Valve Spring Selection

Supe

MalibuRacing Junkie
May 21, 2003
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Charlotte, NC
This topic will be for the discussion of valve spring selection, about what your spring pressure should be giving your cam lift, rpm range etc. Many people go by the recommendation of the cam card without an understanding of why.

Thanks to 638montecarlo for the thread suggestion.
 

juicedimpss

Amateur Racer
Jan 13, 2007
117
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Milwaukee Wi
www.clocksoffracing.com
this is a great topic. When i worked at the speed shop,we had alot of cyl heads that came from shops that didnt spring correctly for the camshaft they sold to people. heads from certain shops always came in with broken springs.
 
A

Anonymous

Guest
Also what makes a cam over/undersprung? Of course the higher the rpm the higher the spring pressure but how do you know how much is too much or too little? Is there a formula on max rpm = a given pressure? I am sure that if you have too much spring pressure you will be wasting energy on the unneeded spring pressure and also the wear on the whole valvetrain. Also I am sure it has to do with valvetrain weight also, like a heavier valve requires a higher pressure spring to close it at a given rpm. I could go on and on!
 

Goob

Top Fueler
Jun 6, 2003
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Indianapolis
638montecarlo said:
Also what makes a cam over/undersprung? Of course the higher the rpm the higher the spring pressure but how do you know how much is too much or too little? Is there a formula on max rpm = a given pressure? I am sure that if you have too much spring pressure you will be wasting energy on the unneeded spring pressure and also the wear on the whole valvetrain. Also I am sure it has to do with valvetrain weight also, like a heavier valve requires a higher pressure spring to close it at a given rpm. I could go on and on!
That is why you have to take the manufacturer recommendation with a few grains of what you know of the rest of your valvetrain. Antiquated master lobe designs, and max performance profiles are really the spring killers. Improper spring pressures wipe out flat tappet stuff as well as rollers.
A weak/broken/improper spring or floating the roller tappets is what usually kills the lifter wheels and cam lobe on the roller stuff. The roller wheel must maintain a reasonable lash and follow the lobe closely.

I've run a hydraulic flat tappet with as little as 85# on the seat and 135# over the nose up to 5800 RPM's with steel valves and retainers.

Depending on the lift and profile, I'll have 125# to 135# on the seat on a mechanical flat tappet, about 300# up to 350# over the nose, the higher end for BBC and large intakes on a SBC to twist up to 7500

Rollers, big spread on what you need there again according to the cam profile, RPM range, and weight of the valvetrain on the valve side of the stud.

Weight on the pushrod side of the rocker stud means nothing, and actually, more is better in most cases.

My cylinder heads get each valve spring individually set up and charted. Valves are stamped for position, and each spring is checked for both seat and open pressures.
 

Goob

Top Fueler
Jun 6, 2003
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Indianapolis
Then you get into whether a triple spring, double spring with or without a dampner spring, etc., etc........

Plus or minus length valves, + or - height retainer locks to get it perfect, etc., etc..........
 

crd89stang

Dragway Regular
Jun 19, 2005
750
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attleboro ma
could also talk about rpm ,boost ,cylinder pressure changing the requirements of springs. how much spring pressure hydraulic lifters can handle etc
 

79Maliboo

Frequent Racer
Mar 11, 2010
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Mount Laurel, NJ
638montecarlo said:
... I am sure that if you have too much spring pressure you will be wasting energy on the unneeded spring pressure...
I was told once upon a time that there is no such thing as wasted energy from spring pressure, as the energy is used to open one spring on the face of the lobe, another lobe is recieving pressure on the backside of the lobe as it closes the valve.

Is there any truth to this?
 

Doober

Moderator
Staff member
Jun 2, 2003
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www.cardomain.com
I believe it becomes wasted when it's outside what winds up being required. Like Goob said you'd need to consider everything with the valvetrain, not just what the mfr. suggests. They don't know if you're running a completely stock style setup, or some extremely lightweight valves/retainers/keepers, those 3 pieces have quite an effect on valvetrain stability.

Another thing to consider pushrod length & weight, although I don't think length is much of a concern compared to weight far as spring pressure is concerned. I've read some use thicker walled/heavy duty pushrods that actually weigh more than stock pieces because of the pressure they're under. When you start adding spring pressure, one of the most-stressed pieces will be the pushrod, because it's taking more pressure than the valve, retainer, or keeper... one of the springs recommended for the cam I currently have is Comp Cams #986 - 270lbs. open pressure. Using a stock SBC rocker ratio that's increased to 405lbs., at 1.6 it's 432lbs., you probably get the picture. Using this stock spring as an example you could see why they recommend aftermarket springs.
http://www.summitracing.com/parts/PIO-RV611-4/Application/?prefilter=1

These of course are my thoughts on the matter, I don't have any in-depth experience in experimenting with different springs, otherwise I could probably go into more detail :)
 

MISFITx408

Daily Driver
Nov 26, 2009
17
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NORTHERN CALIFORNIA
Glad I found this thread. What happens when spring pressure is too stiff for selected cam? I have some untoucheded 906 vortec heads. Cam selection .520/.540 lift with comp 26918 springs. Recently comp revised the said springs and now has an open pressure of about 380 lbs. I was advised to go to a softer spring (26915's) by comps tech advisor at factory installed height. Just curious as to what could occur.
 

cutlass389

Frequent Racer
Feb 2, 2009
684
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NC
I can speak to this one even though I don't have a lot of hands-on experience. When I talked to Comp for beehives for my vortecs they talked me into the 26915's rather than the 918's because of the pressed-in studs. Too much pressure or rpms can pull studs and ruin your day. Also, IIRC, they also advised me that with stock valve guides and seals, the max height with beehives was .530. The springs can take more but the guides need to be cut down.