The heads on our motor flow well over 500cfm. Every time we found flow on the intake we got a good result. We have also spent a lot of money and time on the exhaust side with almost no gain. There is very little hp to be found on the exhaust and with headers. I don't think there is 15 hp between the best set of headers out there and the worst set. I would trade valve size from exhaust to intake anytime.