How does this 360 Magnum combo sound?

vioperblue72 said
Insuring the life of your motor is worth alot more than $1.60 per tank. I still have my doubts you are at an actual compression ratio of 10.6 and not pinging with iron heads and a 268 cam. I run 10.7 with edelbrocks and a 286 solid roller, 32 total timing and have made it ping on 91 octane on a really hot day. If you are getting away with it that is great, but I wouldn't recommend having somebody else try it.

Well the engine is at 10.6:1 compression, I measured everything when I built it. The block was machined so the KB107 flat tops sit at zero deck. The heads were cc'd at 64 ccs. The bore on the head gasket was 4.150 and had an advertised compressed thickness of 0.039". I didn't measure the valve reliefs in the pistons and went with the 5cc advertised by Keith Black. I did not account for the gap between the piston and the top of the rings but with the KB pistons it less than a cc. With the Comp XE268 cam I get a cranking pressure of 180-190 psi in all my cylinders, that is high but within the limits for pump gas.

There are other folks on this forum with essentially the same build and compression levels that also have no issues running 89 octane so it's not a matter of getting away with it, its how you build the engine. The key is the excellent design of the magnum head and a very tight quench which makes the engine very detonation resistant. Drop the piston down in the hole for 9.x:1 compression and you will have more detonation issues than at the higher compression.

FWIW, the top three competitors in the Mopar Muscle sb engine shoot out used iron magnum heads and they all had compression levels in the 11's to low 12's and ran on 93 octane pump gas. That's certainly pushing it but mid 10's is not an issue.