Steve Straus

I have my MSD installed and working now, and as the instructions say, the advance springs are very stiff. I have lars's distributor tuning doc, I'm just not sure if it's applicable to an MSD. Before I experiment with different springs and advance stop bushings, I'd like to hear what your experiences were.

Thanks

Vetterodder

My setup is in a SB but I think it would be a good start for you. I used the silver bushing (25º limit) and the softest springs (silver) and set it at 37º total (12º initial). A heavier car or taller gears might do better with a less aggressive curve (one silver, one blue spring). With your 468, I would think it should handle a pretty aggressive curve. If you're running a big cam, you might do better with a B28 vacuum advance can as it wil deploy at a lower vaccum.

Steve Straus

I had a problem with my Vacuum advance coming in too soon, I want to build more cylinder pressure, so shouldn't I want it to come in at a higher rpm?

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Steve

Larry B.

Steve... I played around with mine for quite a while and the best I could do was 8 deg initial. 28 TOTAL at 3000 and NO vacuum advance. Even then on any fuel except Amoco 93 I get a little pinging on real hot days. Anything close to SB specs is too agressive for BB's

69ttop502

Steve, on my 502 before I tore it apart I was running the lightest springs with the 28 degree bushing with 10 initial. It ran perfect and I checked it with a dial back light and all of it was in by 2400. No pinging on 93 pump gas but that motor was a 8.75 to 1 mellow little devil. Bill.

73 LS-4

There's so many variables here it could make your head spin. Normally the higher the compression the less advance it will tolerate with pump gas. The whole idea of advancing the timing is to have maximum cylinder pressure 12.5 degrees ATDC. My engine being a low compression Rat, I can run a pretty aggresive curve with 93 octane fuel, becouse heat buildup in the cylinder becouse of high compression is not much of a concern and the bore is large therefore it takes a little more advance to get the flame front complete across the entire bore compared to most smallblocks. Remember a flame front will travel at a given speed and this won't change much, therefore the more rpm or the longer the distance it has to travel the more advance you have to give it to have peak pressures at 12.5 ATDC. Now if you throw high compression in there you have another factor of avoiding preignition, as a gas is compressed as you know it builds heat and the more you compress it the more heat it builds and an octane rating is simply the resistance of a gas to spontaneously ignite under heat,it has nothing to do with BTU's per gallon. As a lot of people on here find out, the engine preignites at some point before optimum timing advance for their engine, therefore they run the curve slower then is optimum for engine power in order to drive it without damage on pump gas. Now when they switch to racing gas then they can run the curve that is optimum and get full power. Now with aluminum heads you can get away with a little more compression on pump gas since the aluminum is a much better heat dissipater then cast iron. What it all comes down to however is trial and error, go lighter one step at a time and run the same gas all the time if you can so you know what it will tolerate and there isn't another variable to setting up your curve. I personally run 12 initial 38 total, but I think we are running far different animals here, I'm only 8.25:1 (as far as I know, haven't been in there) with a mild cam.

:cheers:
Pat Kunz

Steve Straus

Thanks for the responses. (Esp Pat).

I'm running 10.5:1, so I should probably experiment in the mid-range of the springs. I'll play with it.

Thanks


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Steve