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Anyone have any experience with Pertronix ignition?


ledfootslim

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To clarify a bit, "point bounce" refers to the tendency of a points system to become inefficient at high RPMS (typically past 4,000 RPM). The older method to alleviate this is the use of multiple point distributors, typically dual point distributors.

Even when multiple points are used, mechanical inefficiency can cause problems. In the early 1970's, BSA/Triumph raced a 3 cylinder motorcycle which had one point per cylinder system. The points were opened by a cam on the end of the exhaust camshaft. At racing RPM's the runout in the cam was found to be enough to make the timing erratic even with the 3-points system. The engines were misfiring at around 6,000 RPM. The solution was an electronic system which was more tolerant of the camshaft movement and thus eliminated the high RPM misfire.

Engines which operate in the lower RPM range (up to 4,000 or so RPM) work fine with single point systems, and the benefit of dual point systems generally appear around 4,500 RPM and up.

Electronic (reluctor based) breaker systems tolerate a lot of slop and provide consistent timing throughout the normal RPM operating ranges.

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Can you further explain how a dual points system can reduce point float? The distributor cam still travels at the same speed no matter how many points it is driving.

 

In 1969 I raced a BSA Rocket 3 at Bonneville. My engine was internally stock with exhaust modifications and re-jetted carburetors. I personally never experienced point float but others possibly did. I agree that an electronic pickup should eliminate this issue.

 

12-18-057.jpg

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Can you further explain how a dual points system can reduce point float? The distributor cam still travels at the same speed no matter how many points it is driving.

 

In 1969 I raced a BSA Rocket 3 at Bonneville. My engine was internally stock with exhaust modifications and re-jetted carburetors. I personally never experienced point float but others possibly did. I agree that an electronic pickup should eliminate this issue.

 

12-18-057.jpg

Sure. The problem causing bounce with mechanical contacts is the number of times the points must open per distributor revolution. In a six cylinder car with single points, the contacts open six times per revolution. In the same car with a dual point distributor, each contact set opens 3 times per revolution, thus reducing the bounce effect when the contact points close.

It was Doug Hele's group at Daytona in late 1969 I believe that determined the triples had the points problem. Eventually they got it fixed and won a few races, and Jim Rice's triple flat tracker had the conversion as well. Personally, I love the triples - great bike.

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The dual point setup I used to have opened each set of points once for every cylinder. Eight cylinder engine opened each set eight times. The points were offset just a bit so when the first set was closing the second set was already open, giving the coil time for full saturation.

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I have been running dual points in my Mopar flathead 6 cylinder engine for several years. Both sets of points open once for every distributor revolution. Due to the way the point mounting plate is configured with an offset when one set of points opens while that set is still open the second set of points opens. Then the first set closes and soon thereafter the second set closes thus increasing coil saturation time because of the overlap. This has no effect on reducing or eliminating point float. And at the low RPM's most flathead 6 cylinder engines run point float is normally not a problem unless the point spring is defective.

 

The only way what you describe could work is if a special distributor were used that had only 3 cam lobes or the distributor were geared to run at 1/4 the crankshaft speed. I have never seen a distributor configured as such.

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Both Autolite and Mallory made dual point, 4 lobe distributors for 8 cylinder cars, and Ferarri and some other engine manufacturers used 3 lobe distributors for both inline 6's and 12 cylinder cars.

Here

http://www.ferrarichat.com/forum/vintage-thru-365-gtc4-sponsored-vintage-driving-machines/180912-advantage-3-vs-6-lobe-distributors.html

is a pretty good online discussion of dual point, single point, dwell vs. bounce in distributors.

Edited by jeffsunzeri
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Both Autolite and Mallory made dual point, 4 lobe distributors for 8 cylinder cars, and Ferarri and some other engine manufacturers used 3 lobe distributors for both inline 6's and 12 cylinder cars.

 

I remember working on a Dodge Super Bee way back when, it had a 4 lobe distributor with two sets of points and unfortunately, that is all I remember about it.

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I don't think I had a point bounce problem with mine. According to the tach, it made regular runs to 8k rpm. I did have an occasional problem with valve keepers and retainers though.

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  • 5 months later...

Have the Petronix on most of our old Dodges-about 20, 0 problems. Plus have customers using them with no problems. Have HEI on of our 34, that is the best set up. Better fuel and performance but more expensive.

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