I ordered a streetfire dist. for the chevelle last night. I understand it comes with 20* mech. adv. @4000rpm I also bought the curve kit. From what I understand most motors like 36* adv. This is a stock flat top 454 with peanut heads, RV cam. So Im thinking of using the curve kit to get 24* mechanical and 12* initial. and use the vacuum advance.
The car has a Mallory magnetic mechanical distributor right now. We put that on to replace the stock HEI that only had about 6* mechanical adv. and it really woke the motor up. But everything I read suggested for everyday driving you really want a vacuum advance. thanks jim

I'd leave the 20º bushing in and run 16º initial. End result will be the same but idle and off-idle response will be better. You'll need to experiment with the springs to see what your particular combination likes. Ideally, you'll be able to get your total all in by about 3k. I agree with using vacuum advance. It may need to be adjusted depending on how fast it comes in and how much it gives.

Stock or very mild cam? No way do I want 16 degrees of initial advance--you'll have fun getting it to idle slowly enough. Then you've got to throw the vacuum advance onto a ported source to cut the advance at idle. No thanks.

Stock cam = low initial timing, lots of centrifugal.
Wild cam = lots of initial, not much centrifugal.
Either way, you'll adjust the total timing--and the rate it advances--for the individual engine.

Add as much vacuum advance as you can without part throttle ping or miss; and "probably" connected to manifold vacuum--but try ported and see what happens.

Last starter on the motor, didnt like over 12*. Hard cranking, but the new starter with the Flywheel, seems to spin over fine. Jim

Even a non stock afermarket mild RV cam will likely need 16 deg base timing as was already suggested above.

I have installed a few mild rv cams for people over the yrs in sbc & bbc and they all like approx 15-16 deg base timing . So run 20 deg mech in the dist all in by 2800-3k rpm and that should be a good place to start with a 36 total timing all in by 2800-3k rpm..

Also run a vac adv too hooked to full vacuum too,it worked fine every time i ran that setup with mild rv cams.

Scott

I just bought the same distributer and same optional advance package, put the advance kit in, ran it, stared at the timeing light and was totally frustrated, the mechanical advance did nothing up to I beleive abt 2,500, then like a light switch it jumped about 10 degrees, and that was it, totally bogus, took the distributer to a very sharp guy, we put it in his distributer machine and he said the weights where too liight & springs too strong, went back to the stock componants at it was pretty good, advance started abt 1100 (we did not want it moving at idle) then it advanced about 18 more by 3500, not 100% perfect but very workable.
BTW I have 9.6 to 1 compression and that "Jegs starter", you can crank the initial way up into the 20-30 range* and it spins up effortlessly. After having that piece I will never leave town with a GM starter!
*It was in that range on initial startup, my combo is closer to 14 initial, then with vac & centrifical all in its mid 50's, everything is happy but the tires

Well I just dropped the dist. in. I havent had a chance to hook up a light to it, but it fired right up and seemed to rev real quick! I went with the light springs, Suppose to have 24* at 3000. Im going to start at 12* and see how it runs this weekend. Jim

Well I just dropped the dist. in. I havent had a chance to hook up a light to it, but it fired right up and seemed to rev real quick! I went with the light springs, Suppose to have 24* at 3000. Im going to start at 12* and see how it runs this weekend. Jim

Jim, just a couple of thoughts, but look over the advance curve from MSD that comes with the kit. With the lightest springs(copper ones) you will start to see 8* of mechanical advance at 500 rpms. Meaning that 12* initial timing might really only be 4* initial and 8* of mechanical.

This had me stumped until I really looked over the advance curve, on my street fire... I would just set the total to 36* and let the initial fall where it wants.

So on my motor if I put the light on it at idle about 900 rpms, the timing is right at 20*, which will be the 12* initial and 8*mechanical coming in at 500 rpms.

Again this had me confused when I first installed the distributor because I always set total timing first, and could not understand why with 36* total timing, why I was seeing so much timing (20*) at idle. It is all do to how fast that mechanical advance comes in with those copper springs, sorry if I am repeating myself :):):)

ADVANCE CURVE FOR THE PN 8428 GM HEI WEIGHT AND SPRING KIT
500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000 6500 7000
8 12 16 20 22 24 24 24 24 24 24 24 24 24
0 8 10 14 16 18 20 20 22 22 22 22 22 22
0 0 8 10 12 12 14 14 16 16 18 18 18 18

Im wondering if I should go with the medium springs instead? I'll get out the light and see what happens this weekend. Jim

Yup,common problem having the mech adv partisally activated when setting base timing whihc s why i alsways suggest low idle when setting base timing to avod the mech activating and upsetting the base timing setting resulting in significantly retartded base timing.

If your running a perf cam which you likely are even a mild one needs approx 16-18 base timing and hot ones can use 20+ base timing at times.

So with that said either you or a shop should 1st set up the mech adv in the dist for 18 deg in by 2800 rpm.

Then set base the timing to 16-18 at a low idle speed with vac adv unhooked to prevent above mnetioned problem.

Now 16-18 base timing + 18 deg mech in dist will = 36-38 deg in by 2800 rpm which is a good starting place for a perf ign curve .

Also,esp for street us have a vac adv installed on the dist thats full activated at 2" below the lowest idle vacuum with auto trans in gear. That vac adv should also give an additonal 14 deg timing for better idle ,better throttle responce,better fuel economy,and cooler running motor . The vac should be hooked to full vacuum all the time,not ported vacuum in this typ application..

If your not running a vac adv and its a street motor then you should really get one or your leaving having a crisper feeling motor and some fuel mileage on the table.

Scott

Im wondering if I should go with the medium springs instead? I'll get out the light and see what happens this weekend. Jim

Jim I do not know your cam specs but I tried the medium springs on my motor(383) that only had about 220* of duration and it ran like a slug. As soon as I installed the lightest spring I instantly had a smile on my face...

You won't be disappointed with the lightest spring, just set the total timing to 36* and go for it...

I think you will like it, plus the initial timing will still be 12* when the motor is cranking and trying to start. You will not see the mechanical advance until the motor is actually running. Someone correct me on this if I am mistaken....

Keep us posted on the progress!!!!!!

My car has a "RV" or real "mild" cam, and I set initial to 16° and 36° total. I added almost 20° vacuum advance to ported.

Yes, my starter would slow crank after the additional timing (initial was 0°). So I bought a high torque mini.

Don't leave timing on the table! My car rips now (well for a weak 350).