GT40/GT40P Head questions

Waz900 · Apr 6, 2007

I'm interested in picking up a set of GT40 or GT40P heads for my 92 LX. I have a few questions to ask before I make my decision

1. Which are better? GT40 or GT40P. I was under the impression that the GT40P breathe a little better but I have also heard that the original GT40 heads are better, b ut I do not know why.

2. If I get them off of a 302 explorer, can I just bolt them on and be done, with no problems? Or are there some kind of adjustments that I have to make before I can put them on my car. Are there any hookups that are on one car that aren't on the other? Or are there certain connections that need to be added?

3. Right now I have BBK shortie headers on my car. Is anyone running these headers with GT40 heads? I am concerned as to if there is going to be a problem with the spark plug set up on the car.

4. If I were to get a set, and have new valves and springs put on them, anyone have a ballpark as to what it would cost?

Thanks in Advance!

85_SS_302_Coupe · Apr 6, 2007

P heads will flow a tad better than non P heads, but they also have a larger combustion chamber so you'll get a little boost in compression with the non P heads. The hot trick around here is to get the P heads milled down a little so they bump compression up. You'll need P specific headers if you run those, as they have a funky spark plug angle and with most typical headers they'll hit the pipes, although you can use MAC full lengths and a few other full length headers. I'm not too sure about what EFI stuff needs to be dealt with or what the cost would be for valves and springs.

Around here it's not uncommon to see guys with stock Explorer engines (with P heads), a cam and slicks/gears running high 12s all day long.

Waz900 · Apr 6, 2007

So if I use the regular GT40 heads, will I be able to use my BBK headers or do I still have to change them?

85_SS_302_Coupe · Apr 6, 2007

javier302 · Apr 6, 2007

gt40 u can still use them...

U2SLO450 · Apr 6, 2007

tri state cylinder head is where i got my gt40p heads from. They already have the 1.94/1.54 valves in them and stronger springs and you can get both heads complete for under 600$

Cwalk · Apr 6, 2007

U2SLO450 said:
tri state cylinder head is where i got my gt40p heads from. They already have the 1.94/1.54 valves in them and stronger springs and you can get both heads complete for under 600$

How did they work out for you? How much power and 1/4 ET's?

notsoslo5.0 · Apr 7, 2007

yeah im also very interested in power and tiems, and when i do decide to get heads, i was planning on going with bbk longtubes, would htis work? another thing, if i were to get these heads complete like you what kind of cam would i get and what else would i need to get?

Waz900 · Apr 7, 2007

I'm probably going to go with the E303 cam. I hear its one of the best for street applications. It's supposedly good for mostly stock setups and it doesn't have too much lift.

Mike92GT · Apr 7, 2007

Where are you located? I have a used set of cast iron GT-40's that I'm selling cheap, they just need a little work. I don't really want to ship them though 'cause the're so heavy

jtfairlane · Apr 7, 2007

85_SS_302_Coupe said:
P heads will flow a tad better than non P heads, but they also have a larger combustion chamber so you'll get a little boost in compression with the non P heads. The hot trick around here is to get the P heads milled down a little so they bump compression up.

You've got it a bit backwards. The standard GT-40 heads have a combustion chamber that is approximately 65cc in size. The GT-40P combustion chambers are around 60cc. Because the GT-40P heads have the smaller combustion chamber, they will slightly increase compression on a stock 5.0 motor as is, without milling. You would lose a little compression with the non-P GT-40 heads.

U2SLO450 · Apr 7, 2007

Cwalk said:
How did they work out for you? How much power and 1/4 ET's?

I dont even know yet, all the parts are sitting brand new in my bedroom:banana.I also have a new cobra intake, e-cam, and i just installed the frpp "p" headers and off road h pipe, and flows

85_SS_302_Coupe · Apr 7, 2007

jtfairlane said:
You've got it a bit backwards. The standard GT-40 heads have a combustion chamber that is approximately 65cc in size. The GT-40P combustion chambers are around 60cc. Because the GT-40P heads have the smaller combustion chamber, they will slightly increase compression on a stock 5.0 motor as is, without milling. You would lose a little compression with the non-P GT-40 heads.

Are you sure? I could swear the older heads had the smaller chambers...i seemed to remember that being why everyone milled the P heads. I could be wrong though, i've never measured either.

KurtPB · Apr 7, 2007

so what kind of power can someone expect out of a 302 w/ GT40p's, e-cam, decent headers(i dont know much about these) and a good exhaust?

jtfairlane · Apr 7, 2007

85_SS_302_Coupe said:
Are you sure? I could swear the older heads had the smaller chambers...i seemed to remember that being why everyone milled the P heads. I could be wrong though, i've never measured either.

I'm not claiming that people don't mill the P heads, but yes, I am quite sure that the standard, mexican cast, GT-40 heads that came on the 1993 Cobra and early Lightnings had significantly bigger chambers than the 60cc GT-40P. Bolting on a set of bone stock gt-40P heads onto a 5.0 that had E7TE castings will produce a slight compression increase.

Waz900 · Apr 9, 2007

So if I get a set of GT40(or GT40P) heads from a lightning or an explorer, can I just bolt that on and run it? Or do I have to change the springs or anything on it?

jtfairlane · Apr 9, 2007

Waz900 said:
So if I get a set of GT40(or GT40P) heads from a lightning or an explorer, can I just bolt that on and run it? Or do I have to change the springs or anything on it?

That depends on your camshaft profile and the condition of the valves/springs/seals on the used heads.

Waz900 · Apr 9, 2007

Assuming that the springs on it are in working order with an E303?

KcMstang · Apr 9, 2007

I just did this swap last weekend. Picked up GT-40p heads (already machined) for $300 w/ e303 ($40) and Cobra upper/lower (freebie). I saw my headers weren't going to work so I drove to Summit and picked up the Ford Motorsports headers made specifically for the 'p' heads. Now I'm having a fuel pump issue so I can't drive the car to see how it feels. When I rev the motor my fuel pressure drops to about 23-25 psi.

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