[Jay S]

If you plan to use 93 octane then the 72 cc heads are fine. But, it really isn’t worth the power gains in my opinion to go from the 84 cc to 72 cc. It really isn’t enough cam or head flow to see much for power gains with that extra compression.

The 87 cc E head d port with your combo would run on 87 octane and make around 450-460 HP with the RA manifolds. The 72 cc would probably be about another 10 or 15 HP and jump up close to 5 points on octane. If you want to run 93 and want the extra 10HP there is nothing wrong with the 72 cc heads.

There is someone on this forum with a 455HO combo that has 87cc E head round ports (factory 455 HO TA with RA manifolds) on the same short basic short block and cam as you have, that takes a minimum of 93 octane. On 91 he has to pull timing out because it pings. That car would not be close to running on 93 with 72 cc heads. The thinking that Aluminum heads can automatically run 11:1 compression not matter how the engine is set up is not true. Especially on something less than 93 octane.

I can’t buy 93 octane in many places, 91 is all I have available. Some places here in Nebraska 87 is all that is available. How long till that happens in your area?

Your engine as it is now should run on 87 octane. Running on 93 is actually making less HP than the lower octane fuel. Extra octane above what you need hurts performance some.