spark plug question

[rick spears]

i recently purchased a 70 coupe 350/350hp car. i am doing a tune up and realized that the spark plugs reccomended for the engine are no longer available...(AC R44)
my question is this, which plug would be a good substitute for this? R43? R45? or something else. i will primarily be driving it around town. and the engine is totally stock, never rebuilt. thanks! rick

[Dick W.]

Re: spark plug question

R-45 would be the best choice. R-43's would have a tendancy to foul while driving around town.

[Duke W.]

R45 is perfect!

The original heat range "4" is actually a bit cold for normal road use. AC heat range "5" or equivalent is just right for ALL small blocks, regardless of power rating.

The first "4" stands for 14 mm thread. The second digit is the heat range, and in the AC heat range numbering system a higher number is a "hotter" plug. A hotter plug will run at a higher operating temperature and help burn off deposits, but not overheat in any normal street use.

AC heat range "4" is okay if all you do is high speed highway driving. AC heat range "3" is just right for hot lapping race tracks.

Duke

[rick spears]

Re: R45 is perfect!

thank you guys, i appreciate your input. i was "leaning" towards the R45, but now can proceed with confidence!!! i have been running R43S in it for a couple of months, but didn't like the results.....thanks again, rick

[R N.]

Re: R45 is perfect!

Hi Duke,

What about the '70 LS-5, what would yourecomend here?

Thanks,
Kurt

[R N.]

Re: R45 is perfect!

Hi Duke,

What about the '70 LS-5, what would you recomend here?

Thanks,
Kurt

[Joe L.]

Re: R45 is perfect!

Rick-----

I think that the R45S ought to work as well or better for your application compared to the R45. If you don't like the R45S then I don't think you're going to like the R45, either. My advice: use Champion RJ8C.

[Joe L.]

Re: R45 is perfect!

Kurt----

I can't tell you what Duke recommends; he'll have to speak for himself. However, what Joe recommends is Champion RV17YC.

[Duke W.]

Re: R45 is perfect!

Probably also AC heat range 5 in the proper geometry for a big block. If you want to run AC plugs (for judging) AC crosses Joe's recommendation to the R46TS

I prefer NGK and Denso plugs, and they make non-resistor equivalents to the discontinued AC45, which was just right for pre-'69 SBs.

Duke

[george romano]

Re: R45 is perfect!

You want an Autolite 86 in that 350 horse car.

George

[rick spears]

Re: R45 is perfect!

joe, i think you misread my response, i said i didn't like the way R43S performed in my car. i'm gonna try the hotter R45 plug this evening and see how it runs....thanks for your response though! rick

[Duke W.]

Re: R45 is perfect!

What AC heat range is the Autolite 86 equivalent to?

Duke

[george romano]

Re: R45 is perfect!

Not positive Duke, but I remember it being equivelent to the R45. I owned my 69 L46 24 years ago!
The Autolite's seemed to last forever in that car, and I've used them in every car I've owned since, even my Mopar.

George