Prostcelica, I went to Edelbrock website and read the info on the E street heads. Flow rate isn't much different than the performer rpm head. The listed valve spring diameter is 1.25" and the performer rpm valve spring diameter is 1.46. Max lift is .550, max lift on performer rpm is .575. Under technical notes it says use with hydraulic flat tappet camshafts .550" lift. Not compatible with hydraulic roller camshafts.