Spark Plug recommendations?

[WayneLBurnham]

OK, I'm an idiot. I listened to the parts monkeys.

I think they went the wrong way on the heat of the RapidFires they gave me - anybody know the system on those?

Anybody have a general recommendation on plug selection and gap for a stock 350 SBC in a '75 auto with an aftermarket ignition (Mallory HyFire) and lots of decent bolt ons but no great guts, compression or cam?

These guys gave me RF #10's, which were gapped at 0.035". As my last plugs showed a little erosion, but not a lot and no black deposits, I said give me fairly COLD plugs. I altered the gap to 0.055" to make the most of the long spark duration, but a nagging midrange miss is increasing and I caught one reference to HIGHER number RF's being HOTTER plugs - but I couldn't follow it up.

I'm inspecting them tomorrow, but what are anybody's general choices?

Thanks for the input.

[JohnZ]

I'm not familar with the numbers on the later "peanut" plugs, but whatever the cross is to the "45" AC heat range should work fine for 99% of driving conditions; they don't make 46's any more, and 44's are a shade too cold for most normal driving and can have some light fouling problems. Don't waste your hard-earned money on "Rapid-Fires" or any of the other "whizbang" plugs; they won't work any better than ordinary brand-name plugs, regardless of the marketing hype, and I wouldn't go any more than .040" on the gap - I run .035" gap on all my '67-'69 small-blocks, no problems.

[Lucy64]

I agree...I user good old AC 45 in my 64. I do run a bit more of a gap because I have an HEI on my 327. You can't go wrong with what GM used originally.