tru-blue 442

I'm sure this subject has been beat to death.
Need to settle a bet. Involves the risitor plugs,
r-44,r-45,r-46 and r-47. All are S plugs too.
They are hotter as you go up, correct?
I can tell no difference in the lenght of the plugs,
or the lenght of the insulator tips either. They
really do look the same.
Also, if I am correct, would you guys think
that the r-47's would be a good match
for the pertronics electrical kit I am going
to be installing in place of my points set up?
Application is a 68 F block with C heads and
original dist. from a 70 442.
I was thinking about using an acell coil,
but for now I have the original gm coil.
Any thoughts? And thanks again guys, Adam.

rocketraider

47's are too hot. I can about promise you'll get into detonation problems with them, especially with an aggressively curved distributor. A 45 or 46 is going to be your best bet in AC- generally the coldest plug you can run without fouling is the best application for that engine.

All the S suffix means is an extended tip plug. Puts the electrodes deeper into the cylinder and closer to the piston, which you need to watch if you're running flat-top or domed pistons. They became popular in early years of smog control to get more fire into the cylinder.

If you use the Accel coil, open the gaps up to about .040, maybe as much as .045 to take advantage of the more powerful spark. Play around with gap and see what the engine likes best- you may find out it likes .035.

MDchanic

I believe AC plug numbers go up with the heat range, so R44 should be the coldest and R47 should be the hottest.

I can't say anything definite about what heat range you need - I always try to go with the factory recommendations, and with how the plugs look. It will partly depend on how you're driving it - you'll want cooler plugs for highway or high-performance driving, warmer for low revs and idling (like parades).

- Eric

edit: looks like Rocket beat me to it!

jag1886

Yes the heat range goes up with the #. Don't put a hotter plug in with the Pertronics, just use what the car is suppose to have. The heat range is determined by how long the tip of the plug is to where it contacts the metal body, it's almost impossible to see unless you cut the sparkplug open.

tru-blue 442

Original application shows a 44-S.
Of course the R-44S is what I have
been using for years on all my 455's.
Those seem to be getting harder to find though.
They have been out of production for a while now.
I have had real good luck with those
and have also used the R45S with about
the same performance.
If anyone can use some R-47 S plugs,
I have about 6 boxes of them. If they
are to hot, I won't even try them. I can't
think of much worse than a few holes in
a few pistons!

Bunser

I'd go with the 45s and see what they look like after you put some miles on them. Don't underestimate AC Delco coils which could very well be better than Accel, actually, they ARE better.