Spark plugs heat ranges

Hi all,

What do spark plug heat ranges actually do? Basically my local halfrauds only has RC7 YCC plugs in and would they be any good?

Would that one heat range make a difference?

Thanks for putting up with all my silly questions

Anyone going to Brands this Sunday? Or Bedofrd on the 14th Feb?

A question for Roxy here, he will be only too happy to answer, as he investigated a lot on it some months ago…

Cool, I read all the stuff about the RC6 YCC jobbies, just wondering if &'s would really make a major difference and what spark plug heat ranges actually mean…

For Champion plugs the lower number means the plug runs cooler - which means its less likely to overheat and cause running on - pre detination etc - it is however more likely to get fouled up.

Foe NGK the numbers go the other way


Go to for all teh infor you never wanted.

PS - Dont use the 7’s IMHO - get the 6’s and dont be tempted by the fancy thin electrode Platinum plugs - they dont work in the VHPD - again IMHO

Nah after what was said I was just gonna get cheap plugs and change them often…

So the heat range of 7 is more likely to cause pre-detonation? That’s bad!

I’ll hunt around for some 6’s or the NGK BKR7E’s…


DO NOT USE CHAMPION heat range 7 in your exige !! It might be okay pottering around but at the track it will prolly lead to detonation… that is very bad !!

The heat range is very important… you already read the other posts on this so we won’t go over all that but I would advise sticking to Champion RC6 YCC - however, I do believe the NGK BKR7E is a correct equivalent.

The other thing to be careful of is that you need a flat seat with a washer… Don’t use tapered seat plugs or u risk damage to the cylinder head… like the detonation… that would be very bad !!


Too hot a plug leads to detonation leads to holes in places there ai’t supposed to be holes (like pistons !!)

Too cold a plug leads to fouling which will lead to misfires but isn’t as bad as detonation…

you can see both conditions by looking at the plugs (don’t let the car idle long before switching off to remove the plug… the NGK site (Andy pointed to) explains all this.

Get the Champion RC6 YCC here really top spark plug guy �2.85 each, they’ll arrive next day or the day after… tell Rob & Rebecca that sent you… sorry Mr Admin if this is too close to a commercial

Cool cheers Rox!

Makes sense now, and just ordered some from Just get 'em gapped and I’ll be off! Yay!

Also should have the definitive answer to my misfires on Friday so it’s all gravy baby!