These plugs are ideal for Z20's above about 250hp upto about 500hp. You want an 8 past that really, or even say 450hp+ if it's pure track abuse rather than a road car.
Colder than the standard 6's that Vauxhall fitted, these are suited to higher horsepower, and are for people that use their engines hard.
We tend to gap them to around about .7mm for most builds.
This is for a pack of four, delivered to your door.