C2 spark plugs

[William F.]

Been covered in general before, but not sure if this specific point was covered. Do NGK, Denso, or Autolite make NONresistor spark plugs with extended tip and 44 and 45 (in AC rating) heat range, correct thread for mid year SB's, or are they all resistor now?
Thanks

[Wayne M.]

Re: C2 spark plugs

The Denso-to-AC cross tables show that AC44S (IIRC, the S means extended tip) is Denso W16PR-U, and the AC45S is Denso W14PR-U. Unfortunately, they list their same two part #s for R44S and R45S, so my deduction would be that they're resistor.

(link): http://www.denso.co.jp/ja/products/a...f/1002_01.html

[Gene M.]

Re: C2 spark plugs

What is the plus and minus to resistor or non resistor plugs?

Are not the extended tip a question mark with dome pistons as in the 350 and 365 horse?

[Duke W.]

Re: C2 spark plugs

The first digit in the AC numbering system - 4 - stands for 14mm thread. The second digit is the heat range.

Resistor plugs reduce RFI emissions, but they "steal" some energy, and the single point system doesn't have a lot of reserve to begin with.

Most resistor plugs that use a descriptive alpha-numeric part number system have an "R" somewhere in the designation. Autolite does not use a descriptive numbering system.

The Denso W14-U and NGK B4 are equivalent to the out-of-production AC 45, and all are non-resistor type. Note that none of these plugs have an "R" anywhere in the designation.

The Denso equivalent to the non-resistor extended tip AC 45S is the W14P-U. NGK does not offer an equivalent.
In the AC heat range system a higher number is a hotter plug. NGK and Denso are the opposite. A lower number is a hotter plug.

AC heat range 5 ~ Denso 14 ~ NGK 4

AC heat range 5 or equivalent in another brand is best for normal street and highway driving, drag racing, and autocross for most vintage Corvette engines. Road racers and track day hot lappers should go two heat ranges colder for OE engine configurations and three ranges colder if the engine is massaged for greater power and revs.

Duke