The 32 is Fords original specification for all of the high performance engines and most of the 4v equipped cars.
The 42 is a hotter plug and was specified for most of the 2v equiped engines.
The reality is that both engines will under normal circumstances run fine with either.
It really depends on how your particular car is driven most of the time.
If it tends to run hot, is tempermental on a restart when it is very hot, doesn't get to stretch it's legs for anything like a mile or two of uninterupted driving with maybe some wide open throttle for a 1/4 mile or so, you would be better off with the HOTTER plug.
The 32 is not particularly susceptible to loading up but it is on the cooler side and if your ignition is a little week, they can foul on you.
You need to read your plugs. The tip, the porcelain insulator and the base.
Ideally the tip shouldn't be black or white but clean with a transparent rust color tint to it.
The insulator should be white, the base clean...and there in lies a tale.
What happened with Motorcraft is another story. They dropped the 32 temperature range entirely.
Then, they rewrote the specs in the engineering charts to show that the 32 is equal to the 42. This of course is not true. They fudged it.
Next what happened was that the aftermarket picked up on the change and reorientated their brands to agree with the "modern" Motorcraft spark plug chart.
Everyone but Champion that is. All other manufacturers say their plug is equal to the 32, which it is not. It is equal to the 42, but that's because of what Motorcraft did to the plug chart.
Champion didn't change their chart. F9Y is the plug range originally specified by Ford, not the F11Y.
If this sounds confusing, it is.
Like I said, the car will run on either. For being stuck in bumper to bumper traffic in 100 degree traffic, the 42 is better.
For track time it is too hot and you may read the plug with these little tiny metal beads on the insulator. Those are aluminum droplets supplied by your melting aluminum pistons.
Actually in my experience a Cleveland in the equivalent of the Boss 351 configuration running on the track should use AF22 plugs.
In all honesty, I haven't run iron heads on the Pantera in 20 years. They are aluminum and run an entirely different series of plugs.
I've got NGK BP5E. If you look at where the temps are for that plug it is a little hotter then a 42. Not near a 52 though. Maybe more like a 45 and it has a wider heat range.
Reason is heads are aluminum and running Weber carbs which can foul plugs at idle pretty easily.
Engine still revs and is limited to 7200rpm.
Sorry for the long story. Try the 42's. They'll probably be ok unless you run flat out on the track?
