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Blued and Painted

3505 Posts

Posted - 30 Aug 2012 :  8:46:54 PM  Show Profile  Reply with Quote
How much mechanical advance could i expect out of the stock point type GM distributor? Are there some mods that should be preformed? Thanks, B&P

Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.

Edited by - Blued and Painted on 31 Aug 2012 10:32:36 AM

Crazy Horse

1442 Posts

Posted - 31 Aug 2012 :  6:39:12 PM  Show Profile  Reply with Quote
I got 30 degrees with the stock on off my 74 FBird.

The one thing I did find with mine is that the bushing that goes over the limiting pin was gone and I had too much mechanical advance.

I found a thin piece of vacuum hose(I actually believe it was WW Fluid hose) that fit over the pin that worked out great.

And I ended up using one heavy spring and one medium spring to control the rate of advance.
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Crazy Horse

582 Posts

Posted - 18 Sep 2012 :  9:58:50 PM  Show Profile  Reply with Quote
The Motors book should list the advance. Buy a spring/bushing kit from Summit or Ames. I welded mine up to limit total even with a bushing. Im at 12int and 32 total. If you use a machinist ruler and measure the original gap you get a degree to thousands ratio. I don't remember the exact measurement, but say a degree would equal .010 of an inch. You can get very close to your goal on the first try.
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Crazy Horse

1442 Posts

Posted - 19 Sep 2012 :  06:44:30 AM  Show Profile  Reply with Quote
I got 30 degrees with the stock on off my 74 FBird.

Turns out I can't add or subtract. I went back and looked at my notes.
Mine actually advances 21 degrees mechanically.
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Bill Boyle
Horse Feathers (Charter Member)

5092 Posts

Posted - 31 Jan 2014 :  09:21:38 AM  Show Profile  Visit Bill Boyle's Homepage  Reply with Quote
I spotted this old thread and thought it would be one to update with a recent experience.

A fellow enthusiast sent me his points distributor out of his 70 GTO. I ran a test on it and recorded the curve. I was amazed overall of the good condition of the piece but the stock curve was slow. In fact it never plateaued. The unit was run above 6000 rpm but the springs allowed it to slowly climb all the way to that rpm. This was the first distributor that I've run across that did that. The amount of mechanical climbed to 30 degrees.

The dwell was lowered from 31 to 30.3 and the combination of new springs altered the curve so that it was all in at 3000. The mechanical was stopped at about 24 total degrees. The unit will use manifold vacuum and was set up that way.

When the owner gets this back into his engine, he will really see a performance difference, I'll bet on it. An adjustable vac can was included as well to work with the mechanical curve and to keep it all down and right for his street performance.

FYI, this distributor spun smoothly past 6000 with no misfiring. Point distributors are still practical on our cars that see limited use. That's my read.


"Dedicated to keeping the classic Pontiac engine alive."

400 bored +.030, forged TRW pistons, ported 62 heads, Hedman headers, 2.5 SS dual exhaust X Pypes, Comp 276AH10 cam, Scorpion 1.65 RR, 850 Q-jet, stock intake & tuned HEI; original owner.
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Sitting Duck

1531 Posts

Posted - 31 Jan 2014 :  11:01:07 AM  Show Profile  Reply with Quote
I had my original points distributor rebuilt a few years back also. I noticed it was putting way too much mechanical advance in at higher RPM. The weights' stop was apparently worn out. I think it was adding 8-10 degrees too much advance at higher RPM.
Another thing I RARELY read about concerning points distributors is running a higher weight points set. I run a 32 oz. set in my GTO. I believe factory was around 22 oz. The higher the oz. rating the "stiffer" it is,and less likely to bounce at higher RPM. I've had my 400 over 6000RPM a few times,and shift around 5800 or so at the track,no points bounce.

71' GTO Original 400 M20 3.23 posi
13.95@102.1 MPH on street tires

Edited by - 67drake on 31 Jan 2014 11:03:31 AM
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