This is a post I put up on another site in the beginning of last summer:
Ok, I have been tuning with plugs and timing for 2 weeks now after I realized my .030 over 427 with .250 long rod, 110cc RaceRites, 10.4-1,custom piston, rpm airgap,248/260@50 custom grind BBC responded to more timing than 38 deg. I have settled on 48 deg timing and a 7373 NGK plug. The timimng mark on the plug strap appears to be right where its supposed to be and the fuel ring actually reads a little wide on the porcelain. Its light chocolate color too which is saying a tad rich but because im shell shocked at the amount of timing that its taking im hesitant to drop the jet. Its got a 750 Holley ultra aluminum on it with 74 in front with pv and 81 in rear no pv. Thoughts on this anyone? And no I have not errored on setting the pointer! BTW this is a pumpgas street car. Also the amount of drivability/performance gain from 38 to 50 is super cool!
3 MO ago I removed the engine to fix a rear main seal leak. One thing led to another and I dug into the engine to re-verify some things/change a couple things. I found TDC to be spot on like I knew it would be. Bearings looked good along with everything else. One thing I did find is that it was not 10.4-1 compression so I removed the felpro gasket and installed .027 cometic plus advanced cam 2 deg. It is now 10.3-1. Cam is 248/260@50 with 580/600 lift. Also installed 2" primary hustler headers with 3" exhaust. Fired engine up the other day and all is well. I figured that 38-40 deg timing would be the max with the new compression and cam advance. I was wrong. It stumbled in neutral so I put it up to 42 and it got better....finally back at 48 deg and this thing revs better but certainly acts like it wants even more! why does thing take so much timing to wake it up?? Also when the timing was at 38 and I drove it the valve train was real loud. the more timing I added, the better it ran and quieter! Already on first fire up at 40 deg timing the valvetrain was quieter. I'm attributing that to advancing the cam. I know that's bizarre but that is whats happening. At 48 the thing at idle sounds so damn good both under the hood and out the exhaust. I have not been able to drive it yet.