302 gt40's vs 351 gt40's - valve springs specs

spidermonkey · #1 (**permalink**) 05-12-2008, 10:10 AM

All I have been taking some measurements of the gt40 heads I got from Clearwater Cylinder head. I'm applying the specs from my 94 Ford service book to these gt40 heads...specifically the assembled height of the valve springs. the intake springs are within the spec (1.75-1.81 in.) however all the exhaust springs are .027 to .049 to tall. now a shim would solve this....

but I have asked CCh what spec they used when building the head. they said factory spec. yes, but WHAT spec (for which vehicle). Next they tried to tell me that my heads (F3ZE-AA) came off a mountaineer. Their invoice said gt40P, but they really sent me real gt40's. I decoded the casting code as a 93 Cobra (thanks Conaski). I do not have the specs for a 93 cobra
so I don't know if the specs are the same. (I'm disregarding the mountaineer statement and those specs cause I think the shop is wrong. the casting code says 93 cobra)

I guess the ultimate questions here is:
if the shop put springs in the head expecting it to be used on a 302 and I put it on a 5.8 will I have a problem?

I've asked for the PN of the springs they used so I can get the specs. I'd like to verify the pressure specs at specified compression levels:
Intake spring
74-82# @ 1.78 in
190-210# @ 1.20 in

Exhaust Spring
76-84# at 1.60 in
190-210# @ 1.20 in

Am I making too much out of this? I mean it's stock engine with the exeption of the blower. Do you guys question this stuff when a head comes from the shop assembled with the springs or just take it at face value that the shop did it, they must have done it right?

signed confused in Columbus, OH...

Conanski · #2 (**permalink**) 05-12-2008, 01:07 PM

Both the Cobra and Explorer/Mountaineer motors used roller cams so it's very likely the factory used the same or very similar valve springs. The Explorer/Mountaineer motors also got the GT40 heads in the early years(96-97) and the GT40p in later years(97-2k), so these heads may have indeed come from a Mountaineer. For blower applications you should actually use heavier than stock valve springs becasue the boost pressure on the back of the valves works against the springs and will result in premature valve float and loss of high rpm power. So it would be to your advantage to have springs that exceed the stock specs for spring pressure.

spidermonkey · #3 (**permalink**) 05-12-2008, 08:29 PM

Thanks Conaski. Hadn't thought about that. w/ regards to the mountaineer, wouldn't that contradict the casting code? As far as accepting the heads as is, would try accept them as is or try to validate the springs specs against the stock specs?

Thanks again. your a big help.

Regards,

Beanscoot · #4 (**permalink**) 05-13-2008, 01:07 AM

Well if you have 1.84" intake valves, at 15 psi boost that would add 40 lbs trying to open them, according to my arithmetic.

Conanski · #5 (**permalink**) 05-13-2008, 08:33 AM

Quote:

Originally Posted by spidermonkey

Thanks Conaski. Hadn't thought about that. w/ regards to the mountaineer, wouldn't that contradict the casting code?

No. The casting number only tells you what division the part was originally designed for. Ford used these parts where ever they liked.

Quote:

Originally Posted by spidermonkey

As far as accepting the heads as is, would try accept them as is or try to validate the springs specs against the stock specs?

Springs can be tested very easily by a machine shop, you could remove a pair and have them tested... or take a head to a local machine shop and have them remove and test them if you don't have spring compressor. As stated, if they turn out to be stock springs, it would be a good idea to upgrade the intake springs anyway.

spidermonkey · #6 (**permalink**) 05-14-2008, 05:42 AM

ahhhhhhh.....good to know on the casting code. I thought that that was the tell-all of where it came from. guess not. Guess I shouldn't be surprised. ford is bad about switching configurations in the middle of a given model year.

update from CCH, they faxed me the spec sheet. and they said the springs are the original springs, NOT new springs. the folks at the Ford SVT tech line said the gt40 heads from a 302 should work, spings and all, on my 351. He also said I should calc my total lift and subtract that from the installed height for the valve springs. That would give me the max compression of the valve spring and then If I really wanted I could remove the valve spring and take a reading of the spring at that max compression height.

All this too say....this assembled height on the exhaust springs is still too tall and and I'm taking the head to a recommended machine shop and spot check a few springs and get their recommendations. Hate to spend the money, but I want to be confident it is done right.

petes79f150 · #7 (**permalink**) 05-14-2008, 10:50 PM

Don't know where you're located, but (lucky me) I have a machine shop that can check spring pressures on the head. Ditto on the exhaust pressures under boost. Presumably, you're running a cam that is ground for boost (more exhuast duration). Most important in our HP builds is distance to coil bind, and believe it or not, the tighter the better. Give me a dollar and I'll tell you why.

Pete