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Dimples
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Discussion Starter #1
Disclaimer: I have no hands on experience on this, just something I heard.

A somewhat reputable source told me that many (most?) SBF headers can be made to fit GT40P heads by adding a header flange and using it like a spacer. You know, the bare flanges used for custom fabbed headers like these:


Too good to be true? Maybe, but I’m interested in trying it out. I’ll report back if/when I do.

Anybody else heard this, or better yet, tried it?
 

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Dimples
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Discussion Starter #3
Makes sense....
That’s the part that got me. I‘ve poked around a P engine on a stand, so I understand the challenge of the different spark plug angle, and I could see this working. Thing is, if this did work, how could it not be common knowledge by now?
 

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Do you put gaskets on either side of the plate?
 

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761443
I'm skeptical. The problem with typical headers is that several of the tubes bend right at the flange backwards. With the typical SBF head the plugs are laid back. The P plugs are more perpendicular getting in the way of the tube itself. The plugs stock out farther as well. The tube really needs to come pretty straight out for about the first inch before turning. A good rule is if you can get a deep socket on the rear bolt of each tube, you have a pretty good shot
 

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might work on an engine stand but spacing the headers out away from the head will cause shock tower clearance problems
 

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Dimples
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Discussion Starter #8
I'm skeptical. The problem with typical headers is that several of the tubes bend right at the flange backwards. With the typical SBF head the plugs are laid back. The P plugs are more perpendicular getting in the way of the tube itself. The plugs stock out farther as well. The tube really needs to come pretty straight out for about the first inch before turning. A good rule is if you can get a deep socket on the rear bolt of each tube, you have a pretty good shot
Yeah I am too, but with the right headers, I can kinda see it working.


might work on an engine stand but spacing the headers out away from the head will cause shock tower clearance problems
Well, I get that it’s tight, but I’m not sure the thickness of a flange would be enough to kill the deal.
 

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Has anyone tried it wit( the repro 2i9 hi PO manifolds or a set of TrI Ys?
 

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I can barely change the spark plugs with the jba gt40p headers designed for my mustang :(
 

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Has anyone tried it wit( the repro 2i9 hi PO manifolds or a set of TrI Ys?
TRI Y will need to be reworked on the drivers side front tubes . part of the reason I ended up with Edelbrock 5.0 heads . I've seen rebuilt TRI Y's made to work though

post 18 has some interesting pics of Explorer exhaust manifolds will gt40p heads fit on a 302
 

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Make a plywood template and experiment with various thicknesses.
 

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View attachment 761443 I'm skeptical. The problem with typical headers is that several of the tubes bend right at the flange backwards. With the typical SBF head the plugs are laid back. The P plugs are more perpendicular getting in the way of the tube itself. The plugs stock out farther as well. The tube really needs to come pretty straight out for about the first inch before turning. A good rule is if you can get a deep socket on the rear bolt of each tube, you have a pretty good shot
I'm more than just skeptical. As your image shows, the tubes turn toward the rear upon exit. Headers for P heads need to go down upon exit, then back. If the headers you show were attached to P heads, the plugs would go straight into the tubes. It would take a lot more than 1/4" spacers to fix that.
 

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HiPo's have been done with just a small bit of spark plug clearance grinding on #8.

View attachment 761471
Many of these pictures can be misleading... you still have to consider putting a jacket around the spark plug or when you change them - a socket and wrench. The #6, 7 and 8 plugs look like they would not be able to get a plug wire on them or if you did it would be right up on the header which will burn the wire. I love the GT40P heads - I built my engine with them. If you want lots of power and affordability then they are the ticket but plan upon building your own headers if you don't want to break the bank on the aftermarket ones.
 

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I'm more than just skeptical. As your image shows, the tubes turn toward the rear upon exit. Headers for P heads need to go down upon exit, then back. If the headers you show were attached to P heads, the plugs would go straight into the tubes. It would take a lot more than 1/4" spacers to fix that.

Those are P heads and those are the headers I'm running on them. I didn't have to massage any tubes either. It's just #7&8 that are a little tight for service. I'm using 90° boots
 

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Stock manifolds with a little grinding work. Personally I'm skeptical the K exhaust manifold flows any better. They both have the same 2" outlet. I did see a comparison on the same car on the same day on the same chassis dyno where stock, K code and try y headers were tested on a 2.25" system. The stock and K code manifolds made exactly the same power. The try y made something like 15 hp at the wheels.
 

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Dimples
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Discussion Starter #18
Those are P heads and those are the headers I'm running on them. I didn't have to massage any tubes either. It's just #7&8 that are a little tight for service. I'm using 90° boots
I forgot to include that bit of info, but 90° boots were mentioned as part of this hack.
 

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I would say it might work. On SOME cars and SOME headers. I had a GT40P on the stand for a while and tried all of my collection of headers, short, long, some for Foxes even, no. Borrowed some mid-lengths and another set from friends. No chance of fitting. Then like I don't enough enough junky headers around I bought some unknown long tubes reputedly from a "289 Mustang". Fit straight on. I would grind a little bit of flange for spark plug clearance but other than that, right on. Just going by my memory of when I was fiddling with various headers I believe that some could be spaced out effectively and on some it would be a waste of time. No hard and fast rule.
 
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Issues I see:
  • I am not sure I have seen hex head header bolts that would be long enough.
  • I doubt there is room in a 65-66 engine bay
  • Fighting to slip one header gasket in can be a task, now two gaskets and a rigid spacer?
  • Seems far more likely to leak
 
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