no remember o ring uses a stock gasket with a ring
fire ring uses a modified gasked where the factory ring is removed and only a wire is used
but both can be cut in the head its apparently determined by the gasket type and the size of the ring. atleast thats me putting together both sides of this to make one statment.
and oh ya rpms play a big factor too. its just kind of amazing to me how different they are but at the same time how similar gas and diesel engines performance can be applied. something to think about too, some of the sled pullers will turn 6k to 7k going down the track granted they are p-pumps but quadzilla has a program for the adrinaline out now you can get the vps to turn to right at 4500. mine has this on it and its pretty impressive. they will hit the fuel cuts like an import will. it doesnt stop fueling till the rev limit set is hit.