GT-40 irons

RobertD · 06-02-2001, 05:41 PM

Anybody know where to get some GT-40 irons? I've been going crazy looking for them. After all of the stories of Edelbrocks wearing the spring shims, Holley's burning oil, and loss of low end torque with any other heads, I'm kinda leaning towards these. Obviously, I'd like stone reliability.

------------------
Robert
91GT; 88 ASC McLaren #709

06-02-2001, 05:51 PM

Forget the GT-40's and look for the GT-40P heads. They'll make more power and are alot more readily available.

------------------
Jeff Chambers
T/S #3
11.611 Seconds/116.7 MPH
Chambers Racing Team

RobertD · 06-02-2001, 06:25 PM

My only argument is that I'd have to buy $200 headers to go with them. If I'm going to lay out that kind of cash ($600+$200) I'd be better off getting the aluminum GT-40's. Which is where I may end up.

Lexicon · 06-02-2001, 08:28 PM

Your best bet is to get a copy of a mustang publication and start calling some of the advertisers, you may get lucky in locating a set. Maybe your local speedshop will have the low down on a set from other customers.

You could find a set of used 351 heads from (I believe 76 and up) maybe an entire longblock and find a local shop to machine the heads and perform all the port and bowel work for a good price. A good deal of the publications stay away from this advice due to the money involved, but if you are set on an iron head with GT-40 specs then a 351 head would be a great place to start. Hopefully you have access to good machinist and fair pricing. Then you could top the head with your choice of valvetrain components. You would have the added bonus of doing some of the work yourself, if you are into the "hot rodding" image and don't wish to go the shop and bolt route. Nothing wrong with that, but just in case you wanted to follow a different route.

[This message has been edited by Lexicon (edited 06-02-2001).]

Unit 5302 · 06-02-2001, 10:20 PM

While the GT-40 Iron heads are significantly better than the stock units, they are not really worth the kind of money you'd spend to upgrade.

There are some drawbacks to the GT-40 iron heads. One major one is the combustion chamber size. At 65.5cc's it'll drop your compression down to about 8.8:1 from 9.0:1.

The GT-40 doesn't flow exceptionally well at low lifts either. It's much like the Windsor Jr's and Sr's in that regard. They are very linear in the way the flow increases. Quite frankly, after looking at the flow numbers, I'm completely unimpressed with all three of those heads in stock form.

Expect max flow out of the GT40's to be about 190cfm intake, and about 130cfm exhaust. Even with the larger than stock (and GT-40P) exhaust valves, the GT-40 iron seems to be deficient on exhaust flow.

Valve sizes on the

GT-40 iron are 1.84" 1.54"
GT-40P 1.84" 1.46"
E7TE 1.78" 1.46"

The GT-40P heads make much better flow numbers at lower lifts, in addition they feature 59cc combustion chambers that will effectively raise your compression ratio to about 9.5:1.

Coupled with the additional compression, and the additional lower lift flow (equal flow from about .400-.600) the GT-40P is significantly superior to the GT-40 Iron heads, and they are a great head with just a little exhaust work to get up to a better 80% of intake exhaust flow.

I've also heard of deals as good as $400 for a complete set of GT-40P heads. It may be worth calling around in your area to locate a 1996-2001 Ford Explorer with the 5.0. If you can get a solid deal on the Explorer V-8's 5.0, you could be setting yourself up with a solid deal for performance. The 5.0 in the Explorer also comes with the Explorer intake, (GT-40 Lower/Explorer (nearly the same as the Cobra) upper.)

RobertD · 06-02-2001, 11:35 PM

Well, You kinda pushed me back to the 40p's again. I had originally thought about getting them! I guess that airflow "under the curve" is alot more important than peak. The 40P's seem to get that air flowing right away.

It doesn't sound like a bad combo...A 306 (my engine rebuilt) with a mild cam, GT-40P's, a Cobra intake and an off-road exhaust. If I get the tune right I should be making some decent power.

What I'm really looking for is a reliable combo that will make some good power. It'll be kept below 5500 RPM's and I would like some great torque.

You guys have me thinking...

------------------
Robert
91GT; 88 ASC McLaren #709

Unit 5302 · 06-03-2001, 02:56 PM

GT-40P heads, lightly port exhaust
E-303 cam,
Explorer or Cobra intake.

That combo is capable of making 320hp, and it'll keep your power band long and strong.

Check on Ebay, I've seen good deals on used Cobra and Explorer intakes.

Francismaximus · 06-04-2001, 08:30 PM

Where in the world did you get your flow #'s from. The gt 4o's flow better then p's al over unless the p's are ported. Plus the p's lose exaust flow due to smaller valve at 400-500 lift. The p's only have a velocity advantange but not enough to outweigh the benifits of the GT-40's

------------------

Unit 5302 · 06-04-2001, 11:49 PM

Courtesy of Fletch's Carbureted 5.0L webpage

Intake Flow @ 28" H20

.100" .200" .300" .400" .500"
GT-40P 61 128 169 195 196
GT-40 54 107 157 183 192
E7TE 59 114 144 156 156
'69 351W 52 103 149 174 183
289 50 97 127 156 165
GT-40Y 64 114 167 199 213
GT-40X 53 114 170 207 226

Exhaust Flow @ 28" H20

.100" .200" .300" .400" .500"
GT-40P 52 90 123 135 139
GT-40 47 94 119 128 128
E7TE 42 78 105 115 116
'69 351W 48 77 100 113 118
289 37 71 93 104 107
GT-40Y 52 98 128 137 134
GT-40X 50 106 139 153 161

Courtesy of FordMuscle.com

GT40P .100 .200 .300 .400 .500 .600
Intake 61 125 166 195 196 190
Exhaust 50 89 120 132 138 144
http://home.isoa.net/~mharrisj/fordhead.html
http://www.geocities.com/motorcitymustang/gt40p.html
http://www.fordmuscle.com/archives/2...s/index1.shtml

As you can see, FordMuscle.com got basically the same flow numbers as the above page.

The GT-40P kicks the GT-40 Iron's *** quite frankly.

What possibly possessed you to step and and talk about stuff you obviously don't know about? It's widely held that the GT-40P or 2nd GEN GT-40 head flows significantly better than the original GT-40.

I spent a good week researching the heads, flow numbers, and reasons for the GT-40P heads begin better. I originally thought the GT-40 heads would have been better, but I never stepped in telling people they were wrong without researching like you just did.

The GT-40P's eliminate most of the thermactor bump that chokes off exhaust flow, the ports are designed for increased flow velocity (more flow to people who don't know what that equates to), a smaller combustion chamber (increased compression about 3/4 of a point) further adding hp.

You're an idiot if you think the GT-40 outflows the P on the exhaust side between 400-500 lift. See above reference to the thermactor bump. Also see above reference to better port velocity thanks to redesigned intake and exhaust ports.

You really need to research your **** before you come in here spreading misinformation.

red82gt · 06-05-2001, 02:47 AM

In MM&FF june issue the GT-40 beat the GT-40p throught the entire range for intake and exhaust.
For comparison, my GT-40 irons (Fox Lake, stage III ported) peaked at 241cfm int@.600
and 198cfm@.600! These heads really like a port job but the iron is hard to port and a job like this costs a pretty penny.

------------------
GT-40 heads (ported, polished, + milled), B303 cam, 1.7rr's, JE pistons, Offy intake, Carter AFB 625cfm carb, Flowtech 1 5/8" shortys, Flowtech X-pipe, MAC Flowpath exhaust, MAC pulleys, 373's, subframes, Eibachs+Tokicos, B&M ripper, FMS Clutch, Zoom Quadrant+cable, 17" CSA Ultra rims, 235/45ZR17 Yokohama AVS S4's, MSD 6A ignition+coil, FMS 9mm wires, Carbed, Naturally Aspirated, and Nasty!

[This message has been edited by red82gt (edited 06-05-2001).]

Francismaximus · 06-05-2001, 06:51 AM

Buddy I work for ford the GT-40
s A: flow much better after being cleaned up B: the P;s just dod a little better stock cause of small runners and velocity. ANd the small exayst valve will ALWAYS hurt as you step up the power. Yeah the GT40p gets it in but EXCUSE ME hows it get out. ITS a fricken truck head thats ford needed bottom end torque in to pull a 45oo pd truck. You got the p. You want a Cobra that spins to 5500 rpm and makes power up there ford dud out the old castings for the gt40's. Go read a nother magazine buddy. I DONT KNOW WHAT IM TALKING ABOUT. OK go get p's then feed this myth and make some special header company rich! I'll buy used cheap GT-40's and see-ya at the track!

------------------

Jeff Chambers · 06-05-2001, 08:35 AM

I can speak from what I've seen running in competition. Nearly everyone (90% or more) running competitively in T/S has switched to the P head because it just flat-out makes more power. Flow numbers aren't everything. The combustion chamber in the P's is superior, the exhaust port is superior, the spark plug placement is superior, and the deck thickness is superior, just to name a few.

We run the heads un-ported with a small (.500") cam, either carbed or EFI, and we've got guys making 340-370RWHP. You do the math, that means 425+ at the crank. Not a small feat. That's with shorty headers and stock sized valves too. I've had both GT-40 and GT-40P heads prepped basically the same way (gasket matched to 1250 and 1415 gaskets) and even though the flow numbers were very close, the P's make abundantly more HP. I think their key is runner velocity...they absolutely love it and its what makes the small valves work.

Don't discount them if you're in the market for iron heads. With a nearly endless supply of them at $200 a pair (bare), they're a very economical HP bolt-on.

Look at the guys running in Pure Street too. Tom Payne set the record last year at 11.09@122+ with a set of P heads.

Just my $0.05.

------------------
Jeff Chambers
Trophy Stock #3
11.611 Seconds / 116.7 MPH
Chambers Racing Team

95mustanggt · 06-05-2001, 12:32 PM

Dam you Chambers!

I had just decided on a pair of Edelbrock head, and you've sold the idea of the GT-40P's on me and now I've changed my mind again! Bastard

Oh and what intake matches the GT-40P real well, the Cobra?

This stuff can be so confusing some times...

------------------
Driving: 1998 F-150
Far way in Edmonton==>

1995 Mustang GT

Jeff Chambers · 06-05-2001, 12:53 PM

Darn near any intake will work with the 1250's. GT-40, Cobra, Explort, Edelbrock Performer & Performer RPM, TFS, Holley; etc. You name it and it'll almost absitively, positutely fit. I've got a GT-40 system for sale right now; upper & lower, 1/2" spacer, new gaskets and all the bolts (I just upgraded to a Performer RPM). Best yet, the manifolds are already gasket matched and milled so they'll work real well with a set of heartily prepped GT-40P's. Any takers? I've even got real recent flow numbers on the combination.

------------------
Jeff Chambers
Trophy Stock #3
11.611 Seconds / 116.7 MPH
Chambers Racing Team

mgranzow · 06-05-2001, 02:37 PM

hey, i know they aren't irons, but what about the GT40X heads??? how do they stack up against the p or the plain gt40's?

06-02-2001, 05:41 PM	#1 (permalink)
RobertD Registered Member Join Date: Jun 1999 Location: El Paso, Texas, USA Posts: 170	GT-40 irons Anybody know where to get some GT-40 irons? I've been going crazy looking for them. After all of the stories of Edelbrocks wearing the spring shims, Holley's burning oil, and loss of low end torque with any other heads, I'm kinda leaning towards these. Obviously, I'd like stone reliability. ------------------ Robert 91GT; 88 ASC McLaren #709

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06-02-2001, 05:51 PM	#2 (permalink)
jchambers Posts: n/a	Forget the GT-40's and look for the GT-40P heads. They'll make more power and are alot more readily available. ------------------ Jeff Chambers T/S #3 11.611 Seconds/116.7 MPH Chambers Racing Team

06-02-2001, 06:25 PM	#3 (permalink)
RobertD Registered Member Join Date: Jun 1999 Location: El Paso, Texas, USA Posts: 170	My only argument is that I'd have to buy $200 headers to go with them. If I'm going to lay out that kind of cash ($600+$200) I'd be better off getting the aluminum GT-40's. Which is where I may end up.

06-02-2001, 08:28 PM	#4 (permalink)
Lexicon Registered Member Join Date: Jun 1999 Location: Evansville, Indiana Posts: 182	Your best bet is to get a copy of a mustang publication and start calling some of the advertisers, you may get lucky in locating a set. Maybe your local speedshop will have the low down on a set from other customers. You could find a set of used 351 heads from (I believe 76 and up) maybe an entire longblock and find a local shop to machine the heads and perform all the port and bowel work for a good price. A good deal of the publications stay away from this advice due to the money involved, but if you are set on an iron head with GT-40 specs then a 351 head would be a great place to start. Hopefully you have access to good machinist and fair pricing. Then you could top the head with your choice of valvetrain components. You would have the added bonus of doing some of the work yourself, if you are into the "hot rodding" image and don't wish to go the shop and bolt route. Nothing wrong with that, but just in case you wanted to follow a different route. [This message has been edited by Lexicon (edited 06-02-2001).]

06-02-2001, 10:20 PM	#5 (permalink)
Unit 5302 Registered Member Join Date: May 1999 Posts: 5,237	While the GT-40 Iron heads are significantly better than the stock units, they are not really worth the kind of money you'd spend to upgrade. There are some drawbacks to the GT-40 iron heads. One major one is the combustion chamber size. At 65.5cc's it'll drop your compression down to about 8.8:1 from 9.0:1. The GT-40 doesn't flow exceptionally well at low lifts either. It's much like the Windsor Jr's and Sr's in that regard. They are very linear in the way the flow increases. Quite frankly, after looking at the flow numbers, I'm completely unimpressed with all three of those heads in stock form. Expect max flow out of the GT40's to be about 190cfm intake, and about 130cfm exhaust. Even with the larger than stock (and GT-40P) exhaust valves, the GT-40 iron seems to be deficient on exhaust flow. Valve sizes on the GT-40 iron are 1.84" 1.54" GT-40P 1.84" 1.46" E7TE 1.78" 1.46" The GT-40P heads make much better flow numbers at lower lifts, in addition they feature 59cc combustion chambers that will effectively raise your compression ratio to about 9.5:1. Coupled with the additional compression, and the additional lower lift flow (equal flow from about .400-.600) the GT-40P is significantly superior to the GT-40 Iron heads, and they are a great head with just a little exhaust work to get up to a better 80% of intake exhaust flow. I've also heard of deals as good as $400 for a complete set of GT-40P heads. It may be worth calling around in your area to locate a 1996-2001 Ford Explorer with the 5.0. If you can get a solid deal on the Explorer V-8's 5.0, you could be setting yourself up with a solid deal for performance. The 5.0 in the Explorer also comes with the Explorer intake, (GT-40 Lower/Explorer (nearly the same as the Cobra) upper.)

06-02-2001, 11:35 PM	#6 (permalink)
RobertD Registered Member Join Date: Jun 1999 Location: El Paso, Texas, USA Posts: 170	Well, You kinda pushed me back to the 40p's again. I had originally thought about getting them! I guess that airflow "under the curve" is alot more important than peak. The 40P's seem to get that air flowing right away. It doesn't sound like a bad combo...A 306 (my engine rebuilt) with a mild cam, GT-40P's, a Cobra intake and an off-road exhaust. If I get the tune right I should be making some decent power. What I'm really looking for is a reliable combo that will make some good power. It'll be kept below 5500 RPM's and I would like some great torque. You guys have me thinking... ------------------ Robert 91GT; 88 ASC McLaren #709

06-03-2001, 02:56 PM	#7 (permalink)
Unit 5302 Registered Member Join Date: May 1999 Posts: 5,237	GT-40P heads, lightly port exhaust E-303 cam, Explorer or Cobra intake. That combo is capable of making 320hp, and it'll keep your power band long and strong. Check on Ebay, I've seen good deals on used Cobra and Explorer intakes.

06-04-2001, 08:30 PM	#8 (permalink)
Francismaximus Registered Member Join Date: May 2001 Location: Harriman, NY, USA Posts: 11	Where in the world did you get your flow #'s from. The gt 4o's flow better then p's al over unless the p's are ported. Plus the p's lose exaust flow due to smaller valve at 400-500 lift. The p's only have a velocity advantange but not enough to outweigh the benifits of the GT-40's ------------------

06-04-2001, 11:49 PM	#9 (permalink)
Unit 5302 Registered Member Join Date: May 1999 Posts: 5,237	Courtesy of Fletch's Carbureted 5.0L webpage Intake Flow @ 28" H20 .100" .200" .300" .400" .500" GT-40P 61 128 169 195 196 GT-40 54 107 157 183 192 E7TE 59 114 144 156 156 '69 351W 52 103 149 174 183 289 50 97 127 156 165 GT-40Y 64 114 167 199 213 GT-40X 53 114 170 207 226 Exhaust Flow @ 28" H20 .100" .200" .300" .400" .500" GT-40P 52 90 123 135 139 GT-40 47 94 119 128 128 E7TE 42 78 105 115 116 '69 351W 48 77 100 113 118 289 37 71 93 104 107 GT-40Y 52 98 128 137 134 GT-40X 50 106 139 153 161 Courtesy of FordMuscle.com GT40P .100 .200 .300 .400 .500 .600 Intake 61 125 166 195 196 190 Exhaust 50 89 120 132 138 144 http://home.isoa.net/~mharrisj/fordhead.html http://www.geocities.com/motorcitymustang/gt40p.html http://www.fordmuscle.com/archives/2...s/index1.shtml As you can see, FordMuscle.com got basically the same flow numbers as the above page. The GT-40P kicks the GT-40 Iron's * quite frankly. What possibly possessed you to step and and talk about stuff you obviously don't know about? It's widely held that the GT-40P or 2nd GEN GT-40 head flows significantly better than the original GT-40. I spent a good week researching the heads, flow numbers, and reasons for the GT-40P heads begin better. I originally thought the GT-40 heads would have been better, but I never stepped in telling people they were wrong without researching like you just did. The GT-40P's eliminate most of the thermactor bump that chokes off exhaust flow, the ports are designed for increased flow velocity (more flow to people who don't know what that equates to), a smaller combustion chamber (increased compression about 3/4 of a point) further adding hp. You're an idiot if you think the GT-40 outflows the P on the exhaust side between 400-500 lift. See above reference to the thermactor bump. Also see above reference to better port velocity thanks to redesigned intake and exhaust ports. You really need to research your ** before you come in here spreading misinformation.

06-05-2001, 02:47 AM	#10 (permalink)
red82gt Sober voice of Reason Join Date: Nov 1998 Location: Kelowna, B.C., Canada Posts: 1,508	In MM&FF june issue the GT-40 beat the GT-40p throught the entire range for intake and exhaust. For comparison, my GT-40 irons (Fox Lake, stage III ported) peaked at 241cfm int@.600 and 198cfm@.600! These heads really like a port job but the iron is hard to port and a job like this costs a pretty penny. ------------------ GT-40 heads (ported, polished, + milled), B303 cam, 1.7rr's, JE pistons, Offy intake, Carter AFB 625cfm carb, Flowtech 1 5/8" shortys, Flowtech X-pipe, MAC Flowpath exhaust, MAC pulleys, 373's, subframes, Eibachs+Tokicos, B&M ripper, FMS Clutch, Zoom Quadrant+cable, 17" CSA Ultra rims, 235/45ZR17 Yokohama AVS S4's, MSD 6A ignition+coil, FMS 9mm wires, Carbed, Naturally Aspirated, and Nasty! [This message has been edited by red82gt (edited 06-05-2001).]

06-05-2001, 06:51 AM	#11 (permalink)
Francismaximus Registered Member Join Date: May 2001 Location: Harriman, NY, USA Posts: 11	Buddy I work for ford the GT-40 s A: flow much better after being cleaned up B: the P;s just dod a little better stock cause of small runners and velocity. ANd the small exayst valve will ALWAYS hurt as you step up the power. Yeah the GT40p gets it in but EXCUSE ME hows it get out. ITS a fricken truck head thats ford needed bottom end torque in to pull a 45oo pd truck. You got the p. You want a Cobra that spins to 5500 rpm and makes power up there ford dud out the old castings for the gt40's. Go read a nother magazine buddy. I DONT KNOW WHAT IM TALKING ABOUT. OK go get p's then feed this myth and make some special header company rich! I'll buy used cheap GT-40's and see-ya at the track! ------------------

Sponsored Links

06-05-2001, 08:35 AM	#12 (permalink)
Jeff Chambers Moderator Join Date: Aug 2000 Location: Milan, OH Posts: 2,699	I can speak from what I've seen running in competition. Nearly everyone (90% or more) running competitively in T/S has switched to the P head because it just flat-out makes more power. Flow numbers aren't everything. The combustion chamber in the P's is superior, the exhaust port is superior, the spark plug placement is superior, and the deck thickness is superior, just to name a few. We run the heads un-ported with a small (.500") cam, either carbed or EFI, and we've got guys making 340-370RWHP. You do the math, that means 425+ at the crank. Not a small feat. That's with shorty headers and stock sized valves too. I've had both GT-40 and GT-40P heads prepped basically the same way (gasket matched to 1250 and 1415 gaskets) and even though the flow numbers were very close, the P's make abundantly more HP. I think their key is runner velocity...they absolutely love it and its what makes the small valves work. Don't discount them if you're in the market for iron heads. With a nearly endless supply of them at $200 a pair (bare), they're a very economical HP bolt-on. Look at the guys running in Pure Street too. Tom Payne set the record last year at 11.09@122+ with a set of P heads. Just my $0.05. ------------------ Jeff Chambers Trophy Stock #3 11.611 Seconds / 116.7 MPH Chambers Racing Team

06-05-2001, 12:32 PM	#13 (permalink)
95mustanggt Mustang is Parked :( Join Date: May 2000 Location: Kamloops, BC Posts: 2,874	Dam you Chambers! I had just decided on a pair of Edelbrock head, and you've sold the idea of the GT-40P's on me and now I've changed my mind again! Bastard Oh and what intake matches the GT-40P real well, the Cobra? This stuff can be so confusing some times... ------------------ Driving: 1998 F-150 Far way in Edmonton==> 1995 Mustang GT

06-05-2001, 12:53 PM	#14 (permalink)
Jeff Chambers Moderator Join Date: Aug 2000 Location: Milan, OH Posts: 2,699	Darn near any intake will work with the 1250's. GT-40, Cobra, Explort, Edelbrock Performer & Performer RPM, TFS, Holley; etc. You name it and it'll almost absitively, positutely fit. I've got a GT-40 system for sale right now; upper & lower, 1/2" spacer, new gaskets and all the bolts (I just upgraded to a Performer RPM). Best yet, the manifolds are already gasket matched and milled so they'll work real well with a set of heartily prepped GT-40P's. Any takers? I've even got real recent flow numbers on the combination. ------------------ Jeff Chambers Trophy Stock #3 11.611 Seconds / 116.7 MPH Chambers Racing Team

06-05-2001, 02:37 PM	#15 (permalink)
mgranzow Registered Member Join Date: Jun 2001 Location: milwaukee, WI Posts: 9	hey, i know they aren't irons, but what about the GT40X heads??? how do they stack up against the p or the plain gt40's?