I just recently purchased a 88 gt and have to do some motor work to get it street worthy. I'm new to the mustang scene, but always wanted one. so my question is, what cars can i get the gt40 heads off of and are there any supporting mods to do the gt40 set up. Thanks!
Both heads are similar as far as performance. The P heads are generally considered to flow better, but i read in one of the mags that Robin Lawrence swears by non P heads and says those flow the best. The P's will give you a tiny bit more compression due to smaller combustion chambers. The down side to the P's is that they have a revised spark plug location, which turns the plug and points it towards the center of the chamber, which changes the angle that the plug screws into the head, which means you have header clearance issues. There are P specific headers, as well as *some* headers which will work (typically, Mac full length headers are pretty well known to work with P heads). Both use the same style rockers. GT40s can be had from 5.0 Cobras and Explorer/Mountaineers up to mid '97 when they switched to the P version. The easiest way to identify them is to look at the front end of the head, you'll see either III or IIII cast into the head, with III being GT40s and IIII being the P's.