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General Tech Distibutor Caps

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RLBaird

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There are 2 distributor caps available for my 64 herald. One for high compression and one for low compression, please explain??
 
The one for high compression is more expensive. To me, no conceivable relation between compression and distributor caps. Are there different compression ratios for Heralds? Doubt it.
Bob
 
In theory, the higher the compression, the more voltage it takes to jump the spark plug gap. The higher the voltage in the system, the greater the chance of arcing elsewhere in the high tension system....like within the dizzy cap. I don't know anything about Heralds....
 
John is right about the theory. There is a principle called Paschen's law that would govern, but I am not a physicist or mathematician. Sadly, we would probably need a working Ouija board to find an authoritative answer on BCF (it's the sort of thing our friend TR3 Driver would have known). I have never found the air gap between rotor tip and plug wire tower to create a problem in practice on any engine. In any event, the spark (potential energy) applied by the coil wire to the center of the rotor, as a practical matter, has to go to ground somewhere. Absent a defect in the cap or plastic body of the rotor (like a crack or carbon track), any distance within the distributor from the rotor electrode to any ground other than the plug presents many times greater resistance than the rotor to plug wire tower air gap ever could. I think that the difference between the caps you are looking at is either promotional only or is an implicit statement by the seller that they are stuck with a group of defective caps. BTW, if you Google "high compression distributor cap", you will get zero relevant hits.
Bob
 
Last edited:
RLBaird said:
There are 2 distributor caps available for my 64 herald. One for high compression and one for low compression, please explain??
Click to expand...
Outside of the US and in some areas of the world there certainly were low compression engines. My herald originally had a low compression engine. When I rebuilt it I put flat top pistons and had the head shaved so it became a "high" compression engine. If the cap is for the correct dizzy type it will work perfectly fine. Maybe 50 years ago there were actually different versions.... but today they will all be basically the same other than quality issues. Note that there are different quality ROTORS and a low quality rotor will cause problems. The best is to find an original old Lucas rotor in good condition.
 
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