The longer the exhaust valve cycle and the later the exhaust valve closing point, the more static cr an engine can tolerate on the same gas. But, that pushes the torque curve up higher in the rpm range, and can negate the best qualities of a Pontiac V-8.

A dished piston is definitely the best way to go, there are some different ways to achieve it, but deepening the relief under the valves is the best way to go; keep the deck clearance as tight as you can without banging the piston into the head.

Rule of thumb with a traditional Pontiac and bathtub chamber is to just move the decimal point on the static cr to find your ideal R+M/2 octane with typical ignition advance... 8.7 = 87 Octane, 10.0 = 100 octane, etc. As noted below, the lower heat retention of an aluminum head will raise the octane tolerance, too, by how much is open for discussion depending on cam timing.

Don't worry if you are a touch light on the static CR; it will let you put a little more spark lead into the engine. Also, be sure your carb tune is right on the money; if it is running too lean, or not calibrated for the transitions, it will rattle like a poltergeist.

[Ron Landis]

Originally Posted by Ragtop Man

Be sure to cc the heads you plan to use before you get out your wallet.

Pontiac published CR's that were higher than delivered, sometimes substantially to give sportsman NHRA teams a little more leeway at tech inspection. The chambers are typically a skosh bigger than listed.

The longer the exhaust valve cycle and the later the exhaust valve closing point, the more static cr an engine can tolerate on the same gas. But, that pushes the torque curve up higher in the rpm range, and can negate the best qualities of a Pontiac V-8.

A dished piston is definitely the best way to go, there are some different ways to achieve it, but deepening the relief under the valves is the best way to go; keep the deck clearance as tight as you can without banging the piston into the head.

Rule of thumb with a traditional Pontiac and bathtub chamber is to just move the decimal point on the static cr to find your ideal R+M/2 octane with typical ignition advance... 8.7 = 87 Octane, 10.0 = 100 octane, etc. As noted below, the lower heat retention of an aluminum head will raise the octane tolerance, too, by how much is open for discussion depending on cam timing.

Don't worry if you are a touch light on the static CR; it will let you put a little more spark lead into the engine. Also, be sure your carb tune is right on the money; if it is running too lean, or not calibrated for the transitions, it will rattle like a poltergeist.

and to clarify...the zero deck helps flame propagation which in turn makes for a more complete burn and reduces detonation. As far as aluminum heads...as a rule of thumb they afford you about one full point in compression as far as pump gas goes.