An old question but been that long I've forgotten

What's best plugs to run with a fairly modded zed running around 600 hp

Iridiums or copper core and how cold what grade

Rich

I would say at least 7's, iridium for longer life but coppers for performance.. (coppers will end up costing more over the long run as they wear out a lot faster)

what heat number is the stock plug ?

most people use 6 but I think it's 5 as well (it's in the FSM & the owners handbook) :)

You need Iridium NGK BKR8EIX which are Heat Range 8 :thumbup1:.

so you want a higher mumber so can a 8 range plug handle more heat in cars with more power is that rite ?

I run BCR8ES in everything from my Zed running 450bhp to my 2L MR2 running 490bhp (2.3 bar). MGT run BCR8ES in their 8sec RA28 Celica. Either copper BCR8ES or Iridium BKR8EIX, they only have one job to do and that is to provide a spark. Both do that very well in a 600bhp Zed, and it's unlikely you'll be doing 20k miles a year (I'm assuming), so either will be fine :)