Difference between stock heads and GT-40P's?

Shotgun28 · 01-18-2001, 12:18 AM

I was trying to figure out in relation to size why my Flowtech headers will work on my stock heads, but won't (supposedly) work with the GT-40's? what exactly is the difference. If anyone uses Flowtech Headers, what Heads will work? Thanks everyone...

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91 LX Convertible Gray on Red B&M Shift improver kit, March underdrive pulley's Richmond 3.73 gears, 1 5/8 Flowtech long tube Headers and off road h-pipe, Flowmaster 2-chamber cat-back with S.S exhaust, MSD 6A Ignition with coil,Cap and rotor, Taylor Pro wires, K&N 12" conical filter system, Jet stage 2 performance chip and Lentech Street Terminator plus on it's way...just ordered some new Red alum pulley's. Doing some big shopping of late, I will keep you posted.

Shotgun28 · 01-18-2001, 01:40 AM

A penny for your thoughts please......

------------------
91 LX Convertible Gray on Red B&M Shift improver kit, March underdrive pulley's Richmond 3.73 gears, 1 5/8 Flowtech long tube Headers and off road h-pipe, Flowmaster 2-chamber cat-back with S.S exhaust, MSD 6A Ignition with coil,Cap and rotor, Taylor Pro wires, K&N 12" conical filter system, Jet stage 2 performance chip and Lentech Street Terminator plus on it's way...just ordered some new Red alum pulley's. Doing some big shopping of late, I will keep you posted.

Mach 1 · 01-18-2001, 05:49 AM

They will work on the GT40's, but not the GT40-P's. This is simply because they dont fit correctly, because the gt40p has a different design. They will fit on most any other small block ford head that is compatible with your stock heads(trick flow, edelbrock, etc...)

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1993 GT/AOD
'93 Mustang GT

Jeff Chambers · 01-18-2001, 07:34 AM

Most of the problem is created by the repositioned sparkplug. With the P heads, the sparkplug is canted into the combustion chamber at a different angle that causes some problems with stock type headers. With some headers, you're fine on six out of eight cylinders but those last two require the use of a shorty spark plug (like Accel) to clear the primary.

Coast High Performance/Pro Mustang were susposed to start making a P specific long tube header. You could contact them to see if they've started shipping yet.

------------------
Jeff Chambers
Trophy Stock #3
11.97 Seconds / 114.5 MPH
Chambers Racing Team

Josh91 · 01-18-2001, 10:36 AM

Jeff is right on. They will not fit because the spark plug is rotated in and up (towards center of combustion chamber). This places the spark plug very close to the header primaries. Most headers start the downward turn too soon and the result is burnt plug wires. The P specific headers extend from the head a couple of inches more before turning down. This allows plenty of clearance for the plug wires.

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1991 Mustang GT - Cobra Intake, FMS 65mm TB, C&L 73mm MAF, GT-40P heads, Crane 2031 cam, Crane 1.7rr, Built AOD, Art Carr 2400 non-lockup converter, Transgo shift kit, BBK chrome cold air, FMS 'P' headers, Pacesetter off-road H, BBK aluminum pulleys, 2-C Flows w/ dumps, 4.10's, Steeda STB, for now...

The Original GT-40P Tech Page

Shotgun28 · 01-18-2001, 10:59 AM

Does anyone have any info on the gt-40p headers used with these heads, they look stock and I am worried they will not flow as well as my present headers, I really liked the heads, but I would hate to replace my present set-up which is only 3 months old, I think I would have to replace both my headers and h-pipe, is it worth it? Cost wise, I could pick up a set of World Windsor or Edelbrock and not have this conflict. Any ideas?

------------------
91 LX Convertible Gray on Red B&M Shift improver kit, March underdrive pulley's Richmond 3.73 gears, 1 5/8 Flowtech long tube Headers and off road h-pipe, Flowmaster 2-chamber cat-back with S.S exhaust, MSD 6A Ignition with coil,Cap and rotor, Taylor Pro wires, K&N 12" conical filter system, Jet stage 2 performance chip and Lentech Street Terminator plus on it's way...just ordered some new Red alum pulley's. Doing some big shopping of late, I will keep you posted.

Josh91 · 01-18-2001, 01:01 PM

The Mac and Ford shorty headers that are P specific are both 1 5/8 headers just like any other aftermarket header. I'm not sure about your H-pipe, but if it is a ball and socket type, then you can use any longtube header with it. Again, if you are set on using your exhaust setup, you may want to consider some used GT-40 irons or the Windsor Jr's. Of course, the Windsor Jr's require stud mount roller rockers, so there is extra cost associated with them. You will probably need hardened pushrods with them also. The GT-40 irons will accept everything you have now, no changes needed except a different spark plug I think. Even if you did decide to go with the Windsor's or the Edelbrocks, they are at least $500 more than the P's and a new exhaust setup (new headers and H pipe) is only going to set you back around $350 or so. Plus, you can sell your Flowtech stuff afterwards. Another side note is that the only long tube that will work with the P's is the Mac longtubes, who is also the only company besides Flowtech that makes a longtube header for AOD stangs.

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1991 Mustang GT - Cobra Intake, FMS 65mm TB, C&L 73mm MAF, GT-40P heads, Crane 2031 cam, Crane 1.7rr, Built AOD, Art Carr 2400 non-lockup converter, Transgo shift kit, BBK chrome cold air, FMS 'P' headers, Pacesetter off-road H, BBK aluminum pulleys, 2-C Flows w/ dumps, 4.10's, Steeda STB, for now...

The Original GT-40P Tech Page

Shotgun28 · 01-18-2001, 01:21 PM

JOSH91:

Thank you for all of the info, I see that you have the GT-40P heads and I was wondering if you like them, and was there a good increase in h.p and torque? I believe my h-pipe is a shorter h-pipe than usual to go with my present headers. So in essence I am trying to dsecide if the change is worth it. I figure after all is said and done, I will be paying roughly the same for the GT-40P heads with header and new h-pipe, for a new set of edelbrock or another after market head, and I am just trying to see if you like your present set-up, your set-up is very much like what I am planning with a few changes here and there.Central Coast Mustang has a deal with the heads,headers and cobra intake and I was thinking would that combo work well? Thanks for all your help.

------------------
91 LX Convertible Gray on Red B&M Shift improver kit, March underdrive pulley's Richmond 3.73 gears, 1 5/8 Flowtech long tube Headers and off road h-pipe, Flowmaster 2-chamber cat-back with S.S exhaust, MSD 6A Ignition with coil,Cap and rotor, Taylor Pro wires, K&N 12" conical filter system, Jet stage 2 performance chip and Lentech Street Terminator plus on it's way...just ordered some new Red alum pulley's. Doing some big shopping of late, I will keep you posted.

Josh91 · 01-18-2001, 02:29 PM

I am VERY happy with my combo! The only thing I would do different is to get longtube headers, which is what I am going to do soon. I have found some Mac's that are barely used and I am going to get those. Other than that, I am pleased with the P's. It gave me quite a bit of an increase. I don't have any numbers to back it up right now, but my SOTP meter says it is quite a lot. Longtubes take an H pipe that is made for LT's, but they are usually interchangeable with other headers, unless Flowtech makes them so that they only work with their header. Central Coasts deal on heads/headers/intake/roller rockers is a pretty good deal if you have the money. Plus, you figure the P's + new exhaust will be around $800 - $900 for the whole thing. The Ebok's will cost you $1000 just by themselves. The main reasons I went with the P's are because of the great power they make and the cost. Plus, I only had stock headers before so new headers wasn't an issue for me. Also, by getting the P's it allowed me money for a cam, which I really wanted.

------------------
1991 Mustang GT - Cobra Intake, FMS 65mm TB, C&L 73mm MAF, GT-40P heads, Crane 2031 cam, Crane 1.7rr, Built AOD, Art Carr 2400 non-lockup converter, Transgo shift kit, BBK chrome cold air, FMS 'P' headers, Pacesetter off-road H, BBK aluminum pulleys, 2-C Flows w/ dumps, 4.10's, Steeda STB, for now...

The Original GT-40P Tech Page

1989GT · 01-18-2001, 04:31 PM

If you really want the P's your best bet is to get the headers that are made for them. Some headers will work...but is it worth the trouble? I had stock exhaust when I got the P's so it wasn't a big deal to get new headers. But you can probably sell your set up pretty easily. Since it's only 3 months old it should still be in good shape. I really like the heads. The car pulls really hard down low but it also pulls really hard to the rev-limiter. What ever you decide to do you'll be happy. Just because the car will be sooo much faster. IF you do get the P's make sure you clean them up(Port 'em) it'll be worth it. I wish I had so I'm getting ready to pull the motor apart(again) to port them. Good luck!

------------------
89GT,T-5Z, D.S.S. 306 shortblock w\main support, B-303 cam, Cobra intake, GT40P heads, 1.72rr, MAC "P" headers, MAC off-road H-Pipe, MAC true-fit w\tips, 373's...and the list goes on!
Throttle Junkie Powered by Ford!
12.824 @ 107.05 MPH

White5.0 · 01-18-2001, 10:59 PM

if im correct the gt40p heads are what comes on the ford explorer with a 5.0 engine, if you can find headers for a explorer they should bolt up. not sure but i will look into this more,

Shotgun28 · 01-20-2001, 12:47 AM

Thanks White 5.0 , let me know what you find out...My only concern is whether or not the Mac long tubes will work on the P heads, I know for a fact my h-pipe is a short h-pipe and should work with them, but will they fit the p heads? Thanks everyone....If not I will just get the regular headers made for the P heads and get another h-pipe and sell my present headers and h-pipe. Central coast is selling the P heads with 1.7 cobra roller rockers for $799, is this a good deal and them with the Cobra intake $1067....Sounds like another good option, because they are also selling a 65mm Ford Throttle body for only $127...Good deal indeed. I think they would all compliment each other..

------------------
91 LX Convertible Gray on Red B&M Shift improver kit, March underdrive pulley's Richmond 3.73 gears, 1 5/8 Flowtech long tube Headers and off road h-pipe, Flowmaster 2-chamber cat-back with S.S exhaust, MSD 6A Ignition with coil,Cap and rotor, Taylor Pro wires, K&N 12" conical filter system, Jet stage 2 performance chip and Lentech Street Terminator plus on it's way...just ordered some new Red alum pulley's. Doing some big shopping of late, I will keep you posted.

01-18-2001, 12:18 AM	#1
Shotgun28 Registered Member Join Date: Sep 2000 Location: New Hope MN USA Posts: 276	Difference between stock heads and GT-40P's? I was trying to figure out in relation to size why my Flowtech headers will work on my stock heads, but won't (supposedly) work with the GT-40's? what exactly is the difference. If anyone uses Flowtech Headers, what Heads will work? Thanks everyone... ------------------ 91 LX Convertible Gray on Red B&M Shift improver kit, March underdrive pulley's Richmond 3.73 gears, 1 5/8 Flowtech long tube Headers and off road h-pipe, Flowmaster 2-chamber cat-back with S.S exhaust, MSD 6A Ignition with coil,Cap and rotor, Taylor Pro wires, K&N 12" conical filter system, Jet stage 2 performance chip and Lentech Street Terminator plus on it's way...just ordered some new Red alum pulley's. Doing some big shopping of late, I will keep you posted.

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01-18-2001, 01:40 AM	#2
Shotgun28 Registered Member Join Date: Sep 2000 Location: New Hope MN USA Posts: 276	A penny for your thoughts please...... ------------------ 91 LX Convertible Gray on Red B&M Shift improver kit, March underdrive pulley's Richmond 3.73 gears, 1 5/8 Flowtech long tube Headers and off road h-pipe, Flowmaster 2-chamber cat-back with S.S exhaust, MSD 6A Ignition with coil,Cap and rotor, Taylor Pro wires, K&N 12" conical filter system, Jet stage 2 performance chip and Lentech Street Terminator plus on it's way...just ordered some new Red alum pulley's. Doing some big shopping of late, I will keep you posted.

01-18-2001, 05:49 AM	#3
Mach 1 Registered Member Join Date: May 1999 Location: Georgia Posts: 3,866	They will work on the GT40's, but not the GT40-P's. This is simply because they dont fit correctly, because the gt40p has a different design. They will fit on most any other small block ford head that is compatible with your stock heads(trick flow, edelbrock, etc...) ------------------ 1993 GT/AOD '93 Mustang GT

01-18-2001, 07:34 AM	#4
Jeff Chambers Moderator Join Date: Aug 2000 Location: Milan, OH Posts: 2,699	Most of the problem is created by the repositioned sparkplug. With the P heads, the sparkplug is canted into the combustion chamber at a different angle that causes some problems with stock type headers. With some headers, you're fine on six out of eight cylinders but those last two require the use of a shorty spark plug (like Accel) to clear the primary. Coast High Performance/Pro Mustang were susposed to start making a P specific long tube header. You could contact them to see if they've started shipping yet. ------------------ Jeff Chambers Trophy Stock #3 11.97 Seconds / 114.5 MPH Chambers Racing Team

01-18-2001, 10:36 AM	#5
Josh91 Registered Member Join Date: Nov 1998 Location: Salina, KS Posts: 83	Jeff is right on. They will not fit because the spark plug is rotated in and up (towards center of combustion chamber). This places the spark plug very close to the header primaries. Most headers start the downward turn too soon and the result is burnt plug wires. The P specific headers extend from the head a couple of inches more before turning down. This allows plenty of clearance for the plug wires. ------------------ 1991 Mustang GT - Cobra Intake, FMS 65mm TB, C&L 73mm MAF, GT-40P heads, Crane 2031 cam, Crane 1.7rr, Built AOD, Art Carr 2400 non-lockup converter, Transgo shift kit, BBK chrome cold air, FMS 'P' headers, Pacesetter off-road H, BBK aluminum pulleys, 2-C Flows w/ dumps, 4.10's, Steeda STB, for now... The Original GT-40P Tech Page

01-18-2001, 10:59 AM	#6
Shotgun28 Registered Member Join Date: Sep 2000 Location: New Hope MN USA Posts: 276	Does anyone have any info on the gt-40p headers used with these heads, they look stock and I am worried they will not flow as well as my present headers, I really liked the heads, but I would hate to replace my present set-up which is only 3 months old, I think I would have to replace both my headers and h-pipe, is it worth it? Cost wise, I could pick up a set of World Windsor or Edelbrock and not have this conflict. Any ideas? ------------------ 91 LX Convertible Gray on Red B&M Shift improver kit, March underdrive pulley's Richmond 3.73 gears, 1 5/8 Flowtech long tube Headers and off road h-pipe, Flowmaster 2-chamber cat-back with S.S exhaust, MSD 6A Ignition with coil,Cap and rotor, Taylor Pro wires, K&N 12" conical filter system, Jet stage 2 performance chip and Lentech Street Terminator plus on it's way...just ordered some new Red alum pulley's. Doing some big shopping of late, I will keep you posted.

01-18-2001, 01:01 PM	#7
Josh91 Registered Member Join Date: Nov 1998 Location: Salina, KS Posts: 83	The Mac and Ford shorty headers that are P specific are both 1 5/8 headers just like any other aftermarket header. I'm not sure about your H-pipe, but if it is a ball and socket type, then you can use any longtube header with it. Again, if you are set on using your exhaust setup, you may want to consider some used GT-40 irons or the Windsor Jr's. Of course, the Windsor Jr's require stud mount roller rockers, so there is extra cost associated with them. You will probably need hardened pushrods with them also. The GT-40 irons will accept everything you have now, no changes needed except a different spark plug I think. Even if you did decide to go with the Windsor's or the Edelbrocks, they are at least $500 more than the P's and a new exhaust setup (new headers and H pipe) is only going to set you back around $350 or so. Plus, you can sell your Flowtech stuff afterwards. Another side note is that the only long tube that will work with the P's is the Mac longtubes, who is also the only company besides Flowtech that makes a longtube header for AOD stangs. ------------------ 1991 Mustang GT - Cobra Intake, FMS 65mm TB, C&L 73mm MAF, GT-40P heads, Crane 2031 cam, Crane 1.7rr, Built AOD, Art Carr 2400 non-lockup converter, Transgo shift kit, BBK chrome cold air, FMS 'P' headers, Pacesetter off-road H, BBK aluminum pulleys, 2-C Flows w/ dumps, 4.10's, Steeda STB, for now... The Original GT-40P Tech Page

01-18-2001, 01:21 PM	#8
Shotgun28 Registered Member Join Date: Sep 2000 Location: New Hope MN USA Posts: 276	JOSH91: Thank you for all of the info, I see that you have the GT-40P heads and I was wondering if you like them, and was there a good increase in h.p and torque? I believe my h-pipe is a shorter h-pipe than usual to go with my present headers. So in essence I am trying to dsecide if the change is worth it. I figure after all is said and done, I will be paying roughly the same for the GT-40P heads with header and new h-pipe, for a new set of edelbrock or another after market head, and I am just trying to see if you like your present set-up, your set-up is very much like what I am planning with a few changes here and there.Central Coast Mustang has a deal with the heads,headers and cobra intake and I was thinking would that combo work well? Thanks for all your help. ------------------ 91 LX Convertible Gray on Red B&M Shift improver kit, March underdrive pulley's Richmond 3.73 gears, 1 5/8 Flowtech long tube Headers and off road h-pipe, Flowmaster 2-chamber cat-back with S.S exhaust, MSD 6A Ignition with coil,Cap and rotor, Taylor Pro wires, K&N 12" conical filter system, Jet stage 2 performance chip and Lentech Street Terminator plus on it's way...just ordered some new Red alum pulley's. Doing some big shopping of late, I will keep you posted.

01-18-2001, 02:29 PM	#9
Josh91 Registered Member Join Date: Nov 1998 Location: Salina, KS Posts: 83	I am VERY happy with my combo! The only thing I would do different is to get longtube headers, which is what I am going to do soon. I have found some Mac's that are barely used and I am going to get those. Other than that, I am pleased with the P's. It gave me quite a bit of an increase. I don't have any numbers to back it up right now, but my SOTP meter says it is quite a lot. Longtubes take an H pipe that is made for LT's, but they are usually interchangeable with other headers, unless Flowtech makes them so that they only work with their header. Central Coasts deal on heads/headers/intake/roller rockers is a pretty good deal if you have the money. Plus, you figure the P's + new exhaust will be around $800 - $900 for the whole thing. The Ebok's will cost you $1000 just by themselves. The main reasons I went with the P's are because of the great power they make and the cost. Plus, I only had stock headers before so new headers wasn't an issue for me. Also, by getting the P's it allowed me money for a cam, which I really wanted. ------------------ 1991 Mustang GT - Cobra Intake, FMS 65mm TB, C&L 73mm MAF, GT-40P heads, Crane 2031 cam, Crane 1.7rr, Built AOD, Art Carr 2400 non-lockup converter, Transgo shift kit, BBK chrome cold air, FMS 'P' headers, Pacesetter off-road H, BBK aluminum pulleys, 2-C Flows w/ dumps, 4.10's, Steeda STB, for now... The Original GT-40P Tech Page

01-18-2001, 04:31 PM	#10
1989GT Registered Member Join Date: Apr 1999 Location: Cincinnati,OH Posts: 1,511	If you really want the P's your best bet is to get the headers that are made for them. Some headers will work...but is it worth the trouble? I had stock exhaust when I got the P's so it wasn't a big deal to get new headers. But you can probably sell your set up pretty easily. Since it's only 3 months old it should still be in good shape. I really like the heads. The car pulls really hard down low but it also pulls really hard to the rev-limiter. What ever you decide to do you'll be happy. Just because the car will be sooo much faster. IF you do get the P's make sure you clean them up(Port 'em) it'll be worth it. I wish I had so I'm getting ready to pull the motor apart(again) to port them. Good luck! ------------------ 89GT,T-5Z, D.S.S. 306 shortblock w\main support, B-303 cam, Cobra intake, GT40P heads, 1.72rr, MAC "P" headers, MAC off-road H-Pipe, MAC true-fit w\tips, 373's...and the list goes on! Throttle Junkie Powered by Ford! 12.824 @ 107.05 MPH

01-18-2001, 10:59 PM	#11
White5.0 Registered Member Join Date: Dec 2000 Location: VA Posts: 80	if im correct the gt40p heads are what comes on the ford explorer with a 5.0 engine, if you can find headers for a explorer they should bolt up. not sure but i will look into this more,

01-20-2001, 12:47 AM	#12
Shotgun28 Registered Member Join Date: Sep 2000 Location: New Hope MN USA Posts: 276	Thanks White 5.0 , let me know what you find out...My only concern is whether or not the Mac long tubes will work on the P heads, I know for a fact my h-pipe is a short h-pipe and should work with them, but will they fit the p heads? Thanks everyone....If not I will just get the regular headers made for the P heads and get another h-pipe and sell my present headers and h-pipe. Central coast is selling the P heads with 1.7 cobra roller rockers for $799, is this a good deal and them with the Cobra intake $1067....Sounds like another good option, because they are also selling a 65mm Ford Throttle body for only $127...Good deal indeed. I think they would all compliment each other.. ------------------ 91 LX Convertible Gray on Red B&M Shift improver kit, March underdrive pulley's Richmond 3.73 gears, 1 5/8 Flowtech long tube Headers and off road h-pipe, Flowmaster 2-chamber cat-back with S.S exhaust, MSD 6A Ignition with coil,Cap and rotor, Taylor Pro wires, K&N 12" conical filter system, Jet stage 2 performance chip and Lentech Street Terminator plus on it's way...just ordered some new Red alum pulley's. Doing some big shopping of late, I will keep you posted.