How much advance is too much for moderately built 390 in a 67 F100 shortbox.? Motor is bored 0.030 over, Gt heads and cam, Edelbrock streetmaster manifold, headers, Holley 670 Street Avenger carb, MSD 6A, 3.55 gearsm, 4 speed.

I just installed new MSD pro billet dist. which comes with different springs to recurve the advance. I removed the 2 heavy springs installed to 1 light and 1 moderate spring. I presently have the initial advance timed at 14 deg. BTC and total advance is around 50 deg. at 3000 rpm.
Haven't heard any pinging under load and it has lots of jump, but wonder how much advance can a FE stand. I don't want to hurt anything, like a piston or valve.

 

FE engines, regardless of the CID are pretty much limited to a total mechanical advance of 38° (initial + whatever the advance curve cranks in). Vacuum advance is on top that but is only there under light load conditions. Whether you hear it or not, if you have 50° cranked into it, you are gonna hurt the motor.

 

It doesn't make sense. I installed the silver bushing in the MSD dist. that is supposed to restrict the mechanical advance to 25 deg. at around 2500 rpm. Add the vacuum advance of 14 deg. and i should get a total of 39 deg. The harmonc balancer is new with timing marks to 60 deg. Don't understand why I'm getting 50 deg. at 3000 rpm.

 

The MSD type ignitions can cause some timing lights to malfunction. It could be a timing light problem, try a different light. Also the vacuum advance does not figure into the total advance you are trying to achieve, because it is only present under light load, part throttle use. You need to add the initial and mechanical for the total advance.
Are you disconnecting the vacuum advance when checking the total??

 

Always check timing with the vacuum disconnected and plugged. You have to check the initial first, then total mechanical (38°) and the vacuum will be on top of that and I've seen motors tolerate 50° with the vacuum on top of the mechanical advance. I prefer to keep it a little less at around 45° plus or minus 3°, but then that's just me.

 

Thanks for the input guys. I played around with the timing some more today. I installed the black stop bushing in the MSD distributor which stops the centrifugal advance at 18 deg. Add the intial timing of 14 deg and the total is 32 with the vacuum line to dist. plugged. With the vacuum line connected it adds another 12 deg. for a grand total of 44 at 3000 rpm. So is the total advance now 32 or 44?

If I go any less than 14 on the inital advance it has a stumble aff idle & I get a backfire thru the carb, if you hit the gas to quick, ecspecially when its cold. I 've mannaged to lessen the problem by putting the 2 lightest springs (silver) on the centrifugal advance in the dist. so centifugal advance starts in just off idle, but I think there is an issue with the carb. I don't know if changing the acellerator pump cam to alter the shot will cure the off idle stumble. The carb has #31 squirter in the primaries