Recurving pre-1969 stock points distributors

Schurkey · Jan 28, 2024

Overly-LEAN, I might believe.

1968_GS400 · Jan 29, 2024

Bigpig455 said: ↑

I remembered this thread when I was reading an Denny Manner interview in the August 1971 edition of Speed and Supercar. Denny suggests that early timing is a crutch for an over rich condition, and he found his factory settings actually made more power. Here's the article..

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This was back when the engineers at GM knew what they were doing.

Great article.

87GN_70GS · Jan 30, 2024

Jim Weise said: ↑

And don't put all the advance in at 2500.. that's an old wives tale that was a started by someone who did that, and their car ran better because it masked some other tuning/combination mismatch problem..

I stumbled upon this fact by accident... about 8 years ago, I was just finishing a dyno session on a 550 HP Stage 2 street engine. There was a tight window to get that engine finished and on the dyno, so I had just taken the MSD billet distributor out of the box and installed it, with it's big coil spring like advance return springs and all. Session went well, it came with the 12* bushing in it, so that was fine... right at the end of the session (customer in attendance) I said " here, now we will get that advance in earlier and makes some more power.

So I pull out the big heavy springs, and but the middle size silver ones in.. Did a pull.

It looses power.. substantial HP and Torque.. 8-10 numbers each way, as I recall.

After some discussion in the dyno control room, as to if that was a real result of some type of fluke, we decided the best way to find out is to put the big heavy springs back in it
and pull it again.

Did that, the power cam right back, you could lay that sheet right down on the one before I fooled with the distributor.. numbers were right on.

I noted that, and the engine went back to MI with it's owner..

Over the next 8 months, I repeated that test on 4 different engines, all with very different builds, and the results were the same every time. Not one of them wanted the spark advance that quickly, it cost varying amounts of power across the build, but that early advance never helped.

Having it all in by 3800-4200 was the range that most of those motors liked.

JW
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We also noted the same thing while Dyno testing and playing around with timing. Our best power numbers, hp and tq, were obtained with a curve that came in late. Even later than what Jim found, 5500 rpm. And we ended up with more timing than what is usual.

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Recurving pre-1969 stock points distributors

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