how would it lag when all your waiting for is rpm and not rpm+spinning the turbine? the rate at which the rpm increases may not be instant but rpm increase is a lot faster than turbo lag. as for the size it is a t3/t4 .48hot .60cold 57 trim. it is the same size that others have used and isn't too big for street use. I really can't get too much smaller on the hot side and any smaller on the cold side and I won't get 20psi