Limiting Mechanical Advance

[mainejohn]

So i have realized i have to much mechanical advance, my intial timing seems good around 18 degrees, then i add 24 from my jegs hei dizzy and its going to ping like hell when i get on the road!!!!! How do i limit it to 13/14 dergrees? any diagrams would be great!!

 

[FatnLow]

Any instruction sheets from Jegs? What model is it? If it is like a standard gm you would have to weld or modify the plate so it can't give as much. Some dizzy's have adjustable pieces you can insert to limit this. You may just have to back off initial to 14.

 

[JONESYFXR]

I'm just shooting in the dark, but I'd say a combination of different weights and springs. You'll probably have to plat with it (Your Dizzy!!!!), till you get it right.

Hope this helps.

GOOD LUCK!!!!

 

[COPO]

Why not use an adjustable dizzy vacuum pod. http://www.summitracing.com/parts/ACC-31034/

 

[Twisted_Metal]

^That only modifies the vacuum advance.
Under heavy load or WOT, there is no vacuum advance. (It's only initial and mechanical advance.)

 

[mainejohn]

jegs part model is 40005, jegs said the recurve kit doesn't reduce mech. advance, it just changes the time it comes in, maybe they are wrong and they didn't send any instructions with it this must be a common problem with so many sbc's out there.

the reason i want to limit it because many people told me with my cam-(488 lift 234 duration @ 50) that the dizzy i got will not work and it will have to be recurved.

 

[DesmoEd]

this must be a common problem with so many sbc's out there.

Thats one of the benefits of running an MSD. They are very tuneable and come with 4 different bushings that let you limit mech adv to either 18, 21, 25, or 28 degrees.

You set what ever initial you want - depending on ported, manifold, or no vac adv - and change the springs to control how fast mech advance comes in. The bushing controls the total mechanical limit.

EX.........setting 12 deg initial plus using the blue 21` stop bushing will give 12 + 21 = 33 degrees mechanical adv at 2900rpm with 2 blue (light) springs

here is some reading info if you are interested

http://www.msdignition.com/instructions/Products/Distributors/85551.pdf?terms=85551

 

[EricsZ28]

Now you know why people buy MSD pro-billets. They have limiting bushings that you can swap out to limit the mechanical advance. Piece of cake. EDIT - DESMOED beat me to it

With my old HEI, I inserted a screw into the mechanical advance mechanism to limit the travel of the mechanism. I ground one side of the screw and rotated it (like a cam) until I got it dialed in (well, at least close, lol). If you google the topic, you'll find some stuff out there on it...

Have fun!

 

[FatnLow]

John you just need to try it out on the road and see how it works. Before you go and do major mods I would give it a test run. Your motor may like more advance.

 

[mainejohn]

okay i will road test first. so should keep advancing till it pings going on the the road and giving it full throttle, if it pings back off a little and try again. Correct? should i do all this with vac advanced plugged?