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Discussion Starter · #1 · (Edited)
Need a little guidance on Valve Spring Selection, setting up a new set of heads.

Correct me if I am wrong but the OE Springs are about 70 lbs on the seat.

Ferrea Stock diameter valves. Cams are custom, .472 lift and not much more than stock duration since I want to retain the ability to pass CA Smog (it does).

At 6300 rpm and 25 psi boost, any guesses as to what seat pressure I will need? What is the consensus on the Comp Cams 26123 springs, any good?
 

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You will have to measure the backside of your valve to get your answer but this is how the math goes. Take the area of the backside of your valve (diameter^2 multiply it by Pi/4) and multiply it by your manifold pressure to find out how much spring pressure is required to overcome boost trying to lift the valve off the seat.

Let's say your intake valve backside that is exposed to manifold pressure is 26mm. To get the diameter in inches divide by 25.4 and you discover you have a diameter of 1.02". Square the diameter and multiply by pi/4 and you get 0.82 square inches.

At 25 psi you have 25*0.82 or ~21 lbs of force from manifold pressure trying to open your intake valve which the valve spring must overcome to keep the valve seated. With springs that seat at 70lbs that means you only have 49lbs of spring pressure during engine operation that is holding the valve shut.

I would look for something with a seat pressure around 90lbs to be on the safe side. I would also look for springs that have a spring rate of more than 300lbs/in. They will give you good valve control at elevated engine speed.

Ed
 

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Discussion Starter · #3 ·
Ed,

Thanks for your response. I had already made the calculation and come up with a force of 36lbs. I guess what I was really looking for is what spring pressure it takes, with stock cams, to run 25 lbs boost.

The way I see it, I am going to need a spring that gives me at least 100 lbs on the seat, the Comp.Cams 26123 springs aren't going to do it, the max I will get from them, at my installed heigth is 88 lbs.


Any suggestions on a spring that is going to work on a DD and not cause self destruction? Am I correct with my ~70 lbs as being the stock spring pressure on a Cobra?

Mike
 

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I went with the Crower X2 springs. They have a slightly higher seat pressure then the non X2 springs and they are a little cheaper as well. Are you going to be using stock install height? Or do you plan to shim them? The Crower springs require the use of their spring retainers so keep that in mind. I think the only spring that uses a stock retainer are the Livernois springs. The Crower X2's offer about 98lbs on the seat at the stock 1.470 height, they're 103lbs at 1.420.
 

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Mike,

Here is a spreadsheet of springs that I put together back in 2007. There are couple of new offerings since then but this should get you started. BTW one of the companies coming up with a new offering I think was Manley another was Crower and I am sure there were others also so you ought to check out their websites just to be certain.

Ed
 

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I'm using the livernois motorsport springs. They are actually overkill for me, with Ford GT cams, and probably 12-15lbs boost.
Note: nice alternative as they did not require purchase of aftermarket retainers (or any other parts), or machining of the spring pockets.
 

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Just a heads up... they probably aren't enough for most of your setups, but if anyone needs any, I've got a brand new set of springs off a set of FGT heads that I bought new straight from Ford. I'll sell them right....
 

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Discussion Starter · #9 ·
Mike,

Here is a spreadsheet of springs that I put together back in 2007. There are couple of new offerings since then but this should get you started. BTW one of the companies coming up with a new offering I think was Manley another was Crower and I am sure there were others also so you ought to check out their websites just to be certain.

Ed
Thanks for the spreadsheet, outstanding.

I did numerous google searches and only came up with Manley, Comp Cams, Crower, PAC and FRPP. FRPP gives no data on thir springs and I didn't find anything suitable on the PAC site.

I should be able to find something workable on your list, I'm only looking for 100# @ 1.470.
 
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