This is for the 92 GTA in the sig.

Over the winter i'm looking to upgrade the valve springs. I have hit valve float accidentally because I forgot to change the RPM limiter in the prom. I got lucky that nothing was actually damaged due to float.

I make peak horsepower at 6500 rpm.

Due to all the other mods on the engine, is valve springs all i'm going to need to spin that high?

 

We would need to know the mass of the valves, retainers & locks, push rods, the lifters (if they are not stock), and reciprocating mass of the rockers (effective mass about the moment center). We can compute the approximate peak acceleration rate of the valve train based upon the cam specs you provide, and the result will be an approximation of the peak kinetic force of the valve train placed upon the spring, not counting harmonics and friction.

After a crude estimate here, you can send that same data back to Comp and they can suggest a suitable spring standing pressure and rate.

 

Wow! Not so simple is it.
I have everything that came stock with the AFR 195 Eliminators
Stainless rockers
Stock lifters.
And the cam specs in the sig.

I take it i'm going to need to get more specific for comp?

 

Manley valve in the heads? If so, we can find the mass (or something close) easily. We can presume the retainers and locks,and assume the push rods and lifters if you don't have part numbers.

 

Just says AFR 8mm LS1 Style standard length 2.05 intake &
AFR 8mm LS1 Style standard length 1.6 exhaust

I'm using the stock lifters and the following pushrods:
TFS-21407200 Trick Flow hardened pushrods 5/16" 7.2" length chromemoly

 

O.K. I've done the crude geometry.

Intake Valve Rate at Peak RPM - 7.109 F/S
Exhaust Valve Rate at Peak RPM - 6.995 F/S
Intake Valvetrain Rate at Peak RPM - 4.740 F/S
Exhaust Valvetrain Rate at Peak RPM - 4.663 F/S

Even though the exhaust side has more lift, the longer duration drops the rate below that of the intake side.

If you have some kinetics formulas, you can apply the Intake Valve rate (inches per second peak) to the mass of the valve, retainer, lock, and half the rocker. That will be one-half of the force calculation.

Apply the Intake Valvetrain rate to the mass of the lifter, push rod, and half the mass of the rocker. Add that result (in pounds) to the previous result, and you should know the peak pressure required to manage the valves.

If you don't have any calcs at hand, you can use this formula:

KE (Lb) = 0.5 * Mass (LBS) * Velocity (Ft/S²)

Find a spring with the correct initial pressure and correct rate to meet the requirement at peak lift (peak spring compression) and you will have an adequate spring for 6,500 RPM. Installing more spring than necessary is just a waste of horsepower and will result in more heat.

Do the same for the exhaust side and select that spring accordingly.

As an example, a typical Manley SS intake valve at 105 grams will require 34.39 pounds of spring pressure alone at 6,500 RPM. Add to that half of the mass of the spring itself, the mass of the keeper, effective rocker mass, push rod, etcetera, and you can easily see a need for 300 pound springs in higher RPM applications.

 

Can aluminum heads with screw in valve studs support that kind of seat pressure?????

 

I know guys running upwards of 600lbs open pressure on heads like that.

 

Ah yes the gargantuanly high open pressures....I remember going through that.

What kind of springs are on there now? And did Comp recommend a spring to begin with?

 

The springs that are on there now are AFR's stock Eliminator springs. All i've been able to find out about them are that they're "LS1 style".
I never talked to comp about springs. When I originally built the engine it was still a 350. I had peak hp ~5900 rpm. No problem. But when I melted a piston I went to a 383 which ended up extending my rpm range upwards. Now i'm trying to make that last 80hp useable.
How much of a RPM safety feature should I also build into it? I will be programming my RPM cutout to below the springs limit.

 

your springs are AFR 1.29" dual springs, the 8017's they call them. 130-135 lbs on the seat and 360 or something like that open.

Call AFR and tell them you want their competition 1.27" valve spring. Part number 8019. Its their upgrade high pressure spring for their 180/195 comp ported heads

Coil Bind 1.080
Max Rec. lift .650 Net (still .060 from coil bind @ 1.790)
Seat pressure 155 lbs. @ 1.810 (standard installed height from AFR)
Spring Rate 428 lbs. per inch
Open pressure (@ .600 lift) 412 lbs.



Take that spring and install it at a 1.775 or so installed height and it should handle that cam. That will give you 165-170 lbs on the seat and well over 400 open.


This is the same spring setup i'm using on my 383 that has seen 6800 rpm with no apparent problems, even tho its done making power by 6300

And are you sure its making peak at 6500? that seems awfully high for that setup in your sig.

 

"Peak" according to DD2K.
SOTP it's still pulling at those rpms like it's in first gear.

I never made it to the dyno this year. Still gonna try.

What's the general consensus on different springs rates between intake and exhaust?

 

if your intake ramps are more aggressive then run more pressure on the intake side. I run 170 on intake, 166 on the exhaust just because thats how the installed height came out.

 

For my 406, I run seperate springs on the intake an exhaust. Probably a little different, though.

Just get a spring that is strong enough to control the most aggressive side of the cam, and run it on all 16. The other side won't notice a difference.

 

Thanks for all the info. Looks like I have a call to Comp and AFR to make.