Since I've been on FSB , I've seen so many discussion on Ford's GT40 heads I figure I would post a informational thread that should be a sticky.
The GT40 and GT40P heads are one of the highest flowing heads for the SBF 5.0L applications. These are available online, ebay and in some junkyards if your lucky. Aclot of racers that have to meet stock OEM heads requirements, also uses these heads. You can use these on any 289/302/351W engine. All OEM int/exh manifolds will bolt on.
Let's start with the GT40, these heads can be found on Ford Mustang, Explorer and SVT/truck Lighting applications. These heads also boast the larger exhaust valves but don't flow as much as the GT40P that I will speak about later. These heads also flow more than the other E7 E6 heads which can be found thru out most of the ford car/trucks.
These heads can be found on a few Mustangs upto 1995 and on most of the earlier Ford Explorer applications ( approx 96-98ish). They are easily identify by the tell-tale 3 vertical end marks or by looking at the sparkplug at either end and finding the GT stamp.
Also they have a GT stamped on the top of the head and the one machine flat spot at the corner.
Once the cover is off , the oil return galley also has the words GT.
the heads also have the F3ZE AA casting stamped on the bottom side
Most accessories brackets bolts on with no problems. These do NOT have ports for any airpump and reduce emissions. The combustion chamber has the spark plug almost terminating into the chamber, leading to a better burn and reduce emissions. If your looking for a non worry, direct fit head, that low cost and iron. This is the head to buy and use. Ford racing make the same head in Aluminum btw, but at a higher cost. It might be available in some dealer inventory or thru other suppliers.
next the GT40P heads, this is off my girlfriend car. She blew a gasket and we found a crack exh valve, so I loaned my heads out to her. This head is only found on a explorer. The explorer uses the GT40 and up to 98ish they started converting to the Gt40P for even better emissions reduction. A side benefit to this head, it brings the plug out and puts more flame exposed to the incoming air. The only bad thing about this head, it's plug angle is not ideal with stock exhaust manifolds.
Just like the GT40 it has vertical end markings, but 4 lines
It like the Gt40 has the wording GTP and a single P stamped on the outer edge and near the spark plug hole. The flat spot at the corner of valve cover has the P.
The oil return galley has the letters GT40P in that valley. This is only place you will see the full GT40P stamp btw.
The bottom of the head has a different casting number than a GT40
Both heads boast the same size valve for intake but the exhaust is smaller on the P.
GT40 ( 1.54 )
and GT40P ( 1.46 )
Take note of the spark plug hump and the position of where the plug would be between both heads.
Most accessories brackets bolts on with no problems. These do NOT have ports for any airpump and reduce emissions. The combustion chamber has the spark plug exposed into the chamber, leading to a better burn and reduce emissions than the Gt40s.
If your looking for the highest flowing OEM ford heads, this is the head to buy and use. You will have header problems if your choose to use the factory GT40 or regular manifolds. Most people get by with custom headers and with reduce plugs lengths that are found thru accel, with custom plug wires.
More to come