I bought a wide ban O2 system several years back for my car, all the engine dyno shops I use have dual wide bands on thier dyno, annular boosters are famous for going richer the higher you rev the motor, if you have enough fuel supply BTW, there is no way I would buy the 250 or 275 pump knowing I was going to hit it with a 250 NOS shot unless you have a seperate, adequate, fuel system for the NOS. I bought a Magnafuel 500 pump for my next car, that motor will make 900 +HP N\A Magnafuel says there 275 pump are good for 750 HP, the 300 pumps are good up to 900 HP and the 500 pump is bigger and better yet I have all three plus two BG 400 pumps Some lessons are hard learned for some of us