GT-40 irons

Unit 5302 · 06-02-2001, 09:20 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.)

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
1988 Gt - 1998 Gt Hp Each Year	steedamustang01	Modular Madness	13	05-09-2002 07:26 PM
1996 Cobra vs 2000 Mustang GT	Milktasd	Stang Stories	2	04-05-2002 03:11 AM
RESULTS - Grand Prix GT vs. Celica GTS	302 LX Eric	Stang Stories	7	09-25-2001 06:46 PM
ran a '01 GT	EZRIDN	Stang Stories	3	08-29-2001 08:17 PM
Just got my '89 GT! Time slip guesses?	84stangLX	Blue Oval Lounge	6	07-25-2001 09:44 PM

06-02-2001, 09:20 PM	#5
Unit 5302 Registered Member Join Date: May 1999 Posts: 5,246	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.)