Mech Advance Only Distributor Timing

[olddog]

Tom Kirkham started a thread in the EFI and tuning section. He left several links a few posts later. There is a lot of reading, but the best info I have read to date. I still have a few questions though.

Bottom line is that your engine needs a bunch of advance at low load. That is partly to do with the lean fuel mixture. So no **** your engine runs better with a lot of advance. It may like as much as 52 deg at 2500 rpm and low load conditions. The problem is that at WOT the rich dense fuel charge burns much faster and the engine can only tollerate 35ish deg. Too much timing breaks engines, as you have already learned the hard way. Too little timing will make it run hot and slugish.

For mechanical only advance you must tune it only for WOT operation and let it run poorly at light load conditions. Big cams due to exhaust dilution from the overlap may need 16 to 18 initial, but do not go higher.

If you want it to run good at light load, get a vacuum advance on it.

I think the articals will answer all your questions and support what I have said. Good luck!

[scottj]

My motors always ran best without any advance so I've always lock out my distributors, but my cams have always had 260+ degrees at .050". On my 11:1 motors I didn't need the MSD start retard box as they always started without issue, but it was required (-20deg) on my high compression motors or they would blow teeth off the starter ring gear. A dyno is needed to determine optimal timing.

Scott

[69boss429]

Originally Posted by scottj

My motors always ran best without any advance so I've always lock out my distributors, but my cams have always had 260+ degrees at .050". On my 11:1 motors I didn't need the MSD start retard box as they always started without issue, but it was required (-20deg) on my high compression motors or they would blow teeth off the starter ring gear. A dyno is needed to determine optimal timing.

Scott

Question,
When you set the timing with your locked dist where do you set the mark?
With a digital timing light do you set total at TDC (say 32 deg or whatever your max is) mark or BTDC

[scottj]

Originally Posted by 69boss429

Question,
When you set the timing with your locked dist where do you set the mark?
With a digital timing light do you set total at TDC (say 32 deg or whatever your max is) mark or BTDC

I use ATI dampers that we mark with white paint at the actual deg BTDC as determined on the dyno. We only use the cheapo $20 timing lights, no dial-backs or digital. If for some reason we had to time the motor at the track, at night, it is a fool-proof method. While this procedure is for our circle track motors, I didn't have any good reason to do it differently for my Cobra motors. With locked advance and a good custom carb, my Cobra motors had better street manners than most others having 20 degrees less cam. In fact my girlfriend could easily drive it until I put a 3-disc button clutch and the Jerico in it.

Scott