467-Ratman

I am currently running a champion RV15YC4 plug in my rat, they are according to the guys at CarQuest not a very hot plug, should I be using something different? My motor runs a little rich at idle and the plugs are usually pretty black except for the strap which is dark brown. Are platinum plugs any better.... They were telling me about the AC Delco platinum #1 plug being a good plug?

1972 Shark

I don't have a BB but I'm running a set of AC Rapid Fire # 10's in my SB and have had no problems with fouling.

zwede

Whoever you talked to at carquest is wrong. That's a very hot plug. The code breaks down as:

RV15YC4:

R=Resistor
V=14mm thread, 0.460" reach, taper seat, 5/8" hex.
15=Heat range. Higher is hotter
Y=Standard projected tip
C=Copper
4=Wide gap (I think ~0.044")

I'm also running champion plugs in my 454 and I'm at heatrange 12 (colder than yours).

I'd say fix the carb. :)

You can also try to switch to NGK. They have more of a projection of the tip which tends to resist fouling better. The equivalent plug for you is UR4 for standard gap (0.035") or UR45 for wide-gap (0.059").

467-Ratman

Any problem with using a hotter plug? The car seems to run well with no misses. He also told me the AC delco rapid fire #1 was the same heat range as the champion, wrong on that one too?

norvalwilhelm

I like ACCEL # 276 normal heat range and #274 a colder plug in the front corners. I have had these sample plugs in my engine for 3 years and they still look like new.
They also make a S plug which is shorter then normal for header clearance. You should not cover up a rich problem by going to hotter plugs. The cylinder walls are getting washed down and the rings will not last.
Fix the rich problem.

zwede

Thing is, you will be hard pressed to find a hotter plug. The ones you have are pretty much as hot as they get.

Not sure if they would cross to a RF #1... Last time I checked the RF #1 crossed to a NGK FR45 with is gasket seat, 3/4" reach. Yours are taper seat 0.460" reach. The RF #1 is the same heat range though.

467-Ratman

Actually my question should have been is it ok to use the plug I have now? I dont want to go any hotter. I ran the rapid fire plugs for about a month before I went to the dyno, the guy told me they were too cold of a plug, thats why we changed. They still look very good though, not fouled up or anything. They were expensive too! Another dumb question, what makes a plug hotter or colder, is it the reach?

zwede

If the car runs well the plugs should be ok. Just keep an eye on them.

The heatrange is determined by the design of the center electrode porcelin portion of the plug. If you look at the cylinder side of the plug you can see that the porcelin extends into the shell until a point where it mounts to the shell. The length of the porcelin before it contacts the shell determines the heatrange. If the porcelin is short, heat is conducted easily to the shell, and then to the cylinder head and that is a cold plug. If the point where the shell and porcelin meet is further out (towards the plug wire end), heat is not as easily conducted to the shell and that is a hot plug.

467-Ratman

Thanks for the info! I think the RF#1 looks about the same for the length, but you said the reach is longer? 3/4, If so would that be a colder plug or hotter than the champion?

467-Ratman

The other interesting thing at the dyno shop was when he changed from the RF plugs to the Champion we made another run and the difference was 20HP more! Pretty cheep hp gain for just changing plugs....