gt40p head

butch botch · Nov 12, 2022

Hi Guys Butch here from Canada--I am a novice at this I have a couple of questions---I am doing a head swap on my all original 1975 302 engine. I have accomplished a 2 bbl carb & manifold swap to a matching set of Edelbrock aluminum 4 bbl intake. Now I am about to do a head swap to a set of gt40p heads. The heads have been planed 12 thou to make them true--I am installing a set of headers new lifters and a new 2,5 inch exhaust what kind of hp and compression increase in general terms will I be looking at after all is complete--thanks

extra_stout · Nov 13, 2022

Hello to Canada and welcome,
I think you mean that the heads where planed 1.25mm, which is still a lot. My GT40p heads where planed 0.5mm.
Because the compression depends on the used pistons it is hard to tell, what you compression ratio will be.
I have a 2001 explorer block, which has a stock compression of around 9.0. The compression should be around 9.5 with the milled heads in my case, because rotating assembly and pistons are stock.

Enzio · Nov 13, 2022

Everyone will want to see PICTURES!
Welcome.

2Blue2 · Nov 13, 2022

butch botch said:
I am doing a head swap on my all original 1975 302

First welcome aboard...

Picture of the 48 panel would be fun!
75s were a dished piston lower compression engine usually so any bump would be an improvement.

Make sure to check piston to valve clearance with the new head and all that milling...

butch botch · Nov 13, 2022

LILCBRA · Nov 13, 2022

extra_stout said:
Hello to Canada and welcome,
I think you mean that the heads where planed 1.25mm, which is still a lot. My GT40p heads where planed 0.5mm.
Because the compression depends on the used pistons it is hard to tell, what you compression ratio will be.
I have a 2001 explorer block, which has a stock compression of around 9.0. The compression should be around 9.5 with the milled heads in my case, because rotating assembly and pistons are stock.

The way I read the OP's post is that the heads were planed .012 inch. In metric terms, that would be .3048 mm - so less than what you've had done. To give people a visual, that would be about the thickness of 4 pieces of notebook paper.

To the OP - the original engine specs said that it only had about 8:1 compression with 58 cc heads. The GT40p heads are also ~58cc heads, so there will really be no bump in compression from the heads. As for horsepower numbers, that's going to be hard to tell really. IIRC, GT40 heads are only really good for 20-30hp over E7 heads, and E7 heads are a little better than their predecessors. So, you might go from the stock horsepower number of 140ish to 160-180(?) depending on other variables. Again, this is all a guess.

You mentioned new lifters - is there also a new cam in the works?

extra_stout · Nov 14, 2022

LILCBRA said:
The way I read the OP's post is that the heads were planed .012 inch. In metric terms, that would be .3048 mm - so less than what you've had done. To give people a visual, that would be about the thickness of 4 pieces of notebook paper.

OP edited his post
With that number you do not need to consider the change in compression. When I adjusted lifter preload I needed shims for nearly all rockers even if I kept the whole valve train as it was from factory. So keep in mind to double check that (beside pushrod length). Or do you plan to convert to studs?

butch botch · Dec 4, 2022

Good Morning to all in the previous thread I was incorrect in the amount of skin removed from the heads --after talking to the machinist it seems that aprox 10 thou was removed to make the heads flat --now the question is will I need to change the pushrods-- I am using the original non adjstable pushrods that came with the 1975 302 engine and new hydraulic lifters set for the 75 engine block .--thanks Botcho

extra_stout · Dec 4, 2022

As far as I understand you are swapping from 75 original heads to gt40p heads?! If so I think you need a new push rod length for sure. which rockers will you use? Pedestal mounted like the GT40p heads are from factory, or do you convert to stud mounted rockers?

LILCBRA · Dec 6, 2022

I'd definitely suggest that you invest in an adjustable pushrod and double check the valve train geometry to make sure.

Something like this: https://www.summitracing.com/parts/tfs-9000

Noobz347 · Dec 6, 2022

If you really want to get crazy, convert to roller.

https://www.summitracing.com/parts/hrs-91169-2/make/ford

gt40p head

butch botch

Member

extra_stout

Enzio

Dang it. I was hoping mine would get 3 more inches

2Blue2

will be trying this sex one when I can find it

butch botch

Member

LILCBRA

I wish I didn't have all of these balls in the air

extra_stout

butch botch

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extra_stout

LILCBRA

I wish I didn't have all of these balls in the air

Noobz347

Stangnet Facilities Maint Tech... Er... Janitor

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gt40p head

Member

Dang it. I was hoping mine would get 3 more inches

will be trying this sex one when I can find it

Member

I wish I didn't have all of these balls in the air

Member

I wish I didn't have all of these balls in the air

Stangnet Facilities Maint Tech... Er... Janitor

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