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GT-40P Heads

edgeoffroad04

Full Member
Joined
Aug 12, 2004
Messages
218
All,

Starting to plan ahead to upgrade my 302 with the original '73 heads to increase performance and improve drive ability. After researching most stock and aftermarket heads, I believe the best value and price for me are the GT40P heads. I do know Ill need specific manifolds or aftermarket headers.

What is a fair price to pay for a set of take offs? Or for a set that has been cleaned up(pressure checked and gone through-springs & valves)?

Does anyone have any laying around or know of any for sale?

Thanks!
 

Timmy390

Bronco Guru
Joined
Jan 1, 2011
Messages
5,609
Loc.
Conway, AR
I got my set from a you pull it kind of place for $70 ($35 each).

Are you changing the cam from stock? The GT40 and GT40P heads have valve spring that will only support the stock can for the application they came on.

My set came off a 2001 Mountaineer. I had the springs upgraded (due to a cm swap), new valve steam seals and valves lapped. No issues......Has them frilled for 351W head bolts as well.

As I recall you can run stock Bronco manifolds if you do some grinding on them. I seem to recall that stock Explorer manifolds will work as well. I run Bronco Hut Shorties.

Tim
 

LSharpNM

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Joined
Mar 9, 2020
Messages
164
Personally I wouldn't go through the hassle of seeking out and swapping GT40P heads when there are so many affordable aftermarket options out there these days unless you get them really cheap and in good enough shape that you feel comfortable not doing any machine work on them.

As mentioned, at a minimum, you are going to need to upgrade the springs (assuming you are running or will be running a hotter cam since you are swapping heads for better performance) and invest in GT40P-specific headers (the stock GT40P manifolds are complete garbage). Add any machine shop work such as a valve job, decking them for flatness, and pressure testing/magna fluxing and cleaning, and you are looking at a fairly sizable investment. Every set of heads I have taken to the machine shop for inspection, valve job, and rebuilding has cost me $300-$500. Add another $50-$100 for valve springs and you are looking at $350-$600 on top of whatever you paid for the heads, plus you'll be stuck with GT40P-specific headers if you ever run a different set of heads in the future. You can get a set of Flotek heads for $860 ($430 each assembled https://www.summitracing.com/parts/flk-203-505/make/ford), which aren't the greatest heads in the world, but will certainly blow away some factory GT40Ps, are aluminum, and brand new. Here is a test Hot Rod magazine did a while back with budget aluminum Windsor heads, and the Floteks held their own against more expensive heads and had the best low end power: https://www.hotrod.com/articles/ccrp-1302-six-budget-ford-heads-that-work/

I haven't seen any testing done on them, but Speedmaster also makes a few sets of assembled aluminum heads right around the $850 mark (https://www.summitracing.com/parts/sdm-pce281-2108/make/ford)

My point being, I wouldn't invest too much money into GT40P heads when you can get aluminum aftermarket heads that are much better for only a little more money. If you were swapping in an entire Explorer engine, they are great, but these days I don't think it makes a whole lot of sense to put them on an engine you are trying to hot rod.
 

SC74

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Bronco Guru
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May 24, 2004
Messages
3,411
Following this thread. I just picked up a 5.0 with the p heads and will be upgrading to a set of aluminum heads. I have not decided on heads or cam yet so open to suggestions. This will be in my crawler rig, so need all the power at low RPM. I'm not trying to build a hot rod, just a basic upgrade to a stock 5.0.
 

bronkenn

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Southeast Ohio
Check out SkipWhitePerformance. They have some good prices on aluminum heads and are assembled inhouse with quality parts. Mostly Comp Cams valve springs, valves, retainers ect. Worth a look. Around 700 bucks for a pair.
 

Timmy390

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Jan 1, 2011
Messages
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Conway, AR
GT40X heads (china knock offs) have GREAT castings but bad everything else. All the Stang guys buy them bare and have them build with quality parts.

I considered it but with with P's

Tim
 

WheelHorse

Bronco Guru
Joined
Nov 22, 2004
Messages
2,491
Following this thread. I just picked up a 5.0 with the p heads and will be upgrading to a set of aluminum heads. I have not decided on heads or cam yet so open to suggestions. This will be in my crawler rig, so need all the power at low RPM. I'm not trying to build a hot rod, just a basic upgrade to a stock 5.0.

Power at low RPM...stick with long runner sefi set up with the little 302 GT40P heads.
 

LSharpNM

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Mar 9, 2020
Messages
164
Check out SkipWhitePerformance. They have some good prices on aluminum heads and are assembled inhouse with quality parts. Mostly Comp Cams valve springs, valves, retainers ect. Worth a look. Around 700 bucks for a pair.

Thanks for sharing that! According to the flow data, those should be a fair improvement over the FloTek heads, and cheaper to boot! Doing a little more research, the Promaxx heads look pretty attractive as well.
 

Bronco4x4

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Dec 21, 2009
Messages
598
Make sure you look into what headers you plan to use. I remember when buying BC Bronco headers they would not work with the gt40p heads.
 

bigmuddy

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Plenty of guys running stock 302 manifolds with the GT40P heads. They are grinding away from various plugs and using the metal plug protectors to keep the heat off the wires.
 
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OP
edgeoffroad04

edgeoffroad04

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Aug 12, 2004
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Wow Thanks everyone. Just when I think I have made up my mind on a direction I come here and I get new ideas. I'm going to look deeper into the FloTek & SkipWhite Performance. I'm not a huge hurry to buy these, but looking at the cost to pull a set of heads and have them gone over, I am getting into the same ballpark cost as a set of Aluminum heads and way more time. Admittedly I'm not an expert on engines, would a FloTek OR SWP head cause me to lose low end torque? Looking at some flow charts on line of GT-40P it looks like the lift from below 0.300 is very similar on the SWP heads. Above that the exhaust flow starts to separate itself. (Assuming this is where the gains happen with aftermarket/GT40P heads over the stock 70s heads we all have) I don't spend much time above 4k RPMs. Would I still notice a difference in the heads below 4k over stock?
 

bronkenn

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I have the SWP heads and there is plenty of low end torque. Very happy with them.
 

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LSharpNM

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Mar 9, 2020
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164
Wow Thanks everyone. Just when I think I have made up my mind on a direction I come here and I get new ideas. I'm going to look deeper into the FloTek & SkipWhite Performance. I'm not a huge hurry to buy these, but looking at the cost to pull a set of heads and have them gone over, I am getting into the same ballpark cost as a set of Aluminum heads and way more time. Admittedly I'm not an expert on engines, would a FloTek OR SWP head cause me to lose low end torque? Looking at some flow charts on line of GT-40P it looks like the lift from below 0.300 is very similar on the SWP heads. Above that the exhaust flow starts to separate itself. (Assuming this is where the gains happen with aftermarket/GT40P heads over the stock 70s heads we all have) I don't spend much time above 4k RPMs. Would I still notice a difference in the heads below 4k over stock?

Yes. Valve lift is determined by your cam, not RPM, and the cam profile remains the same regardless of operating speed. I believe most factory truck cams are in the .400-.475" lift at the valve range with factory rocker ratios. Most street-oriented aftermarket cams are in the .500-.550" range. A good set of heads will make more power everywhere, but the biggest gains will be more noticeable at higher RPM since it is when air flow demand increases that factory head castings really start to choke the engine.

Generally speaking, high lift, low duration/overlap cams that are advanced will build more torque. Basically, the cam controls your power band more than a set of heads ever will. Just don't go crazy with the intake runner volume (~160-180cc should be good for a 302) and you should have a good, torquey engine.

Here is the dyno plot before and after for a 331ci engine going from stock E7TE heads to Edelbrock Performer RPM heads with a 181cc intake port:
Graph-1-1000x5592.jpg


Here's a link to the full article if you are curious about reading more: https://www.streetmusclemag.com/tech-stories/the-pecking-order-edelbrock-ford-head-test/

As you can see, the Edelbrock heads make more power everywhere. Granted they are only making 5-10 LbFt more torque at 2,500 RPM, but that is still a gain. Also note they are making ~40 LbFt more at 4,000 RPM. Obviously the big gains are out at 6,100 RPM where the gain was ~100HP and 85 LbFt over the E7TE heads (85 HP & 38 LbFt peak to peak since the E7TE heads started losing power ~5,500 RPM). Those are gains you'll feel in everyday driving and really notice when you are goofing off!
 
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broncorckcrwlr

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Apr 16, 2004
Messages
399
Loc.
London, Ky
Check out SkipWhitePerformance. They have some good prices on aluminum heads and are assembled inhouse with quality parts. Mostly Comp Cams valve springs, valves, retainers ect. Worth a look. Around 700 bucks for a pair.

I checked out their web site and every engine that I saw was a Chevy. Not saying they don't work on Ford stuff but I'm not doing business with someone whos' is working on Chevys. A pic of a Blue Oval would add some confidence.
 

WheelHorse

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Joined
Nov 22, 2004
Messages
2,491
Are you freshening up your bottom end as well, or just bolting heads on?

IF you bolt on a tight set of heads onto a lower bottom end with 75K plus carb'd miles, you do stand a chance of running into blow by issues.
 
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edgeoffroad04

edgeoffroad04

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Aug 12, 2004
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218
Bronkenn- good to hear you are happy with the SWP- any pointers or upgrades you made to the heads before installation?

LSharpNM- Thanks for further explaining and taking me to school on lift with cams vs. RPM.

WheelHorse- bottom end is a newer short bock that is 15 years old. Less than 15k miles on it right now. My weak point is my 70s smog heads. Current running some hedman headers with a Edlebrock performer intake with a stock cam.
 

bronkenn

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Bronkenn- good to hear you are happy with the SWP- any pointers or upgrades you made to the heads before installation?

Not really, it was pretty straight up out of the box. I think if I did it over I would use a different rocker. I used the Comp aluminum rollers and they are noisy.
 
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