Someone posted a heat range chart for the NGK plugs and the part numbers a while back. I have searched but can not find it now. I want to go at least one step colder than the TR6. Can't find it on NGK's site either. Can anyone help.

 

From what ive read on the NGK's the higher the number the colder the plug is....and lower the hotter.....

 

TR7 would be the next colder plug in line.

 

+1 on the TR7

 

Theres not an actuall plug called a "tr7". The next colder plug than a tr6 would be part number R5671A-7 stock number 4091 which has a compression gasket seal on it, but will work fine with your heads. This is a cold plug and will kill you n/a. I dropped .2 tenths of et running n/a with this plug

 

Talked with a tech guy at NGK. He suggested I try a BR7EF, stock #3346. Said it was 1 range colder than the TR6 with full ground strap but recessed porcelain. I'm going to try these with 2* less timing and little more fuel.