i have a microtech lt8, garrett t04s, isuzu npr large intercooler, so on and so forth. i am going for 400 rwhp, my question is what heat range plugs tyo go wiht? will 10s be fine or do i need to go with 11.5? also where is a good place to get them form?

 

My own personal experience tells me you'd be OK with 10's all round, though they'll foul in next to no time if you aren't revving the guts out of it everytime you drive it. Gets expensive.
Motorbike Specialists seem to be the cheapest place to purchase the NGK B9EGV's that are commonly used in rotors here in Oz (avg AU$13)
Though if you buy a box of 12 plugs, and have a SOMEone/ANYone you know who can get Trade Price on them they come down to about AU$8 per plug.

 

is it the colder the plug the shorter the life?

 

Colder plugs last longer, but foul faster. And they reduce that nasty thing called preignition or detonation...

 

Street driving, stick with all 9's.
When racing, you can go with the 10.5's and 11's.&nbsp You really can't run the colder spark plugs on the street, as they will foul with city driving and cause the engine to run poorly or not at all!



-Ted