Posted in SBC section but looking for more info...

I am changing distributors and coils today but wanted to know what everyone thought.

When engine was brand new the only thing unchanged was the distributor, MSD6a, and Mallory coil. The truck ran like a champ and had incredible power from idle to redline. Now all of a sudden it sputters from idle to 1500rpm and doesnt rev freely to 5500, redline from engine builder is 6500. Engine when new ran high 12s in the 1/4...now runs high 13s with 4000 miles. I have changed timing many times with no change in power. The timing light does sputter over 2500 rpm at close to the same duration of flash at idle. Some people tell me the MSD box is burnt up because it sat for 2 years before being used again. Others say the distributor is the problem or the coil. I have changed everything else on the engine except these things but today I am putting on a Mallory HEI unit and not using the MSD box. I wanted everyones opinion on possible fixes or support that this will solve my problem. Thanks for your time and patience.

I've never had much luck with MSD box's on the street, prefer the "plug and play" distributors with the HEI coil. The MSD's seem to be a bit too sensitive to heat and vibration for continuous street use on a daily driver, JMO. I'm sure others have stories of how their MSD has been trouble free on the street for umpteen thousand miles, guess my experience with them is not as good.

Well this particular box has had close to 20,000 miles from my 2 different engines and no telling how many thousands of miles from the previous owner who drove it for 3 years. I guess its worn out. The Mallory HEI will be on tonight. I have read about different places to plug in the vacuum. I guess I will used the one above the blades because the one below pulls too much vacuum advance. I just want to get my truck back to being fast instead of bogging from the start and running out of breath up top. Thanks for the help. Any other stories about experiences with MSD boxes are greatly appreciated.

Well for starters I put in the HEI tonight but its definitely off a tooth or two because it fired right up but popped and sputtered. Also the coil I got says from 4000-7000rpm. I talked to some mechanics and they gave me mixed advice. Some say it wont work well in any other rpm but that and others say that it will work just as good as a regular coil but better between 4 and 7k. I looked online and it says I can use the Mallory Proform box, which I have from the old setup,in conjuction with this 4000-7000 coil but I dont want to unless I have to. Any advice is appreciated.

I'm a tad surprised to read Dave has had problems with MSD. But it can certainly happen. MSD runs all their boxes pretty severely then heat soaks them on the shelf and then re-tests prior to packaging for sell. The electronics are all epoxy impregnated to minimize circuits being mechanically affected by vibration (and to hide their proprietary design!).

I ran a 6AL box in my '68 427 Vette. The box was under the hood attached to the wheel well and believe me it got the crud shook out of it and (Austin Texas) let's just say it got plenty hot in there also!

I replaced an HEI with it at that time and was pretty darned impressed that I could actually tell the difference in how much better the engine performed with the MSD.

But problems can always crop up ..................

Regards, Kitz