Which race spark plugs and where from?
 

I have BUR9EQP spark plugs on my car which are ok for the break-in period but want to upgrade to better plugs for after the break-in period.

From what I've read 7420s are the way to go and Greddy versions are cheaper. I can't find it in any of the forum vendors' websites. Where can I find these?

But more importantly, I have a GTX35R and meth/water injection (my goal is 400-450whp). Planning to run 15psi daily and go up to 18-20psi for racing. The plugs I buy should NOT require a special socket, SHOULD be suitable for both slow daily driving and racing (low and high boost) and not foul all the time.

Which heat range should I order my 7420s in; 10, 10.5 or 11??? :scratch:

PS. My ignition system is almost stock except the HKS Twin Power.

The GReddy plugs are no longer available.

We have the NGK 6725 and 7420s available. $33.50 each.

Which heat range plugs would be the best for my application; 10, 10.5 or 11?

10 or 10.5 will work fine. Err on the cold side. Just need to make sure your tune is good so that you don't have fouling issues. I've run 11s on similar setups to what you have with no issues. That cold of a plug is not needed, but, with a good clean tune, it is possible.