Correct C1 FI spark plug?

[Keith R.]

I've looked at archived postings regarding which AC plug is correct for a 1960 FI and responses have been both AC 46 and a reference to Nolan's book which states on page 316 that they were AC 44Fs. Anyone know which is correct or are they both correct?

[Joe L.]

Re: Correct C1 FI spark plug?

I've looked at archived postings regarding which AC plug is correct for a 1960 FI and responses have been both AC 46 and a reference to Nolan's book which states on page 316 that they were AC 44Fs. Anyone know which is correct or are they both correct?

Keith----

GM says it was AC 46, although some other sources say it was an AC 44. It was not an AC 44F, though.

[Ray C.]

Re: Correct C1 FI spark plug?

I believe there was an increase in heat range for the high performance engines due to plug fouling. GM issued a change from the AC 44 to the AC 46 plugs. I am not sure of the date this change was issued.

I now use AC-R45-S plugs in my 270-HP and will use the same plug in the 315-HP 1961 currently under restoration. I believe the AC-46 are no longer available.

Ray

[John H.]

Re: Correct C1 FI spark plug?

AC 46's replaced AC 44's for all Corvette engines in production on May 9, 1957, S/N E57S103268, per TSB #DR-295, issued May 22, 1957.

AC 45, R45, or R45S will work fine; the AC 46 was discontinued three years ago.

[John D.]

Re: Correct C1 FI spark plug?

I've looked at archived postings regarding which AC plug is correct for a 1960 FI and responses have been both AC 46 and a reference to Nolan's book which states on page 316 that they were AC 44Fs. Anyone know which is correct or are they both correct?

Keith, If you have an original 107 coil and some good spark plug wires,etc and drive the car down the interstates the AC 44 is fine. But since most of us don't I would use AC 45 or AC 46. Be careful though using the 45S or 46S plugs as they may hit the pistons. S means extended tip.
These are flea market plugs and the prices are going thru the roof. Try ebay as once in a while you can snag some at an affortable price.
Fuel cars work well with the hotter plugs. If you foul out a set of those you most likely have some serious engine problems. But if you blow a cranking signal valve that usually trashes the plugs. John D.

[Roy B.]

Re: Correct C1 FI spark plug?