I have a .060 over 396 with 049 heads and a small dome (maybe 1/4"ish) on the pistons, I'm guestimating about 10.5:1 Compression ratio. Edelbrock performer 2.0 manifold, with a 750 Edelbrock carb on a 2' open spacer. Unknown (has a mildly lopey idle) solid flat tappit cam, stock looking fuel pump, and stock style HEI distributor w/ vacuum advance hooked to the non-ported nipple on the carb. It's in an 18' flat (well, almost flat) bottom, I think the gears are 18% OD. When I'm not heavy on the gas, engine temp stays right around 120, and if I hot foot it, it'll climb up to about 160 or so.
I have 3 issues at the moment.
- On the top end it feels like she's running out of fuel, back off the throttle a bit and she comes back to life. I'm thinking it could be a fuel issue. After reading some other posts, I also thought the sparkplug gap might be a bit wide (0.040).
- I haven't put a timing light on her yet, but there seems to be a very fine line between detonation and backfiring out the exhaust. Advance it a cnut hair and it detonates under load, like 3/4 throttle acceleratin out of a turn. Retard it a smidge and at full throttle it pops and bangs out the exhaust, only at full throttle on the top end. I have found a happy medium, but starting is a pain in the butt. Turns over nicely with the ignition off, but struggles to turn over with it on.
- RPM... I was hoping to be in the 5500 to 6000 range. The original testing prop was a 12x16 3 blade OJ, and the most I could get out of it was 4200. So, I put on a 12x14 3 blade OJ and the RPM sounds a bit higher but the tach is still saying 4200ish. The boat feels quicker, but slower on the top??? I'm thinking the issues listed above are the limiting factors to RPM. Any input?
So, my questions are:
- What should I gap the plugs at?
- Should I put lighter mechanical advance springs in the distributor?
- Is the Compression Ratio possibly too high for premium pump gas?
- Am I asking the right questions?