Hey guys, finishing up odds and ends on my build and wanted to get a better idea of what I'm dealing with for timing. I'm running a HEI Streetfire distributor with a vacuum advance and don't have the money for an msd box.

I just want to get a good idea of a) how much initial and mechanical timing I should run b) should I use the vacuum advance? And I've also heard of people modifying the vacuum advance to function as a boost retard, but I've never messed with ignition curves, limiting mechanical advance, and messing with amount of vacuum advance.

Some insight would be much appreciated

 

id go with about 10-12 initial about 8-10 deg of mech advance, then have the vac advance give you some timming in cruise

 

Ive had decent luck with stock HEI's up to about 21 lbs on E85 (0.025" gap) (missed if i tried higher...wasn't sure if it was valve float or spark power). I simply locked the centrifugal and used the vacuum advance to bring up my cruise advance....ported or manifold worked depending on the combo and what it was "locked" at without vacuum advance.

On my combos (E85) i usually had the timing locked between 20-25* (conservative to start out with) and had about 20* of vacuum advance. Depending on your combo (im guessing here....premium pump fuel, less than 9:1, automatic, not a stock converter, mild cam) starting at 22* and 5 lbs of boost or less with 20* of ported vacuum should get you a decent starting point. It will likely want more timing...but always best to start low

 

Thanks for the quick responses guys, always somebody who has the answers on here haha.

 

I was running 15 initial with another 8 mechanical. However once i went from 7psi to 11psi...i had to dial it back. Now I am around 10 intial and 5 mechanical. I have tk check cuz I been moving it around trying to sort out another unrelated issue.


Using a procomp unit that I bought for $35

 

The Modules in the Street Fire HEI are junk many reports of erratic timing. Check yours with a light at rpm and replace as needed.

 

I wouldn’t get wrapped up in the great timing debates. Zero reason to run timing above 15* till you get the combo dialed in on low boost. I’d Lock it out at 15* with zero mechanical advance and leave it the hell alone until you get the AFR and boost/plugs where you want them. Once that’s sorted, slowly advance the locked out timing a degree at a time and watch the plugs close. Once you know what the engine wants, then setup your curve with a box or mechanically if you are confident.