Anyone have a recipe to achieve the following HEI curve?

~ 12-14* max mechanical adv
mechanical adv not starting until at least 1300
mechanical all done between 3000-3500

It looks like it's pretty difficult to keep an HEI from starting the mechanical advance below 1200, and then also to limit the mechanical advance total to 12-16*.

I know the MSD pro billet setup has little travel limiting bushings and I could fairly easily do this on the MSD, but I have an otherwise perfectly good HEI that already has the MSD specialty HEI module..don't want to toss it unnecessarily.

reasons are big cam, solid roller lifters, 900-1000 rpm idle, the usual culprits. With the cam I have, it likes around 20* initial at idle at 1000rpm, so I only need 12-14* or so to get to my total desired timing (32-34 with my small chamber fast burn heads).

the curve i have now is playing in mechanical advance territory at idle and making tuning difficult.

 

The best advice i can give is play until its right.

 

You limit the total mechanical advance mechanically, not with spring stiffness.

That's done by opening or bushing the advance slot, as required.

 

On a stock HEI the geometry between the tails of the weights and the centerplate is the only thing that limits the total centrifugal advance. The slots don't do anything on a stock HEI but provide a place for the pins to stick through. There are not many HEI centerplates that give only 14* advance. I have one and I believe it's number 499, but I don't have it in front of me. Doesn't matter- you'll never find one yourself and I can't imagine how you'd order one from GM. Maybe there's some speciality shop that caters to the HEI that might have what you need, but I know of no such place to order parts like this.

Many have reported that the Summit brand replacement HEI has a centrifugal setup that only gives 14* advance, but I doubt you could get the centerplate/weights from them without buying a whole distributor. Maybe it's worth a call- I'm sure they don't manufacture it themselves and maybe they will tell you who does and then you can track them down on your own.

Final option is to modify your existing distributor and build in your own stop. Bushings won't work- the slots aren't wide enough for them. You'd need to find somplace you could weld on a small piece of metal and provide a positive stop for the advance plate. It's location would be critical and if you got it wrong you'd have to grind it off and try again.

 

Did I do a brainfart again and mix up old Delcos and HEI's?



From what I've seen and been able to gather about HEI advance kits, they're made by Mr. Gasket and others like Summit are allowed to put their name on them. The only thing I've ever used from one of those kits is the springs.

(And, for the record, with mine I need more mechanical advance in order to get proper total w/o too much initial. It hasn't bothered me enough to do something about it, though.)