NGK spark plug heat range question
 

Ok guys I'm getting ready to order plugs for my engines. I'm thinking about ordering r5671A-8 NGK's. Here are the engine spec's
502 - AFR 315's, 8.75 to 1, Naturaly Aspirated, Holley HP 1000 carbs, DUI ignition (HEI).

Do you think the "8" heat range is a good starting point for me, or should I go hotter/colder?

Thanks,
Frank

Frank,

I would start with the 6 heat range and go from there. From personal experience I would rather go too cold than too hot.

the lower the number the hotter the plug on ngk's but 6 is agood start....

Sorry for the confusing post, baja is correct on NGk. I think their heat range runs 2-12 with the lower the number being a hotter plug, which is opposite of AC Delco.

An 8 is pretty much what i run in almost all of my N/a motors... Everything from 2 stroke dirt bikes to hot rod big blocks. We run 9's in some of the race aplications but they will tend to load up more if ideling much. Just my .02.


Darrell.

Guys the best way to find the correct plugs heat range is by reading what the engine asking for for example if the plugs that are in the engine now have the lower three threads discolored from heat this would be the correct heat range plug if the plug only had two threads of discolored you would go with the next hotter plug if you had four threads worth of heat you go colder this is the way I tune for optimumheat range and it is possible to have two engines side by side in a boat with two different heat range plugs. So if you want to get it right after you change the plugs make a couple of passes and use this as a rule if you're too hot or too cold you know how to fix it . This is the same for every engine two stroke or four I hope this helps you it's taken me along time to figure it out and I use this method from my sons race karts which are two stroke to my 1200hp race and poker run engines. Best of luck as always SIncerely Laz Mesa
P.S. CHeck us out at www.mesaracingengines.com

I agree with the NGK 8's for low compression, NA general use. We only used 9's for racing.

Interesting. I was running r43xls last yr NA. Per Laz's method it looks like 2 turns of color on those plugs, so a tad cool. This yr I am running 4lb boost so I wanted to go 2 sizes cooler than the 43s to 41s. Those I could not find, so I went to the NGK site and crossed it to an NGK plug. I found the equivilant plug to be a BPR5EA - L - 11 per their site. It seems that 8s would be too cool, but I don't know. Take it for what it is worth LS!.

Frank,

I have basically the same motors with a similar set-up and I have tried both the "9's" and "8's". I have found the 8's run cleaner and the read is good.

Dave

Frank,

I also have a few sets of 8's here...Do you need a set?

PM me!

Dave