In laymens terms, what is the difference between a valve spring with 64lbs @ 35.5 mm and 70lbs @ 35.5mm?

Force (some people call this pressure), wire dia., length, coils, quality of steel, etc…
The 70lbs spring looks better at install height, but what about over the noise?
Need to check install and over the noise (this would be full lift).

So, the 70lbs spring may be noisier, but with have less chance of valve float?

Harmonics, heat and aggressive cam shafts will shorten valve spring life.

There should be no noise, if there is, check valve adjustment or retainer or bucket hitting something.

So, the 70lbs spring may be noisier, but with have less chance of valve float?

NO. It depends on the camshaft used and the valve itself. You need to use the proper spring with the cam/rpm/valve assy as a set. You can't just grab stuff off the shelf and expect it to work properly. Also have the springs checked (almsot any shop that does head work will do this). They have a tool that is basically a micrometer that goes inside the spring then the spring is loaded to its install height and the force is measured. Spring preload is critical to lessen the chance of valve float and other issues. They are just coils of wire....so no two will ever be dead on as far as installed height vs preload....that is why thier are shims that go under the spring to adjust spring tension (or precision machining pocket in case there is too much tension)...head work is an art and science all in itself....don't guess on it....and never take anyones word on specs. I always check specs on a cam and springs...and make sure you know what lift/duration and lobe seperation measurements are taken at. Some companies take it at .050" lift of cam....some are taken from base circle....if you are in the least confused.....have a pro do it...or someone walk you through it...smacking a valve due to too little spring or a spring that goes into resonance is a bad thing.....resonance is another issue all together....that is why some spring kits are dual spring....they can alter resonance and still keep installed height and preload where they want it.

Ok, then how do you pick the proper spring to match the cam specs?

Ok, then how do you pick the proper spring to match the cam specs?


Buy the ones the manufacturer recommends...or have the shop doing the work do the footwork. Cam cards used to tell you what seat pressure was needed....and from that you need to check the installed height of springs to make sure they do not go into bind...it is easier just to buy the kit as a whole rather than putting it together unless you are a pro (or the shop)....

Well, I bought the helix cams w/o springs 'cause I knew I was getting oversized valves which helix does not have. Now I need to know what to get.

Well, I bought the helix cams w/o springs 'cause I knew I was getting oversized valves which helix does not have. Now I need to know what to get.

Best I can suggest is talk to the shop doing the install...they will be able to figure it out. The Helix springs and retainers will work....the valves are not that much larger to cause issue as far as I am concerned...but I would talk to the people that sold them or is going to install them....

Initially, I was going to have a machine shop work the heads then have a subaru master tech install everything. The tech *seemed* competent and knowledgable when I was asking him various questions.

He has done work for me previously, I have a aftermarket gearset and he seemed to have no problems replacing the synchros and shift hub assemblies.

Initially, I was going to have a machine shop work the heads then have a subaru master tech install everything. The tech *seemed* competent and knowledgable when I was asking him various questions.

He has done work for me previously, I have a aftermarket gearset and he seemed to have no problems replacing the synchros and shift hub assemblies.


Dude just because someone can do a tranny does not mean they can install aftermarket stuff into a head assy. The machine shop that does the machining should be the ones that finishes everything. Headwork is nothing to be played with.

You need an engine builder, not a mechanic. There is a lot that goes into selecting valve springs so I have left it to the pros. The big ones are the binding height--get that too big and you'll break stuff--and the poundage of the springs for high lift cams.

I like the "beehive" springs because the spring rate adjusts with lift, keeping relatively low tension around the base circle. DPR Racing sells them and I think Kelford may make them.

Most of the double springs are going to have low binding heights because the wire is thinner.