Lunati Voo Doo Cam.

nm9stheham said
Some chamber polishing might help. I'll venture to guess that no quench and the slower overall burn rate in the open chamber are probably what is limiting the CR for you. (I also wonder if a manual trans set-up will be less forgiving.)

I was gonna ask about ignition timing but you have addressed that. Have you slowed the rate of adding in the mechanical advance? (I.e., heavier springs...)

Chambers were cleaned up some when the larger 2.02/1.60 valves were added and the porting was done. They're not polished, but they aren't exactly stock either. I run KB243's that are .018" over the deck, which is why I run the open chambers, so the quench is not ideal. The manual transmission doesn't help, and the 3.55 rear gears add to that. If I had 3.91's it would probably be less of an issue. Timing is set up at 20* initial, it's at 34* all in mechanical with no vacuum advance. I pulled it back from 36* all in. I use a Mallory Unilite distributor, I forget the exact spring combination because I ordered a few different spring kits to play with, but I set it up to start advancing about as late as I could. All in mechanical is about 2,800. Cranking pressures on my 340 are 175-180 psi.

I've messed around with the tune quite a bit. Again, I'm not saying it's perfect or anything. It doesn't detonate the way it's set up now, but, there isn't a whole lot of "wiggle room". I'm pretty sure I couldn't step down on the cam without dropping the compression a little, say 9.5:1. But that's just what I've encountered with my engine, I'm sure it's possible to get away with more. I just don't think I can with my engine.