• Hello there guest and Welcome to Fox Body Mustangs forum, This forum is intended to be used by enthusiasts of the Fox body Ford Mustangs (1979-1993)!
    To gain full access you must Register. Registration is free and it takes only a few moments to complete.
    Already a member? Login here then!

GT 40


New Member
Hello, I’m helping my friend with his car, it’s a 89 GT. He just picked up a set of GT 40 heads. The car already has an E303 cam in it. He also purchased Scorpion 1.7 rockers and trick flow springs. Will the cam and 1.7 rockers work together ,and if they do should I use the springs that came with the gt40 heads or put trick flow on. Thank you


Active Member
More than a handful of times I had people ask this very question.

Its not a "yes" or "no" answer from myself to anyone.
Do you know if the block deck was cut?
Do you know if the cylinder head was cut?
Also known as deck height.
Do you know what length valves you have?
What pushrod length?
Are you going to check valve geometry?
Check coil bind?

If you check all these things... You will know positively for yourself if you can or cannot.

Anyone giving you an answer from their couch is because they don't know better, and don't care because its not their engine.

Also, if you gonna run 1.7 rockers, I suggest you check spring pressures, and put the ones with highest rates on the exhaust side.
I don't understand why people put 1.7's when the cam wasnt designed for it. No one considers the ramp rates and how that affects spring control of the rockers.
Then there's the heat involved.

Good luck, hope the goodies you have put some grunt in the engine!


Well-Known Member
I'm from the camp that says never use old stock springs for a performance application. The explorer cam was pretty low lift, if I'm not mistaken. Plus, the springs are old and worn, at best. A new set matched to the cam (with the rocker geometry factored in) is cheap insurance.

I ran a B303 with 1.7 rockers in my 88gt. Block and rotating assembly was stock, but I was using some heavily ported and modified factory '69 casting heads. I used new springs spec'd for this application and valve clearance was checked. While I normally wouldn't suggest this build, I literally had everything but the valve springs already lying around, so I put them to use. As luck would have it, that thing was an absolute terror, for a pile of spare parts. My buddy now owns it, but he over-revved doing a smoke show and broke a valve spring. It didn't hurt anything... didn't even drop the valve. I have the heads sitting on a shelf now. He went to a set of aluminum heads.

But 347HO is correct. There are a lot of factors to consider here. For example, is the engine stock? If it's been replaced, what pistons were used? Do they have valve reliefs? If I were a betting man, I would say he'll be fine. They've been tossing E cams and 1.7 rockers in 302's for years. The problem is that they've also been swapping rotating assemblies too lol!