GT40/GT40P head questions, worth it with my setup?

Fett · Jun 7, 2006

I have a bunch of questions regarding GT40/GT40P heads. I currently have a stock block, e-cam, 1.7 rockers, stock heads that have been mildly ported….basically just gasket matched and cleaned up. Edelbrock Performer upper and lower, 24lb injectors, Ford Racing headers. UPR x-pipe, throttle body and MAFS.

I was getting ready to add on the rest of the stuff I collected, electric fan, new distributor, and MSD 6AL/coil. The only thing I am really missing is a decent set of heads. I was trying to find a set of good, used heads…but currently that is not in the cards. Basically because I lack the extra funds to buy heads. I read a lot of threads talking about GT40 and GT40P heads. I think the info I read confused me more.

Basically with my setup, would there be any real advantage for going with either gt40 gt40p heads? If so, which would be better to go with? Should they also be cleaned up/ported, or just slap them on? I ask because we have a few Explorer 5.0 motors laying around, from different years. I am not sure which heads are on them, the gt40s or the gt40Ps.

Should I just stick to the heads I have, or would there be an advantage for going with Explorer heads?

Strype · Jun 7, 2006

GT40P's on the Explorer... they're better

85_SS_302_Coupe · Jun 7, 2006

Try to get the P's but be aware that your headers may not work with them due to the angle of the spark plug. The advantage is that right now your heads are the bottle neck that everything is going through....get bigger heads and the rest of the stuff is going to get to work to it's full potential, or at least a much higher potential than the heads you're running now.

A decently built bolt-on GT40P engine can run 12.50s on slicks. That's with stock bottom end and no power adders.

Fett · Jun 7, 2006

How can you be sure if they are GT40P or just GT40? The engines are literally just sitting on the ground.

As far as my headers, I heard you can get around needing new headers by modifying the plug boots, is that true?

Should a set of these heads be decked down at all, or just resurfaced?

Are stock pushrods/valves/springs/ect all ok to use with those heads and the rest of my set up?

Sorry for asking such a barrage of questions, I just don't want to walk into any suprises.

Oh, and what is the main difference between gt40s and gt40ps....performance wise? Two of the engines are 96, so those are GT40 heads. If there is that much of a difference between the two, I will try to find gt40ps. But if the difference between the p and the non-p heads is not that huge, then I might just stick with the non-p heads and not worry about the wire issues.

Either way, this would be a much better way to go than keeping my stockers, right?

fidstang · Jun 7, 2006

Tri-state cylinder heads has some with larger valves for around 500.00. With some basic port matching the P heads they have will out perform your port matched E7's. Just don't forget to add in all the gaskets, bolts and extra you may need to see if it's worth it.

orangecapri · Jun 7, 2006

Yes you can use regular headers most of the time. You may have to take them off to change the plugs or modify a spark plug socket, but they will work if you have 90* spark plug boot ends. Im running standard chrome bbk shorties right now and have no problems.

Fett · Jun 7, 2006

fidstang said:
Tri-state cylinder heads has some with larger valves for around 500.00. With some basic port matching the P heads they have will out perform your port matched E7's. Just don't forget to add in all the gaskets, bolts and extra you may need to see if it's worth it.

Yea, but the ones that are available to me are free. So it really is a matter of deciding which way to go. I am thinking that I might have to settle for some gt40 non-p heads, so it boils down to deciding between the set of heads I have now (gasket matched ported) e7 heads, or gt40 non-p heads that I will also gasket match.

If there isn't that much of a difference between non-p heads and stock, I will just wait.

Plus I don't know if those springs are good for my setup. Springs don't cost that much, so gaskets, valve job, and possibly springs would be worth it IF the non-p heads would complete the rest of my set up better than my e7 heads.

85_SS_302_Coupe · Jun 7, 2006

They actually say GT40 or GT40P in raised letter on the head under the valve covers, but also the regular GT40s have three bars on the front of the heads and the Ps have 4 bars.

GT40s are the same heads as were on the '93 Cobra....they're definately badass heads for a budget so if you don't have some Ps don't worry too much about it. I've seen nearly identical power numbers from both heads. In fact, my friend ran 4 tenths faster with his regular GTs than my buddy's GT40P car, and that car had a cam verses my friend's stock cam. It all comes down to combo.

bubba-dough · Jun 7, 2006

The GT40P's would be the better ones to get performance wise. Don't worry about the headers....you said you have Ford Racing headers. Those are made to clear the GT40P's. As far as using stock rods and such, that is fine. And look at it this way...the GT40P are better than the GT40 which are better than the E7 (all stock and untouched). If you can get either GT40 heads, for free that is, and do the same to them as you would the E7's you are still gonna have a better head than the E7's with the same work..

Fett · Jun 7, 2006

I am going to check the heads now and see which ones they really are.

Which springs should I use, the ones IN the head or my stock heads off my e7? Or should I get a set of springs anyway?

85_SS_302_Coupe · Jun 7, 2006

bubba-dough said:
The GT40P's would be the better ones to get performance wise. Don't worry about the headers....you said you have Ford Racing headers. Those are made to clear the GT40P's. As far as using stock rods and such, that is fine. And look at it this way...the GT40P are better than the GT40 which are better than the E7 (all stock and untouched). If you can get either GT40 heads, for free that is, and do the same to them as you would the E7's you are still gonna have a better head than the E7's with the same work..

GT40/40P castings are identical with the exception of the spark plug location/angle to improve cylinder combustion and emissions. We're talking nickles and dimes as far as power difference between the two.

fidstang · Jun 7, 2006

I perfer the non-P's for boosted applications. I heard the smaller exhaust valve on the p's hurt the flow on boosted apps. Not sure if it's true or not.

95GTAODE · Jun 7, 2006

The P's also have a smaller 58cc chamber, compared to the 64cc's on the standard -40 head.

Fett · Jun 7, 2006

Ok, so if I am not planning on going with any power adder (nitrous, SC, turbo) then the GT40P heads are the way to go due to compression. Where as if I DID go with a power adder, then GT40 would be the way to go....right?

That said, what if I went with GT40 non-P heads and decked them .03 to raise compression?

Either way, stock springs will not be a problem with either head plus 1.7 rockers and an e-cam? I just want to be 100% sure on the springs issue...I hear a lot of people run into valve float issues with stock springs.

JBeezy53 · Jun 7, 2006

You can't go wrong with either set. I went back and forth for a while to and ended going with the best deal I found. I got a set of P heads. I have been real busy so I haven't been able to install them yet but I am putting new springs on before I install them.

95GTAODE · Jun 7, 2006

With 1.7's and an E cam, upgrading the springs on either head is just about mandatory.

TFS has a good, affordable spring kit for late Ford heads.

I went with the Edelbrock RPM springs that matched my cam on my P's.

Tonys96Cobra · Jun 7, 2006

E7's flow about 150/120 @.500 and Reg GT40's flow 190/150 @.500 so thery are definitely an upgrade. P heads flow slightly more on both sides even with the smaller exhaust valve.

Fett · Jun 7, 2006

I am searching for springs now. My problem is that I am still learning about all of this. I can build anything....as long as someone hands me the peices. I am trying to learn as much as I can, so this all makes sense. I am still learing about cam lift and duration, and how it relates to the flow and spring rate...ect ect. So numbers confuse me because I don't know what everything means yet and how they will all relate to one another.

Springs for instance, you go to jegs or summit and look at springs...they are all listed by diameter, rate, blah blah blah. Of course it all being Greek to me...I get lost rather quickly. Which is why I am asking a thousand questions. I am hoping that while today I am the annoying guy asking a ton of stupid questions...tomorrow I will be "knowledged" in it all.

So please bear with me as I ask all the standard questions. And thank you all for your help and input.

Woodrow · Jun 7, 2006

If you want to lower the compression just get cometic gaskets. The gt40p's love the juice.

I 2nd the tfs spring, good and affordable. DO a search on here or corral on of the recent threads about gt-40 & p heads has the part number in it.

legalize420 · Jun 7, 2006

take the heads to the machine shop. i paid $180 to clean, resurface, and get a valve job. im still on stock springs but next time i pull my heads im changing them. im going with the trickflow kit from summit. just search for 302 valve springs and you should find it.

GT40/GT40P head questions, worth it with my setup?

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