GT40 heads and valve springs

[wbdevil67]

Hi guys
I am installing GT40 heads on a non-roller 80s block with a hydraulic lifters and flat tappet cam. I am using the stamped steel rocker arms that came on the GT40 heads.
My question is what push rod will work and do I have to change the valve springs?

Thanks

 

[Timmy390]

Springs should be matched with the cam you plan to run.

Pushrods should always be measured because of all the variables (block and head milling, gasket thickness, lifters and rockers)

I got my pushrod checker and my springs for the GT40P's I'm running here:
https://www.alexsparts.com/

Tim

 

[73azbronco]

What Timmy said, you are mixing two most likely compatible parts, but need to verify as the pushrods might be different length, however I doubt it.

 

[blubuckaroo]

Always have the spring rate and tension checked, even if the springs come with the cam kit.
You'd be surprised how often they need shimming to get them right.
There are just too many variables to sell something that doesn't need checking.

Take the heads along with the cam card to a good machine shop. They'll set them up.

 

[sykanr0ng]

The valve springs WILL need replaced.
Ford put springs that were just adequate for the cam in the engine which is a very mild cam and no more than that.

 

[Timmy390]

I know the GT40P's springs are junk.....Just good enough for the Stock Explorer cam only....

Don't know much about the GT40's

Tim

 

[DJs74]

Hi guys
I am installing GT40 heads on a non-roller 80s block with a hydraulic lifters and flat tappet cam. I am using the stamped steel rocker arms that came on the GT40 heads.
My question is what push rod will work and do I have to change the valve springs?

Thanks

Yes, what they all said.

New build / new camshaft or are you replacing the cylinder heads on an existing motor with established camshaft and build sheet?

If you know the camshaft P/N or specs, you can back into the springs and pick the right ones to match your camshaft... that is not only important but a must, IMO. The camshaft and cylinder heads are the heart of your motor and where you get your performance. Not that pistons, rods and intakes are not important...
If you have a good local shop, they can set the springs up for you by checking your seat and open pressures per the manufactures specifications.

Pushrods... Ø5/16, thru hole and length 'X' depending on your setup. The ones you had in it originally could be a starting point but if you are ordering parts, pick up an adjustable pushrod length checking tool and then you'll know within thousandths of inches what you need for the length. Probably something around 6.75" to 6.95" if I'm guessing and I am just guessing.


DJs74

 

[KyleQ]

Replace the springs regardless - I left the stockers in mine and I got lots, and I means LOTS of valve float after 5700ish RPM.

 

[spap]

I would check the piston the valve clearance too. Some of the pistons do not have the valve reliefs cut into them like an HO motor and might cause a problem. I have a 90 s non HO motor and can not run the gt40 s heads because the piston in the block are basically flat top and would hit because no valve reliefs cut into the piston and the valves are bigger in the gt40 heads
Some one here will know a lot more than me, but something to check

 

[latrucker]

It's good to check PTV clearance but unless you running a came with some overlap it really shouldn't be an issue. As for measuring pushrod length, search for "Scott Foxwell pushrod length" on YouTube. He shows you how to use the "half lift method" it is very simple and is right on Everytime. He is a well respected engine builder and worth listening to. Just my .02

 

[wbdevil67]

Thanks all for the info
I am running a new edelbrock performer 2122 flat tapped with new hydraulic lifter that came with the cam. so I do have the specs should I go with the springs that edelbrock has to match that cam #5922 (for valve rotators) or go with another spring
Once again thanks for the help

 

[Timmy390]

I would run the springs E-brock recommends with their package.

Tim

 

[DJs74]

Thanks all for the info
I am running a new edelbrock performer 2122 flat tapped with new hydraulic lifter that came with the cam. so I do have the specs should I go with the springs that edelbrock has to match that cam #5922 (for valve rotators) or go with another spring
Once again thanks for the help

You are pretty safe going with the camshaft manufacturers spring recommendation but you do not have to. I like Howards, Comp and Lunati springs depending on the application
The things to look at are:
* installed height (valve on seat)
* seat pressure (lbs.)
* coil bind height
* open height (max lift)
* open pressure (lbs.)

Also beware of the spring OD & ID to make sure they fit your cylinder head spring pocket. If you match these areas, you can use any spring manufacturer you like

DJs74

 

[WheelHorse]

I run E7's with the stock rockers. I did the screw in kit so I could keep the rockers adjustable. I went with a pushrod length that gave me a nice pattern on the valve. The stock springs checked out with the mild Edel cam.

If you plan on revving to 6G and have the intake and carb to support it, I would upgrade the springs.

 

[blubuckaroo]

Even the recommended springs should be checked by a machine shop. The rate and tension are affected by the valve length, seat depth, and valve cap dimensions.
There's no way the recommended springs can be guaranteed to be correct right out of the box.