gt40 heads

J

JT929240

New Member
Aug 21, 2008
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0
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#1
So i am almost done with putting my 302 together and i had bought some gt40 heads off a mustang forum for $400 then when my mechanic got them he said the guy had put bigger valves in without seating them so i had to bring them to a machine shop and that cost me $500 so i was not too happy with that...Then on top of all this i call a shop that just does mustangs to see how much to tune my car when its all done because i have a v-1 strim i am putting on it:doh::doh::doh: and the guy says what are you running..I tell him everything and he says oh those heads are not that good and practically no one is using them anymore...WTF..so did i just spend $900 on heads that are crap? Oh and they are the steel heads not aluminum not sure if the gt40 or gt40p all i know is that i had to buy bolts that came with sleeves to reduce the whole on the heads so maybe they were off an explorer?
 
#4
They aren't bad. They are a good budget head. Plenty of guys run them.


I helped a buddy put together a stout gt40p setup only to have a shop owner put the entire car down because of it....so we went to another shop where the guy was more than happy to help us dyno tune the car. Not everyone can afford a 10k engine.
 
#6
Well, do yup have the regular or the 40p?


The gt40 will say "gt" in the rocker valley. Stock valves are 1.84/1.54

The gt40p will say "gtp" in the rocker valley. Stock valves are 1.84/1.46

If yours have larger valves...it might help. Can you measure the valves?

Guys typically make 270-300 rwhp doing their homework with these heads. There is a slight compression bump depending on which head you have and if they are milled
 
#7
$500 at the machine shop is a hefty bill if you provided all the parts.
What exactly did they do for that much money?

IMO, the most you invest in a set of gt40 iron heads is $250 for the heads, and maybe another $250 in a valve job.

As far as guys not using them anymore, it's kinda different with a shop.
Shop owners aren't using them.
But backyard enthusiasts on a budget are.
 
#8
i think i mixed it up i had the crank balance with all the pistons and rods i think that was what he charged $500 for the heads i think were $200...but they do have bigger valves and heaver springs on them i think the guy before tried to get more power out of them but screwed it up because my mechanic said they probably ran like crap since the new valves were bigger and not seated....The other thing with these heads is it was impossible to get the right spark plug i went to autozone they gave me the wrong plugs the guy at the mustang shop said of course oh we dont carry them but gave me the part number and autozone still gave me the wrong plugs..i called cj ponyparts and the guycould not figure it out i told them they are gt40 heads and i need to run a plug one colder than oem because thats what vortech reccommends and he said i have to reaserch to find out what plug to use because they don't know so then i called summit tech line and tell the guy and he seemed like he knew what i had and what plug i needed so i ordered them i hope they fit......
 
#10
JT929240 said:
i think i mixed it up i had the crank balance with all the pistons and rods i think that was what he charged $500 for the heads i think were $200...but they do have bigger valves and heaver springs on them i think the guy before tried to get more power out of them but screwed it up because my mechanic said they probably ran like crap since the new valves were bigger and not seated....The other thing with these heads is it was impossible to get the right spark plug i went to autozone they gave me the wrong plugs the guy at the mustang shop said of course oh we dont carry them but gave me the part number and autozone still gave me the wrong plugs..i called cj ponyparts and the guycould not figure it out i told them they are gt40 heads and i need to run a plug one colder than oem because thats what vortech reccommends and he said i have to reaserch to find out what plug to use because they don't know so then i called summit tech line and tell the guy and he seemed like he knew what i had and what plug i needed so i ordered them i hope they fit......
Click to expand...


They are 93 cobra plugs.


Of course, if you could id the head we could give more info. What is written in the rocker valley?
 
#12
Cutter1024 said:
So with a mild motor, how much rwhp can you see from swapping the E7 heads for a pair of GT40p?

I found a pair that have 46k miles on them for $200. Good deal? They are local too.
Click to expand...


Depends on a lot of factors really. Stock cam? Stock intake? I guess I'd say you would gain 20 rwhp with them.....but a matched combo might give more.

There is a thread here called the 300'rwhp gt40p thread or something....where guys were shooting for 300 rwhp with these heads. It's not typical, but can be done. A lot of gt40p hci setups I have seen have been anywhere from 270-300 rwhp.

Going rate for 40ps these days is 200-250.... Cheaper if you go to the junkyard yourself .
 
#13
they are gt40 not 40p and i have an e-cam and aluminum performance rocker arms so if i can get 300 just off the motor with the v-1 strim it should bring me up to at least 400hp right? oh and i have a cobra intake on it..So what heads are the better ones gt40 or gt40p
 
#14
gt40 and gt40p heads are so close in performance, it doesn't really make a difference....the gt40's however are a lot easier to port if you go that route.

gt40 and p heads are probably hands down the most common upgrade in the mustang hobby. However, it is a budget head swap. Aluminum heads will get a good deal more hp...but who cares right? you're already committed to these heads.

expect to make maybe 275 at the wheels give or take n/a...since you have larger valves...then add the s trim...
 
#15
Let me tell you about my "budget" gt40 heads...

250 to buy them
200 to mill, valve job, valve guides, and replace some bent valves
100 for new springs
75 for gaskets

First time out bend two valves in each head because i ran at the minimum safe PV clearance you hear everyone quote. Its safe as long as your valves don't float.

200 to repair damaged valves and guides
75 for custom length pushrods
150 for new 1.6 rockers
150 for stud mount conversion kit
75 for more gaskets
Oh yeah, and as it turns out, while my heads have all the external GT40 markings, it turns out that they have the P plug angle and my old headers wouldn't work.

Save your money for new heads.

Make damn sure you check PV clearance with those heads especially if they were milled and with the larger valves.

What ratio are your rockers? If they are 1.7 you are probably in for trouble.

And check it at every cylinder.

Good luck...
 
#17
i have a new set of k\b pistons from summit racing in the block so i hope there is enough pv clearance because my mechanic has already put the motor together he just has to drop it in now..How hard will it be to check it now i would have to buy new gaskets because he would have to take the head back off to check the clearance right?
 
#18
I would hope your mechanic checked.
If not, you need a new mechanic.
No real engine builder just slaps parts together on the word of a customer, unless of course they like headaches.
 
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