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Message: <blockquote data-quote="DropTopPony" data-source="post: 107772" data-attributes="member: 7995">Its the info that was spread around in the beginning but has been proved wrong by those who have no financial gain in you buying new heads. I was under the impression that NPI's were junk myself because this is what a few idiots in magazines said so we all believed. But a few guys over on Modular Depot played around proved the bottleneck was the intake/cams not so much the heads. The stock PI heads have larger valves and are capable of higher lift so when the NPI are outfitted with equal size valves and offset retainers they stack up quite well. The big downfall of PI vs NPI heads stock vs stock is the exhaust port flow but Jim at Renegade can fix that up nicely. Go over to TCCOA forums (tbird-cougar) they laugh at us Mustang owners because we are so quick to ditch the stock heads in favor of PI and they can buy them (our NPI's) super cheap and send them off to Renegade.</blockquote>