I like the vortec heads but am still concerned with the compression ratio a 64 CC head will produce on these Iron Heads. I'll be installing on:

Chevy 350 bored to 4.030
flat top pistons w/ valve reliefs

I calculate the compression ratio to be right at 10 to 1 with a standard head gasket. I just don't want to worry about spark knock. Am I being too cautious?

I run almost 10.5:1 with vortecs no problems. I know someone with close to 11.5:1 with vortecs and they run fine on pump gas (which nobody believes).

We run flattops in our 350 using Vortec heads. My brother calculated a static ratio of 10.5:1, and we've never had a problem with detonation. Of course, you should run 93 octane with these numbers.


Caveat: your results may vary

You have to check the dynamic compression based on your camshaft, to know whether or not 10:1 is going to be too high.

I can tell you that with a 10:1 static, Comp XE 262 cam, I didn't see detonation with 92octane, but sometimes got some with 89octane.

The vortec chambers are supposed to not allow as much detonation as a standard older head.

I have real problems with the junk 91oct. in Cal even with dished pistons. My cam is awfully mild an XE-256. With more cam and some better gas you might be alright.

Like Twilight said, it depends on the dynamic CR.
My CR is about 10.9 with a 276 solid cam. My car took a little tuning to not ping. And a cold air intake and a 160 stat. It starts pinging at 175*f. Haven't had time to mess with it to find the fix.
So, yes YMMV.

385 stroker, 214@.050 single pattern cam, 10.2:1 static compression, stock HEI [way too much vaccum advance for vortec's combustion chambers] and 91octane all day long with AZ 110* heat.