gt40's are OEM cobra heads P's did NOT come on cobra's but came on explorers / mountaineers
the P are pretty identical beside having the "revised" spark plug angle which give it a better burn and a little bit more power. thats why they also require special headers to clear spark plugs.
Gt-40 heads did come on 96 exporers for a while. They are slightly different than the 93 cobra versions and have no thermactor passageways inside them...but neither do the p heads.
P heads use the same size intake valve of the gt40, but the smaller exhaust valve of the e7 head...as well as a revised spark plug angle. They also require special headers or angled spark plug boots.
P heads can be had cheap....$200 will get you a set off the truck.....cheaper if you go to the junkyard and get it yourself. Grab the intake an throttle body too....both can be used and the intake is similar to the cobra gt40 intake and 65mm tb.
yesterday is history tomorrow is a mystery
