I just installed a Pertronix II and Flame Thrower II coil on stock 1972 350ci 4bbl. The instructions for the Pertronix II say that it is typical, but not required, to increase the spark plug gap .05 over stock setting.

I believe that the stock plug gap is .040. I will be installing a set of new Autolite plugs (I think they are "86" plugs). I plan on setting the plugs to .045.

Does anyone have any opinion on the plug gap that works best with Pertronix II/Flame Thrower on a stock 1972 350, 4bbl? Thanks.

 

Typically people run .035 spark plug gap.

 

I did this conversion to both my 70 and 72 cutlass cars. both cars i got the petronix coil and plug wires also, both cars run great and i gapped them both at the factory gap settings. If anyone found it works better to open up the gap id be interested in that info too

Greg

 

I have always gapped mine at factory specs too, and seem to remember reading somewhere that you would gain nothing by changing the gap, and might even hurt. Pertronix is not designed to increase performance. It lets your car run like it has brand new, correctly adjusted points all the time. I did discover one problem with the Pertronix set up though. My car ran fine for so long, I completely forgot about my spark plugs. I dug through my files and realized I last replaced my plugs in 2006...over 30,000 miles ago. The falloff was so gradual that I didn't notice it until recently, and was shocked to see how old my plugs were. With points, it would have stopped running by this point.

 

I set mine at .038 -

 

What gap does petronix recommend?, if they don't have any information I'd suggest leave it as .035.

Roger.

 

What I read in the Pertronix installation instructions was that although not necessary, it is typical to increase the factory reccomended gap by .005

 

I run both my cars at .040 with the pertronix.

 

Consider the coil you're using. With a stock or near stock replacement coil, stay around .035. If you use a higher output coil such as the PT FlameThrower or an Accel, you can usually get away with opening gap to around .040, possibly even .045. Some experimentation may be in order, as the more powerful the spark, the more gap it can fire across. Bigger spark can theoretically ignite more fuel for more power and more complete combustion.

GM HEI coils are designed to fire a .060 gap. They started out at .080 but quickly realised that was stretching it and released a tech bulletin to set plug gap at .060.

 

Well, you have about 6-8 opinions so I will add another. I use 40. I doubt you will see any difference in 35 and 40.