Yeah, I'd call that run too. Definitely see what the ignition timing actually is idling in gear. If it is below 10*, that could be a problem. Normally, I would say hook up the vacuum advance to manifold vacuum so it boosts timing at idle. With a 500 HP motor, 20* of idle timing or locked out timing is optimal and will keep the engine cooler at idle and low speed.
Yepper, a MSD Billet Distributor (no vacuum advance). Though I could switch to a MSD Ready-To-Run Distributor (w/vacuum advance)...
You should be running the largest advance stop bushing (black), that limits mechanical advance to 18*. https://www.jegs.com/InstallationInstructions/100/121/121-8464.pdf That allows you to run 14-16* initial timing. Having a vacuum advance, you could hook it to manifold vacuum to give you even more advance at idle. The engine will run cooler at idle and low speed stop and go. Put a timing light on the engine and see what the advance is at idle in gear.
I know that, I am talking about mechanical advance. Read my post again. Do you know what an advance stop bushing is? A street car should use vacuum advance though. You can’t. If you did, you could use it to boost your advance at idle.
Yes, I understand about the bushings and springs and how they play their respective parts in mechanically advancing the timing as RPM rises. I got confused when you mentioned vacuum advance, since I didn't have it. So having, say, an 18 degree of max mechanical advance (as you suggest) with an initial advance of 14-16 degrees. I would have a total advance of 32-34 degrees. Wouldn't that be about the max of total advance?
Yes, but using the biggest bushing allows the least amount of mechanical advance (18*), and that allows you to run more initial for the same total. More initial advance should make it run cooler. If you had VA, you could have even more advance at idle. I am just saying to run as much initial as you can. Have you looked at your initial advance at idle?
Finally, got to spend some time with the GS. Timing is steady at 12 degrees above TDC at 750 rpm with a consistent idle (sometimes it seems like it will cut out, but the cam is probably larger than most, but don't have specs on it - max torque @ 3,400 rpm/max hp @ 5500 rpm). Accelerates smoothly (either low, moderate or extreme load) and 70 mph highway speed is around 2,500 rpm - smooth and quiet. I did not pull the distributor yet to see the mechanical advance setup. A bit concerned I'll screw up the reinstallation and insert it a gear off and blow up my house when I start it. I used an IR thermometer gun on the radiator and got a 30º F drop in temp between coolant going in the top and coming out the bottom. BTW, with vacuum advance (which I do not have), how do you tell how much timing advance you get at what rpm? Is it connected to manifold vacuum or ported? Seems ported wouldn't have enough vacuum (" Hg) for timing, but maybe enough for emission controls...
You don't need to pull the distributor to check the advance stop bushing. Just look under the advance plate, or use a small mirror. The advance stop bushing is retained by a small nut. They are color coded. To measure vacuum advance, you use a timing light with a dial back feature. Rev the engine to the RPM it runs on the highway. Use the dial back feature to measure total advance (initial + mechanical + vacuum). In your case, your total advance would be initial + mechanical. Vacuum advance can be connected to manifold vacuum, or ported vacuum. When connected to manifold vacuum, it adds advance at idle, even at closed throttle. This bumps your advance at idle, which can aid in keeping the engine cool. When connected to ported vacuum, it only adds advance as you open the throttle. Regardless of how you have it connected, vacuum advance disapears at wide open throttle when vacuum drops close to 0. In order for the vacuum advance to add timing, the vacuum must overcome a spring in the canister. When vacuum drops, the spring pulls any advance that was there out.
