defiant1

Okay, based on the cam I am going to get I need better than stock valve springs.

The stock spring height is 1.670" but I can't find a valve spring that maintains the stock spring height and has at least 100 lbs of seat pressure and a open pressure of at least 275 lbs.

So can I choose a spring that is a little longer to achieve the seat pressure and open pressure I am looking for?

d1

Run to Rund

See what your installed height actually is. It is common for it to be over 1.7" after a valve job or two. I have several sets of dual springs that give around 120-130 seat and 300-330 open depending on installed height and lift.

defiant1

I am in the process of having a valve job done (bigger intake valves and stock exhaust valves with hardened seats).

Once the new valves are installed how/what do I measure to ensure the correct spring length? Or am I approaching this all wrong?

Run to Rund

Measure the distance from the retainer surface for the spring to the spring seat in the head. That is installed height. Subtract the lift at your rocker ratio and that is the open height. For example, after a valve job your installed height is 1.70" and the lift at the valve is .475". Your open height is then 1.7 - .475 = 1.225. Get springs with appropriate pressures at those lengths (installed heights).

defiant1

How critical is I.D. and O.D. when choosing the springs? I found a set of springs with the correct seat pressures for the cam but the outer diameter is 1.440 vs. 1.437 and inner diameter is 1.041 vs. 1.039.

Or do the spring retainers accommodate for this?

d1

Rickman48

There are spring shims available to make up differences in spring heights - a flat washer in .010 to .050 thicknesses.
I'd be leery of a machine shop that didn't know of them!
As far as the retainer - .015 on a side shoudn't make a difference, and if you have the heads machined for PC seals, they should accept dual springs.
Are the guides in good shape? Some valves are available with oversize stems, just for that reason, but most shops won't tell you about them, "you need new guides", and charge accordingly.
When I was doing heads, I was told to use a .020 shim on all stock valve jobs, and "set" the spring height on all hi-po jobs - measure every valve to get 110-120 on the seat!

cutlassefi

That should be for a typical flat tappet hydraulic. But you still need to know spring rates, could still have too much or too little when opened.
1.440 vs 1.437 is .003 or one strand of your hair, not an issue.
Don't need dual springs for this application imo.

tonycpe

It was hard for me to get the proper spring rates and stay away from coil bind with a .560 lift cam on # 5 heads
Had to go with longer big block valves.
You may want to look into plus .050 10 degree retainers and locks .
I got my parts from comp cams.

Run to Rund

If you add .050" height with special split locks or retainers, they may not clear the stock rockers. I add only chrome moly hardened shims which are also made as locators, either internal or external. Regular shims will get chewed up, sending metal where you don't want it. The Isky 507STA retainer is about .070" more installed height and does work fine with standard or Isky 1132 locks.