KR 428 CJ Spark Plugs Suggestions

[shelbydoug]

The only thing that I can add to this discussion is that normally the size and type of plug that was used was the BF32.

That was in the case of the "high performance" plug application that was cold enough for the design of the ignition system, considering the advance curve, etc.

In the case of the 67 GT500 428, they used and recommended the BF42, which is one step hotter and thus less prone to fouling.


That's what I have and I have not looked at what was used originally in the '68 and up?

I am thinking though that the hotter plug was used because the tendency of the 2/4's with an automatic to be "just a little bit big" for a street car in summer traffic and maybe in testing in Arizona in the summer, the decision was, "let's put a step hotter plug in the car just to be sure?"

In any case, a 42 is going to be too hot a plug if you are going to race/track the car and will act as a rpm limiter to and extent. Look to it to be a 5,000 rpm engine with the hotter plug whereas the colder plug is more of a 6,000 rpm plug.

Does the hotter plug run cleaner? That's debateable? You will see white tips on the electrodes with them though. Dark Greyer on the 32's.

BF32 is what the 68 and 69 CJ used from the factory. There is not going to be any 6,000 rpm happening with the hydraulic cam in the stock 68,69/70 CJ engine.

The point being that the heat range of the spark plug does effect the rpm POTENTIAL of the engine.
Between those two plugs, the BF32 has more rpm potential.

The actual rpm ability of any of the Ford FE engines as originally built by Ford has always been debated. I wouldn't expect any of that debate to be settled here or on any chat line, only on the race track. I wouldn't pretend to be the expert to determine those limits. That isn't me. Others may feel differently.