What aftermarket valve springs to use?

rzimmerl

Registered User
I figured since I was rebuilding the heads I might as well replace the valve springs since they have ??? miles on them. I will be running the stock cam and stock valve ported heads that I have been working on. The heads have been decked 15 thou, and will be running Scorpion 1.73 RR's.

I read a few threads from Dr. Fred running Comp 942 on stock valves, stock rockers with 7.2 pushrods, and a cam. There was also some discussion about stock pushrods possibly bending due to the higher spring pressure of the 942.

Anyone have any info or results running Comp 942 spings?
 
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I have the comp 942 springs with my .520 cam. Unless you have an aftermarket cam, there is no reason to spend the $$ on aftermarket springs. That's my opinion.

In fact, there are some mild cams out there that people use with stock springs as well.

They are a good spring, and fit well with the stock retainers and seats, but they are overkill for your setup.

Jeramie
 
Actually, I disagree with you Jeramie. The stock springs barely hold 75psi on the seat which is not enough when you are running nearly 20psi. I think the 942's are a great upgrade for a stock cam. Just drop them in and go. I've run stock pushrods on much stiffer springs than that with no issues.
 
I forgot to mention that I was running 19psi. The price for the 942's is the same if not cheaper than the stockers.

Thanks for answering my next question about using stock pushrods Dave.
 
Actually, I disagree with you Jeramie. The stock springs barely hold 75psi on the seat which is not enough when you are running nearly 20psi. I think the 942's are a great upgrade for a stock cam. Just drop them in and go. I've run stock pushrods on much stiffer springs than that with no issues.


What do you lose in terms of power running stock springs and 20lbs of boost. I know my springs were set up for the higher boost but what actually happens in the combustion chamber when you jump that high in boost with stock springs?

Ken
 
75 is kind of typical for OHV boosted engines that I have dealt with. For example (and we are dealing with a turbo car the Grand nationals have around a 78-79lb seat pressure. Generally though in a performance application even with a stock cam I'd like to see around a 100 lb seat pressure. Keep in mind too much will beat up your valve train. Unsure what the 942's give you however. I have also heard of people using stock LT1 springs. Be a good tech article to show different spring/valve combinations for stock seat with specs.
 
Here are the specs that I dug up on a search


942 Single
OD- 1.437
ID- .974
Seat Load- 115@ 1.700
Open Load- 284@ 1.200
Coil Bind- 1.125
Rate (lb/in)- 339

Stockers- found this info from Sealed Power, PN# VS-1568
OD- 1.435
ID-
Seat Load- 80.7@ 1.66
Open Load- 187.2@ 1.26
Coil Bind-
Rate (lb/in)-
 
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942's are actually kind of high however we may be limited to the selection of what will fit without machining the heads and for clearence reasons. Again it be a great sticky tech thread
 
I would still like someone to explain why 20lbs of boost doesnt work with high boost application and what actually happen under boost using stock valve springs. Pressures in the combustion chamber should be higher forcing the valve harder against the seat. Maybe I am looking at it all wrong but I am the type of guy who wants to understand why something works the way it does.

Ken
 
found this bit of info on Magnum Powers website regarding the Lightning

http://www.magnumpowers.com/light_spring.php

Introduction:

Some have theorized intake valves in supercharged engines require greater seat pressure (valve closed) then naturally aspirated (NA) engines therefore stronger valve springs are required. This article discusses a theory regarding valve spring requirements and documents dyno results as realized in the supercharged Ford F150 Lightning.

Valve Spring Requirement:

Valve springs return the valve head to its seat after being opened by the cam and holds the valve head against the seat until the camshaft opens the valve again on the next cycle. The valve spring needs to be strong enough to overcome the inertia of the valve train so the valve follows the contour of the camshaft for proper valve action. As RPM increases the inertia increases at the square of rpm requiring much stronger valve springs in high RPM engines. The Valve Train in a push rod engine consists of the valve, valve spring, lifter, push rod and rocker arm. In an overhead cam engine only the valve, valve spring and cam follower are involved. Since there is less mass to overcome in an overhead cam engine the valve springs can be weaker. Engines manufacturers typically install the weakest valve spring possible that will properly close the valve throughout the desired RPM range of the engine. Engine manufacturers use valve spring strength to limit valvetrain wear and useful RPM power band thus designing in a RPM governor all of which improves reliability.

Additional Valve Spring Requirements:

There are two distinct additional requirements a supercharged engine places on valve springs. These requirements are not recognized by leading valve spring manufacturers or most race engine builders and are therefore a new concept to most people looking for increased performance. Firstly supercharged engines require stronger valve springs then NA engines do to a force applied to the valve head that is associated with manifold pressure and the engine’s volumetric efficiency (VE). If for instance a supercharged engine running 20-psi manifold pressure has a volumetric efficiency of 100% when the piston reaches the bottom of the intake stroke and the intake valve closes there will be 20-psi on both sides of the valve head, i.e., 20-psi on the intake manifold side and 20-psi on the cylinder side because the cylinder fully filled with air during the intake cycle. Since the air pressure in this case are the same on both sides of the valve no force is applied to the valve head. If however the engine has a volumetric efficiency of only 50% there will be 20-psi pressure on the manifold side but only 10-psi on the cylinder side when the valve closes, because the cylinder did not completely fill, a net pressure of 10-psi will be present across the valve head. If the intake valve has a surface area of 2.5 square inches a force of 25 pounds (2.5x10) will be generated that will be trying to open the valve thus reducing the effective valve spring pressure by 25 pounds. Since engine manufacturers install valve springs that are only strong enough to support proper valve action to their RPM limit any reduction in effective valve spring strength will lower the useful power band RPM limit. If the valve spring does not have enough strength to keep the valve following the camshaft profile the valve is said to “float”.

The second additional requirement arises during the exhaust cycle. During the exhaust cycle the cylinder pressure drops to zero or can even go negative do to exhaust header-savaging effects. During the exhaust cycle the intake valve spring must be strong enough to hold the intake valve closed against manifold pressure. If the manifold pressure is 20-psi and the valve head has 2.5 square inches of surface area the force attempting to open the valve will be 50 pounds (2.5x20). If the intake valve opens during the exhaust cycle the air/fuel intake charge will flow through the intake valve and out the exhaust valve during the exhaust cycle and will not be used by the engine to develop power.
 
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Ahh, I didn't see that he was running high boost.

Good point.

942's are probably your best option then if you want to stay on the cheap.

Just curious, why all the work and no camshaft upgrade?

Jeramie
 
I would love to put a cam in, but at the moment do not have the extra $400 or so to put it in and more $$ for another tune. I am prob going to add an AFPR in case it starts to lean out to much.

I am going to wait on the cam till I refresh the spare motor I have and get a proven combo for one of the reputable suppliers.
 
I just got of the phone with Comp Cams and they recomend #26918-12 springs @ $152.29 and 786-12 retainers @ $42.86 they said the 942-12 is an ol part#.
 
Those are behive springs and can be had cheaper then that through other sources. I just saw $143 without really looking .

795-12 retainers
613-12 locks

Are these the same ones Dave D was selling or a different Bhive setup?
 
None of that stuff will work. A 26918 is 177lbs @ 1.650 which is the stock installed height. There are other issues as well but it doesn't bear going into them since the installed height is wrong.
 
Why would Comp Cams tell me these are exact upgraded replacements? I specifically told him I wanted to replace my stock springs with some thing that would drop in with a little more spring pressure.
 
Why would Comp Cams tell me these are exact upgraded replacements? I specifically told him I wanted to replace my stock springs with some thing that would drop in with a little more spring pressure.

Because whoever you talked to didn't know anything about the SC engine.
 
Sometimes what can be used and what is a direct drop in are two different things.

They can be used but arnt a direct drop in
 
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