a few years back somebody on this website flow tested a stock intake and IIRC they got 200cfm. think about it. a stock head, which is inadequate for performance, will flow a little better than 200cfm. I don't think intake manifolds by themselves dictate peak rpm, but they will dictate a power range. I think valve train stability is more of the key to peak rpm. take what the marketeer's say with a grain of salt.