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Valve Spring Stiffness Pontiac 400?

12K views 8 replies 4 participants last post by  LATECH 
#1 ·
I am using a Sum2802 cam (0.466 int./0.488 exh.) so going by the lift greater than .470" rule it's time to go with after market valve springs. For this cam Summit recommends CompCams 988-16 valve springs which have a spring rate of 230 lbs/in.

However a friend recommends I go with CompCams 995-16 valve springs which have a spring rate of 402 lbs./in.

Is the CompCams 995 too stiff for my cam lobes? If I use the 995 spring would it wear more on the lobe compared to 988 spring?

I am trying to find balance between valve train stability and longevity.

I am using a milled 6x-4 head with Crower 5/16" push rods.

http://www.summitracing.com/parts/cca-988-16/overview/
http://www.summitracing.com/parts/CCA-995-16/

Thanks,
bt
 
#2 ·
The 988-16 would be the right choice.
Installed height should have around 125 lbs
Over the nose (installed height plus the .470 lift) will end up around 275 lbs.
When you get to 300 or over , excessive wear can be an issue.
You wont need THAT much pressure on your motor unless you are going to wind it over 6200 rpm
 
#3 ·
On Pontiacs you have to know what the installed height is so you can adjust the seat pressure. Use the lightest spring that will give valve train control and a decent installed pressure. Usually less than 115 lbs on a hydraulic flat tappet cam.

Pontiacs, in general, have very short valve springs and are difficult to get an off the shelf "just right" spring for.:thumbup:
 
#4 ·
I am running the crane h-272-2 in my (389)400
I used the comp cams 988-16
I set them up with125 lbs installed.Just over 275 over the nose(480 lift intake.
I have wound the dog pee outta that motor and it has never whimpered.
Keep in mind I have forged internals.(pistons -rods)


Yes 115 would be a tad kinder at installed, but I wanted to be at 275lbs over the nose , with the spring rate the 988 have I had to shim the installed height to 125 to get to 275 over the nose (installed height plus 480 lift)
 

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#6 ·
OK. I used the crower 68404 springs.


338 rate
1.56 installed height -- 126.5 lbs
1.080 over the nose-- 288 lbs


My Bad.Sorry.
I do remember they weren't quite at 288 over the nose on the gauge. But I trust the gauge used.
 
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