I post earlier about issues with slight pinging on tip in throttle while driving - new summit HEI 12 initial 34 3000 and have vacuum advance to ported vacuum (left side port on edelbrock carb).
after doing research and following suggestions on forum, I have moved advanced to manifold vacuum (right side port on carb). 12 initial 34 total but when I hook up advance I get 30 degrees initial and it climbs to 50-55 degrees at 3000. I took it out for quick drive and runs great. I thought though that timing would not climb but drop once throttle opened when using manifold vacuum. Is this timing too high when only 34 with advance disconnected at 3000 but 50+ at 3000 w vacuum advance on manifold.
thanks for any help in understanding.

 

If the engine runs well that way, go with it. Nothing wrong with those timing numbers as long as there is no pinging. You can always limit the vacuum advance if needed.

 

I thought once throttle opened vacuum dropped and I expected manifold vacuum advance to fall off. Is it behave differently in park revving engine vs on the road driving.
thanks

 

I ran nearly 60 degrees on iron head, low compression Olds V8s. Those numbers are fine if it isn't pinging.

 

This was basically a stock rebuild 350 weeks ago mild person cam, 650 edelbrock, rpm intake, stock exhaust manifolds

 

It depends upon how much the throttle is opened. Wide open throttle results in a low vacuum signal, but partial throttle can generate a strong vacuum signal.

Yes, with no load on the engine (in park) the vacuum signal will be somewhat different.

 

You need to mechanically limit the vac advance to 10*

 

I have an adjustable vacuum can, I’ll back out adjuster and see how timing changes.
i need to take it on a longer drive and see how does, around the neighborhood with current timing it really felt good, i was just worried about 50 degree total timing if it would hurt engine
I haven’t dealt w vacuum advance in years - last few builds have been performance/racing and were either locked out timing or initial and mechanical
thanks for input

 

I had a 9 to 1 Olds 350 214/214 .472/.472 on a 110 LSA cam. I ran 22 base and 38 total. It had a 30 degree vacuum can on manifold vacuum. In the 40's at idle and high 50's part throttle. No pinging but had low speed bucking just off idle. The 20 degree vacuum can fixed it but was slightly less responsive at part throttle.