Edelbrock heads on a 340 with KB243 pistons

Edelbrock sells a modified head for the early 340's with the pistons that are .018" proud of the deck, they're machined for clearance with those pistons. They're basically an open chamber head. Not sure what their thinking is, but they actually make a head with a modified chamber. Maybe their reasoning is debatable, but they must have their reasons for doing that instead of just telling folks to run a fat head gasket, which would be a lot easier for them.

I have a set of KB243's in the '68 340 in my Duster, and they really are .018" out on my engine anyway. I ended up using a set of the later 308 heads (open chambers) and having them ported. Chambers ended up at 65cc's, compression is 9.8:1 and runs 91 octane ok. I pulled the timing back a couple degrees to 34* all in mechanical, no vacuum advance.

The problem with the closed chambers is that you have to run a thick head gasket for piston clearance so you end up dropping the compression anyway, and then you're running an aluminum head with less than 10:1 compression. Use the modified chamber eddy's and they're 65cc chambers, same compression. Obviously you can play with the clearance value a little. My expertise is not as an engine builder and I wanted an engine I could daily drive for a long time so I didn't want to get crazy with the clearance and the lunati 60404 I've got has .513"/.533" for lift so I ended up going open chamber iron heads and spending my money on porting. Which worked ok, the 308's flowed 264cfm at .500".

Like I said, I'm not some crazy experienced engine builder, I had my reasons for doing what I did and it's all a compromise. It's a heck of a lot easier to figure with zero deck pistons and closed chambers.