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

I stumbled onto this article by Charles of Magnum Powers.....he and Fast Specialties put a lot of work into this and it is very much worth reading.

Dale

 

That's a good find!

 

read it last night.

Basically confirms all the research I've done since Charles first hinted it could be the valve springs limiting rob's 1st engine.

 

I agree with Dale, this is a great read on the valve springs and explains alot that has been going on with several trucks latley, who with the MP blower are seeing more power than we ever before thought.

JimIII

 

Great article, I guess knowledge is key when trying to get the most out of a motor huh?
Wheres my new springs J3????

 

Good read, when are the 120# springs going to be available?

 

It sounds very technical...

Call Comp Cams, ask them about spring set-ups for boosted applications. They have a little bit of experience...

 

Comp specs an 88# seat pressure for their springs, Crane has 85# and Crower has no specs. This from each companies website.

 

They will be available in about 2-3 weeks, we have 105#s now but Im not sure how many sets are on the shelf for sale, we are about to be assembling some motors and heads/cams so I know some if not all are spoken for. But they can be here in a few days notice. It is very evident that the valves are floating on these trucks. You can call comp and they will give you information read from the book. Or you can take advice and testing conclusions from aftermarket companies who specialize in your exact vehicle and applications.

JimIII

 

Well I guess that answers that huh!

 

Thanks for the quick updates and info.

 

Just a couple of questions? Not trying to be difficult just being an engineer and pretty knowledgeable on springs in general.

The rating that you are specifying (88lbs, 105lbs, etc.), Are you specifying the force applied to the valve seat or the actual spring rate in "lbs/in" as most springs are specified? That seems extremely low if it is the actual spring rate. If this spec is the force applied to the seat this is an arbitrary way of specifying a spring and really means nothing on a spring spec because the seat force can be manipulated without changing the spring rate.

Creating a higher seat pressure without changing the spring rate can be achieved in at least two ways: shimming the orginal spring to create a higher preload, or using a longer spring with the same spring rate which results in a higher installed preload. Simply adjusting the preload (or the seat pressure) on a stock spring rate may keep the valve from leaking when in the closed position when running high boost but doesn't really give you the ability to run a much more aggressive acceleration curve on the cam design, because the spring pressure on the closing side of the cam curve (where valve float occurs) is only increased by the extra preload amount 20lbs-50lbs (what ever the difference in preload was set to).

My point in writing this is that if you are needing a new valve springs because of a more aggressive cam and/or running higher boost you will need to know two things about the spring in addition to the physical fit, size, and allowable compression:

1) The actual Spring rate (lbs/in) Which doesn't necessarly need to be increased unless a more aggressive cam profile requires it.
2) The pre-load (lbs) when installed, but this is a function of several variables including the spring rate and physical spring geometry. This parameter should be increased in higher boost setups, but would not necessarly need to be increased if boost was kept low, even if a more aggresive cam was installed as long as a spring with a higher spring rate was used.

 

Don't forget the lengths (both compressed and uncompressed). Not directly related to the spring rate but will affect the valve tension.

 

That is an important part of the physical design.

I see where valve springs don't directly list the spring rate, instead they list the compressed (open) and uncompressed (closed) force it applies. It still gives the same information. Along with the physical design being correct (enough movement for cam lift...etc) That compressed (open) spec is also important in addition to the closed spec that the builders are refering to. It has to be high enough to prevent valve float on the decelerating side (closing the valve after cam has gone over center). But you don't want it to be a lot of overkill because that would waste a lot of engine power compressing more spring than you have to and cause addition wear to bearing and contact surfaces.

 

That's one issue I have with the MP article. The article can leave the reader with the impression that cost of manufacture and acting as an inherent rev limiter are why manufacturers use marginal (i.e., just enough pressure to do the job) springs.

The two points that you raise above are far better explanations for "weak" springs. Even with synthetic oils, excessive spring pressure is bad news for the valvetrain.