[STEELCITYFIREBIRD]

My thought was without a quench pad on the piston, the engine would be more octane sensitive.
I'm always curious on higher compression 400 builds, always looking to learn.

[Formulajones]

It would depend on how the 614 combustion chamber is.

In some cases it just doesn't matter.

Here's one I did with #13 heads in a 428. Needed a 16cc dish in this one. Look closely at the flat (quench area) of the #13 heads. You can see the circumference left by the head gasket.

Now look at the piston and the circumference around the outside that gives you quench.

As you can see, there is no more quench to be had with this setup. A "D" shaped piston wouldn't have done squat for quench here. There just isn't that much flat area on the cylinder head left unused that makes enough difference.

Now if we were using a more modern heart shaped combustion chamber, then things would be different. But even with that said, GM has been building LS engines for years with bowl shaped dish pistons and modern combustion chambers and look how well those engines run

[bignate]

OK just to update this thread... I finally had some time and a nice day to play with this thing. I put a fresh set of plugs in it gapped at .040". Then I checked the timing curve with my new timing light. (Wish I would have bought a nice one a long time ago!) Initial advance was 16°. Total was coming in at 40° all in about 2000rpm. So I pulled the distributor and checked what was in it. I had one light silver spring and one blue spring in it. I had the blue 21° bushing in it and it had a flat spot worn on it.

I put the two blue springs on it and a new 14° bushing I bought. I then put it back together and set initial to 18°. Now total is 32° all in about 2900rpm verified by my timing light. It also did gain about 1/2" of vacuum at idle.

No dyno time or track testing but my butt meter is impressed! She's a handfull now! much more responsive under 3000rpm. I feel I have a good baseline to go from now. Can't wait to do the conversion to EFI!

Nate