ive been using the NGK UR45 spark plug, which is their highest heat range, on a fresh build and I have slight detonation. I was looking at possibly an accel 276s. is that a step down in heat range? ive been trying to find a chart and cant find one please help.

 

Always best to start at the "middle of the heat range" if you've modified the motor at all and see what it likes from there (boosted/nitrous applications you start dead-cold and work your way up). And especially important to get the right STYLE of plug for the heads. If you're screwing an old set of .460" reach taper-seat plugs into a set of aftermarket aluminum heads that take a .750" reach with a gasket seat.... it won't work very well. Check with the head manufacturer and see what plugs they recommend for it as a starting point.

 

the NGK UR45 was the recommended plug for those heads. it was very slight detonation, which is why I was thinking just a step down would be ok.

 

I've never had good luck with NGK heads on old Chevy motors. Acel or AC Delco all the way.

Have you tried or thought about backing off your timing slightly?

 

well accel is what im going for which is why im looking for a heat range chart. im looking at the 276s but im not sure what the ranges go to for accel. those are heat range 6. I tried adjusting the timing but im still having an issue.

 

NGK UR45 crosses over to an Accel 0586.

One step colder will be an Accel 0574.

You can go to Accel's web site and download their catalog. All their spark plug information is there.

 

Only one way to find out; and it isn't posting on the Internet.

It involves a parts counter.