Went to pick up plugs for the 351C and asked for the AF-42s, and was told they're obsolete and interchange with the AF-25s. I hate to ASSume with the big box chains, so thought I'd check in here real quick before changing. Thanks.
[QUOTE=dalorzof;3998637]Autolite site lists various -42 plugs, no AF prefix. Would assume the AF-42's are obsolete. Forget the OEM spec for my 68 390, but a similar story... 40+ year old plugs no longer made.
Don't have a solution on the 351C, but for the 390, they were the BF-32 plugs originally.
A VERY close replacement is still available today - Autolite Racing AR33. They are ever
so slightly colder in heat range. If the engine & ignition are in good shape, you won't have
a problem. They are $3-something a plug but if you're running a 390 at this point in time,
the price of spark plugs isn't your greatest concern.....
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For your cleveland go ask for Autolite number 25 no letters or prefixes that is the standard plug, If you have high compression and hotter cam and want a colder plug ask for Autolite 24. If you have a MSD or other high energy ignition you can open the gap up to about .40 or .45
Thats what I use and they work, If you want a race plug its Autolite A133
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