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Old 11-16-2017, 11:06 PM
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GT 40 heads

I got a pair of GT40 heads out of a 97 mountaineer.

I'm going to put them on my 302 in 67 mustang.

I was thinking I should get the heads resurfaced to get a higher compression ratio?

What is a good ratio to use where I can have as much compression as possible on regular gas?

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Old 11-17-2017, 06:57 AM
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"as much compression as possible" also involves your camshaft and pistons... So, what are they?
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Old 11-17-2017, 08:00 AM
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Quote:
Originally Posted by AutoGear View Post
"as much compression as possible" also involves your camshaft and pistons... So, what are they?
X2!

To the OP, design philosophy between 1967 and today has changed to meet current unleaded fuels with top octane being what regular fuel octane was in 1967. As much as anything this has along with improved combustion chambers has also brought a change in cam design to less lobe ramp, shorter duration with faster lift rates, and much wider LSAs that reflect less overlap. A critical point is where the intake valve seats in crank degrees.

So knowing what Pistons are in the engine and what cam are important factors in determining how much compression can be tolerated with modern fuels.

Bogie
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Old 11-17-2017, 09:26 AM
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The GT40 heads are basically a Vortec chamber, right Bogie, et al?
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Old 11-17-2017, 11:21 AM
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Quote:
Originally Posted by AutoGear View Post
The GT40 heads are basically a Vortec chamber, right Bogie, et al?
Yep. Chrysler calls their's Magnum. These chambers are common all over the aftermarket as well. These are applications of the research done before WWII into chamber designs by Sir Harry Ricardo in England and Charles Fayette Taylor here in the U.S. and I'm sure there are other researchers around the developed world at that time who arrived at the same conclusions about inline valve wedge chambers. Ford actually tried these chambers out with the Lincoln big and Ford small Y blocks using them from 1952 to 1955 then they simpled the shapes probably, my guess is, to avoid paying royalty fees to the inventors. The picture is a Y block Ford Chamber while it lacks the beak of contemporary chambers you can certainly see the contours on the spark plug side. The later chambers of the Y-Block just make this a bath tub similar to the SBC's and SBF's early chambers.



Bogie
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Old 11-18-2017, 07:59 PM
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I dont know what cam is in there.

6 years ago I put in a crane cam but I don't remember what it is now.

It has flat top pistons.
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Old 11-18-2017, 08:08 PM
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I'm thinking I might just leave the heads the way they are and just bolt them on.

Im not sure what rocker arm ratio to use. I was thinking I could use the stock ones on the gt 40 heads. Then use a dial indicator and see how much lift the cam has for intake and exhaust. Then look up the ratio of the stock rocker arms and calculate the valve lift. And see if that is too much for a 302? Will this work? Or do i need to use clay or something
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Old 11-19-2017, 01:41 AM
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Quote:
Originally Posted by RobbyDD View Post
I got a pair of GT40 heads out of a 97 mountaineer.

I'm going to put them on my 302 in 67 mustang.

I was thinking I should get the heads resurfaced to get a higher compression ratio?

What is a good ratio to use where I can have as much compression as possible on regular gas?
1997-2001 Mountaineer 5.0's used the GT40P cylinder heads if you have headers this can cause an issue with the spark plugs not clearing the tubes,the earlier GT40's are OK. Both the GT40's and GT40P's valve springs will not support a higher lift cam than stock so you need to address that also.
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Old 11-19-2017, 01:44 AM
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Quote:
Originally Posted by RobbyDD View Post
I'm thinking I might just leave the heads the way they are and just bolt them on.

Im not sure what rocker arm ratio to use. I was thinking I could use the stock ones on the gt 40 heads. Then use a dial indicator and see how much lift the cam has for intake and exhaust. Then look up the ratio of the stock rocker arms and calculate the valve lift. And see if that is too much for a 302? Will this work? Or do i need to use clay or something
The problem isn't one of maximum lift but rather too much lift on the valve as the piston closes at TDC. To do a computation you would need to know the lift in crankshaft degrees and the piston position in the bore at those degrees, you gotta know a lot about the cam timing and lift rates and be able to due a lot of trigonometry to find where the piston is in the bore to crank degrees, this is not linear because as the crank turns the apparent length of the stroke changes and the connecting rod whose length is important is opening and closing different forms of triangles. This makes pulling a head and sticking a blob of clay on a piston then reassembling everything then turning the crank around, then taking the head off again to measure the clay look pretty simple.

Bogie
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Old 11-19-2017, 07:35 AM
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Quote:
Originally Posted by RobbyDD View Post
I'm thinking I might just leave the heads the way they are and just bolt them on.

Im not sure what rocker arm ratio to use. I was thinking I could use the stock ones on the gt 40 heads. Then use a dial indicator and see how much lift the cam has for intake and exhaust. Then look up the ratio of the stock rocker arms and calculate the valve lift. And see if that is too much for a 302? Will this work? Or do i need to use clay or something
You're in need of a cam degree kit, either bought or homemade. There is no better time than the present to learn. Also, aspects of degreeing a cam are a much easier task with the heads removed.

JEGS Precision Cam Degree Wheel Kit | JEGS

Putting this together and experiencing some piston to valve contact, broken valve train components due to coil bind or poor rocker geometry makes degreeing the cam seem like a function that cannot be excluded.
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Old 11-19-2017, 10:39 AM
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On any of my engine builds i use the clay. never mind do not argue with the old guy just do it. Only takes one blown motor to cure you...

A fellow can get by if he is just doing a valve job on a stock motor..

Sam
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Old 03-19-2018, 04:16 PM
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97 was a split year. Lates had P heads with 4 bars lines cast on the end. Need different headers to clear plugs.

Big combustion chambers. @62-65 cc nominal. Compression?

The 68 302 4bbl had 54cc heads but a slightly dished piston. There 3 different dishes through the years and heads up to 65 cc on the smoggers.

Assuming stock lift cams, Flattops with valve reliefs with stock valves will clear ok unless you mill the heads, then be sure to clay them.

Milling the heads' deck requires also milling the head's intake surface, or .... you can ruin the intake manifold by milling it and making it unuseable on any other engine.

Sometimes you can squeeze by using extra thin intake gaskets to make up the distance shrinkage of not milling the head intake surface.

Stock Mountaineer rockers work fine with stock 302 pushrods... All this assuming youre sticking to a low lift - .478 cam.

You might expect 25 hp increase minus any compression loss.
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Old 03-20-2018, 09:52 AM
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What HP engine was your 302 when new?

What RPMs range does the Crane cam pull in? 1000 - 5000? Up to 5500? Up to 6000? Up to 6500? Is it a solid or hydraulic cam?

GT40/GT40P heads are better than other 1970's heads... don't know if better than 1960's heads... there are instructions online on how to distinguish GT40 from GT40P heads...
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Old 03-20-2018, 10:00 AM
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Quote:
Originally Posted by RobbyDD View Post
I dont know what cam is in there.
6 years ago I put in a crane cam but I don't remember what it is now.
It has flat top pistons.
A lot of people tell us they have flat top pistons, then submit a picture and they have a large diameter shallow dish with 4 valve reliefs, that's why we always question/double check that statement... sorry... Has the engine been rebuilt? Pistons replaced?
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Old 03-20-2018, 10:08 AM
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See Post #12 ..... 4 lines is the P heads.... therefore 3 lines are the plain gt40.

They have hard seats but around 63 cc chambers. 302 heads with the fat spark plugs are smaller.

302 heads with the 5.0 type rocker arms starting in 74 had small spark plugs and big chambers. The same head was used on the 351W.
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