Will stock tubular exhaust manifolds work with GT40Ps? I've heard yes and no. I don't have the bucks for headers yet and would like to get by with the stockers for now. Thanks.
They should but you may have to run a short plug in the rear-most cylinders and be careful with your plug wires. I know that the standard MAC shorts will work this way so I will guess that the stock header will be similar.
No. The plugs, reguardless of size are going to hit the primaries. The problem is that the plugs are in a different angle than typical Ford heads, and come almost straight out of the side of the head, and straight into the header pipes. The "P" headers come straighter/further off the heads to clear the plugs. MAC shorties will not clear, but MAC full lengths will because they come out far enough to clear them.
Anyone saying they're using short plugs or certain headers, are either extremely lucky or are running regular GT40s, and not the P's.
Ok, if that's the case, where can I get shorty headers that work with GT40Ps? My usual sources (Jegs, summit, etc.) make no mention of P specific headers.
See if MAC will sell you the P specific headers or Central Coast Mustang.
I bought two pallets of GT40P heads and I had some brand new MAC short headers. I bolted the headers to the heads and I did have regular length spark plugs installed. The rear-most plug did make a tad bit of contact with the header, or there was so slight clearance I knew the wire would never go on - don't recall exactly. Either way, I then installed a short plug back there and had room for the plug wire.
If you don't want to take a chance, get the P headers but if you know someone that has some standard MAC shorts lying around, try them and see.
I have BBK shorty headers and and regular plugs for the explorers.
You can search for my thread titled "pics of gt40P shorties and BBK headers" or something like that. To change plugs, I had to remove the drivers side header, (PITA), and a motorcraft plug wire turned backwards (you'll see it in the pics), but they work!