Thank you, Eric, that was EXACTLY what I needed to know. I know of an explorer at my local U-pull it which would be a prime candidate. I was not aware that the only explorer heads were the P models. This means i will need to get new headers, which is unfortunate because I bought brand new Shorties for when I was going to stick with the E7's. I saw a set of GT40 heads on Craigslist a while ago for cheap, but someone snatched them up and now the only ones are $300-$350. what do you suggest? sell the headers and get the JY heads or keep the new headers and pay the extra for the GT40s on CL? I hear performance wise the P's are only minutely better.
You're welcome, sir.
I apologize, in advance, for the long-winded response to follow...
Well, the very early 5.0 Explorers ('96-early '97) are said to have had the remainder of the GT40 heads, that were left over in Ford's inventory, used on them. I, personally, have never found one of these in the JY's that I frequent. All I've ever seen on the Explorers are the P heads. Many people do say this is true, though.
The GT40P heads are, slightly, better performance-wise. They are, pretty much, the epitome of, production vehicle, cast iron cylinder head design for the pushrod 5.0. However, between the two, at the performance level you're building to, you might see a ~5-8 hp difference. Maybe. When you start using a higher-lift cam, more duration, with less LSA (i.e.- .500+ lift/110* LSA) is when you are utilizing more of the head's flow potential. This is when the differences become more apparent.
Personally, I chose the GT40 (Cobra/Lightning) heads because I need to keep my emissions stuff. Also, I'm using shorty headers off a first-gen Lightning. Direct bolt-on, factory part, inexpensive, and designed
to work in our F-series chassis. Picked them up off a Lightning forum for ~$100.
My opinion: JY GT40P's and new headers ~$300 (plus any machine work/rebuilding on the heads), minus the price offset from selling your current headers. CL GT40's ~$300 (plus machining), minus the offset of negotiating the price down (maybe).
It looks like it would wash-out, about, the same either way +/- $50. Therefore, the decision should be based on peripheral factors: Do you need your emissions equipment? How well will the P headers work in your engine bay? Are you going to want well-flowing heads to "grow into", performance-wise, at a later time?
Finally, IMHO, I don't like the idea of, possible, "hiccups" with parts that are not designed to work well in the, over-all, vehicle application for my DD. I don't like saying, "Well... I had to tweak that to make it work." or "Yeah... that doesn't fit quite right, so, it makes things hard to access and work on." When you pop my hood, everything looks and functions like it belongs there. I'm a big fan of, brutal, simplicity and ease-of-maintenance on my DD's. I can play Hot Rod builder with my street car.
Just my $0.02,