Will GT40 Ps work with MAC 1 5/8" shorty headers? PLEASE HELP!

astronut1885

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#1

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I have a line on a set of GT40P heads for my car for 200.00. These are not the ones previously posted about that were in a fire. These are in great shape and 100% guaranteed. What I need to know is whether or not these heads will work with my headers. I have MAC 1 5/8" HTS coated shorty headers. These do not have the metal piece joining all the collectors, they are individual. I want to put these heads on when I do my explorer intake in a few weeks, but I don't want to buy the FMS headers if I can avoid it. The problem I am referring to is the spark plug access/plug boot melting issues. If anyone can help me out, I'd appreciate it. Thanks guys!

 

remat457

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#2

• Dec 20, 2003

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astronut1885 said:

I have a line on a set of GT40P heads for my car for 200.00. These are not the ones previously posted about that were in a fire. These are in great shape and 100% guaranteed. What I need to know is whether or not these heads will work with my headers. I have MAC 1 5/8" HTS coated shorty headers. These do not have the metal piece joining all the collectors, they are individual. I want to put these heads on when I do my explorer intake in a few weeks, but I don't want to buy the FMS headers if I can avoid it. The problem I am referring to is the spark plug access/plug boot melting issues. If anyone can help me out, I'd appreciate it. Thanks guys!

Click to expand...

I had always thought you had to have special headers (I think that MAC makes them in addition to FMS) but I read recently that you could get away with 90 degree plug wires???
Anybody know if this is true?

 

matty50racer

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• Dec 20, 2003

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NO! They will not, I had a set of Mac headers on my '87 when I bought it and when I put gt40-p's and FMS headers on I bolted up my mac's just to see if they would work and I saw they definately would not fit on one side.

 

Black331Stang

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NO they will NOT fit

 

astronut1885

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My mechanic said he can reshape my headers a bit to make it work. He knows pretty much all there is to know about modifying stangs, he drives an 11 second 85 LX, and had a 12.3 second 87 GT. He said he can make it happen. Any one know if the headers will work if they are modified? I just don't want to build the whole engine back up and be stuck without exhaust manifolds, and I can't really afford new headers right now, what with doing an Explorer intake and GT40p heads.

 

B

Bigstang1

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#6

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On this subject what exactly is different about the position of the plugs? CAn anyone post a E7 pic and then a gt40p pic for comparison? Anyone know if they will work with flowtech 15/8 shortys?

 

matty50racer

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Bigstang1 said:

On this subject what exactly is different about the position of the plugs? CAn anyone post a E7 pic and then a gt40p pic for comparison? Anyone know if they will work with flowtech 15/8 shortys?

Click to expand...

The plugs stick more strait out from the heads instead of on a steep angle like stock heads.

 

astronut1885

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Can the shape of the headers be changed to work with the Ps? I was told that the only problem would be in changing spark plugs, that you'd have to pull the headers, and possibly you could melt the boots of the wires unless you put heat guards on them. I honestly don't mind having to pull my headers every year or two to do spark plugs, so if that's all it is, then I am not worried. All I want to know is whether or not the headers will bolt up and work with the heads. Thanks again.

 

C.Harris

Da Boss

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I have it under good authority that a shorty type spark plug is available for such a setup. If I recall correctly I believe it was Accel who makes a spark plug with a short porcelain side that allows the needed clearance when using a GT40P head.

I can not confirm this but you might want to check into it.

 

astronut1885

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Any more info on that people? By the way, these are my headers.

 

astronut1885

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Anyone try this and have it work? I am not affraid of modifying my headers or of spark plug access issues, I am more worried about melting my plug wires and whether or not the headers will actually fit on the heads and work.

 

astronut1885

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Also, how much horsepower will I be looking at with my current mods and the to be added mods? See my sig to get an idea of what I have, and I am adding an Explorer intake, the heads, and a MAC prochamber.

 

astronut1885

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I just read that the P heads do not have the provisions for the egr equipment. Is this true, and if so, will it screw up my car? The explorer intake I am putting on with them is setup for the EGR, and I still have full smog, although I currently run a short belt and am putting in a Pro Chamber.

 

Michael Yount

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Apr 10, 2002

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Dec 21, 2003

#14

• Dec 21, 2003

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The P heads came on the Explorers/Mountaineers along with the later style intake with no provisions for internal egr. Do you have emissions to pass there in Somerset? If so, and they do a close visual, you may want to go with the GT40 heads and the early model Explorer intake. They have the air pump and egr provisions that will work with your Mustang components. If you disconnect the egr some people get a check engine light, others don't seem to. If you run without egr and don't turn off the egr function in the computer (chip) some experience part throttle detonation. Others have no problem at all. It doesn't seem to be predictable. You should be able to tell by looking at the P heads whether they have the provisions you're after. The egr port is in the middle of each head on the intake side right between the middle 2 intake ports. The air pump cross-over tube fittings screw into a threaded hole on the back of each head. On the front of the head, the same hole has a threaded reducing insert screwed into it that serves a mounting point for the alt. and a/c bracket.

When I was researching headers for mine Ford Racing told me that the only difference between their new shorties (which ARE P compatible) and their old shorties (which were NOT P compatible) is that the newer header primary tubes extend a bit further away from the heads before turning down and back to the collector. Apparently, that provides the needed clearance for the plugs. However, I'm just referencing what Ford Racing told me by phone. I haven't actually seen a set of P's so I'm not sure how the plugs are actually configured.

 

astronut1885

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Yeah, I knew the P headers were longer necked, but my MACs have pretty good clearance. I just found these wires on summit, and I think they might work, the boots are very small and they are protected up to 600*. Any idea how hot the headers get?

And yes, I do have to pass emissions, but I have a "friend" who doesn't look to close, I pretty much have to pass the gasses test, I've yet open my hood, and once I passed with an OR hpipe on my old GT... I talked to a friend and he said not to worry about the EGR stuff, so I wont.

 

astronut1885

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I just found these too, rated to 1200*F boot protectors.

one other question, if I put these heads on along with an Explorer intake, do I need to do a MAF conversion?

 

astronut1885

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bumping it up so more people will take a look.

 

Michael Yount

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#18

• Dec 22, 2003

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PM tmoss and ask him to come into the thread, or ask him directly your questions about P heads/Explorer intake and speed density. With the stock cam, I don't think you have to go to mass air unless you want to. There are a number of good running speed density combos out there with P heads and GT40-family intakes (Explorer/Cobra/GT40).

 

astronut1885

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thanks again mike. any thoughts on those wires and the boot protectors?

 

Michael Yount

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Dec 22, 2003

#20

• Dec 22, 2003

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My post from the other thread:

"I saw it - the variable is simply how close will your plugs come to your headers; without a test fit I don't know how to tell you if those boots/insulators will work or not. Wish I could be more helpful, but as I mentioned before, I suspect the only way to get complete certainty on this is either to test fit one, or be prepared to do whatever you have to once you've bought 'em. Some folks seem to make it work, the majority go with a P specific header. That info doesn't really help you know whether yours will work or not. Therein lies the problem. Let us know what you decide to do and how it comes out."