Need some help setting vacuum advance

[ShelbyDogg]

I always run vacuum advance hooked to the manifold vacuum port. All new computer controlled timing setups and efi timing controllers all let you set total timing under load and cruising. If you look at their tables, light throttle, high vacuum conditions let you ADD advance, just like a vacuum advance would, when hooked to manifold vacuum. When light load, high vacuum conditions, some of my total timing was 55 degrees. My efi AFR is set to 15.4 to 1 under light load. It takes an early spark to ignite and fully burn such a lean mixture so you have to have your spark come in early.
Max 36 to 38 degrees total timing is for wide open throttle only.  At WOT, your vacuum advance isn't adding anything if hooked to manifold vacuum.
Your engine will idle smoothly and run cooler with it hooked up and you'll get better MPG.

[Racer57]

I bought a timing light that allows you to pre-set your degrees.

I got in a hurry and didn't check so I don't know exactly what it was before, but after setting my timing at 35 with the vacuum hose off, the car runs crisper/smoother but hotter. City driving 85degrees outside temp was 185-190 is now 195-200. Highway is 185.

I'm going to hook up vacuum hose, set speed at 2,500 and then timing at 55 and see what happens.

[dodj]

I always run vacuum advance hooked to the manifold vacuum port. All new computer controlled timing setups and efi timing controllers all let you set total timing under load and cruising. If you look at their tables, light throttle, high vacuum conditions let you ADD advance, just like a vacuum advance would, when hooked to manifold vacuum. When light load, high vacuum conditions, some of my total timing was 55 degrees. My efi AFR is set to 15.4 to 1 under light load. It takes an early spark to ignite and fully burn such a lean mixture so you have to have your spark come in early.
Max 36 to 38 degrees total timing is for wide open throttle only.  At WOT, your vacuum advance isn't adding anything if hooked to manifold vacuum.
Your engine will idle smoothly and run cooler with it hooked up and you'll get better MPG.

I understand the theory, but my engine seems to complain and ping at highway speeds if the vac advance is in play. I assumed it was because of tooo much advance. I have no surging issues with the vac advance dialed out. Any ideas what other issues I may have causing the surging with vac advance in full operation?

[ShelbyDogg]

I bought a timing light that allows you to pre-set your degrees.

I got in a hurry and didn't check so I don't know exactly what it was before, but after setting my timing at 35 with the vacuum hose off, the car runs crisper/smoother but hotter. City driving 85degrees outside temp was 185-190 is now 195-200. Highway is 185.

I'm going to hook up vacuum hose, set speed at 2,500 and then timing at 55 and see what happens.

Do you know that will happen to your engine at 55 degrees btdc? Do you understand what high vacuum, light load is? Do you know what manifold vacuum is?

[ShelbyDogg]

I understand the theory, but my engine seems to complain and ping at highway speeds if the vac advance is in play. I assumed it was because of tooo much advance. I have no surging issues with the vac advance dialed out. Any ideas what other issues I may have causing the surging with vac advance in full operation?

If you ping, your compression is too high, your octane is too low or you have too much advance dialed in.

[Finoke]

Thanks everyone for all the helpful information. I locked in the timing today and the car is really running well. I'm very pleased 

Its a 383 with an unknown performance cam.

23 deg initial advance @ 750 rpm with 13" vacuum by gauge but set with vac hose disconnected from distributor.
35 deg mechanical advance @ 2500 rpm with 20" vacuum by gauge.
51 deg vacuum advance (5 1/2 turns in on vacuum pod) @ 2500 rpm with hose connected to ported vacuum.

The car starts fine hot and cold. Runs well at all speeds with no pinging.