318 Compression ratio

rick360 said
I've read into the ThermoQuad and there are two types with either smaller primaries or larger ones. 800cfm for the smaller ones supposedly. They used them for the small blocks the other ones for the big blocks. The secondaries are the same size in either one. I'd need a pretty high duration cam to use one then?

It's easy to over carb a street 318. As someone else has stated, the beauty of an air valve secondary is that it opens when the engine can use the additional air flow. The Carter AVS, Edelbrock Thunder AVS, Carter Thermoquad, and Rochester Quadrajet are all air valve secondary 4 bbl carbs. The AFB has a mechanical secondary. I'm not familiar enough with the Holley line to advise which are mechanical and which are air valve secondary.

rick360 said
Also using the smaller 1.78 valves would keep good flow velocity correct?

Unless the 302s were going to be subjected to extensive work, I stuck with stock valves. I did consider going to the 360 (1.88/1.60) valves, but I never followed up on it. I had a budget number on the engine. I was a little over.

rick360 said
Are those pistons you mention the Federal-Mogul 1.745 compression height?

The 67-69 have a compression height of 1.759, 70-71 is 1.750, 71-86 is 1.739. These are stock pistons. The 67-69 have four valve reliefs in each piston (see photo of my 68 in the Demon). This piston sits .0036 below an un-cut stock block

rick360 said
You use a thin head gasket?

Yes. No problem with piston to valve clearance.