How much lift on stock valve springs?

[BlackOmega]

Hey all, looking to get some more lift than the stock cam. However, how much lift can the stock springs take?

 

[gert]

Stock.......... your springs are matched to your cam. if you get a bigger cam more lift/duration you need to match your springs

 

[jdarg]

Hey all, looking to get some more lift than the stock cam. However, how much lift can the stock springs take?

You need to measure ANY set of springs, new or old, stock or aftermarket, to make sure they meet the cam's specs unless you are being sold a matched set. Even then its a good idea. There is no broad answer here, esp. w/ used valve springs.

 

[BlackOmega]

Stock.......... your springs are matched to your cam. if you get a bigger cam more lift/duration you need to match your springs

Thanks, however, Comp Cams regardless of lift, want a lot more seat pressure than stock even if the lift isn't more than stock. In addition, regardless of whether you choose their "small" or "large" performance cam, they ALL call for the exact same spring (on the AMC 258 i6 / 4.2l any way).

And for what it's worth, I've run relatively large cams (.496"/.510" lift) on stock springs, on other engines, with no issues.

So what a spring can "handle", and what it's "designed for" may be vastly different.

Also, too much spring pressure, like above 280# can rip pressed in studs right out of the head.

You need to measure ANY set of springs, new or old, stock or aftermarket, to make sure they meet the cam's specs unless you are being sold a matched set. Even then its a good idea. There is no broad answer here, esp. w/ used valve springs.

True enough. Lets say if it were a brand new set of stock springs.

 

[harleydragon]

.500 absolute max is what I have read...

 

[jdarg]

How much lift the spring can support is a function of the cam's required spring seat pressure. There isn't a one-size-fits-all answer like .500. The same spring @ 50 lbs vs. 100 lbs is going to support less lift @ 100 lbs of seat pressure because its installed height has to be lower to reach the higher seat pressure.

OP you are better off working w/ a cam manufacturer if you don't understand all the variables.

 

[Dan86CJ7]

hmm the machine shop told me when i ordered my comp cam, i didnt need to up grade my springs?? is this incorrect? whats the effect?

 

[harleydragon]

cam lift and duration if it goes radical will require a spring with more seat pressure to keep the valve from bouncing when it seats..other things that require more seat pressure are heavier valves,heavier lifters and higher rpm's..if you are running stock valves and lifters,are not drastically increasing the cam profile or turning high rpm's then stock springs will work..you just need enough spring pressure to keep the valve from bouncing and to give the valve a good enough contact with the head so that it can dissipate heat..any time you go to more high performance parts I would recommend asking the manufacturer their opinion..there are down sides to too much spring pressure.One is the fact that it will require more oil pressure for the hydraulic lifter to move the valve which may require a higher idle speed

 

[BlackOmega]

How much lift the spring can support is a function of the cam's required spring seat pressure. There isn't a one-size-fits-all answer like .500. The same spring @ 50 lbs vs. 100 lbs is going to support less lift @ 100 lbs of seat pressure because its installed height has to be lower to reach the higher seat pressure.

OP you are better off working w/ a cam manufacturer if you don't understand all the variables.

No offense, I know there is no blanket statement, or lift in this case, that would encompass any and all the variables. I am a certified mechanic and I'm very well aware, probably more so than most enthusiasts about the variables.

Perhaps if you have more of the story then you'd understand why I asked this question.

A gentleman brought me an '84 CJ7 and asked me to tell him what's wrong with it. Being that it's 30 years old, pretty much everything needed to be redone or resealed. The engine was really tired.
We decided that rebuilding it would be the best option. It needed to be bored .030" over. The head also needed machining.
After getting the head back, I noticed that the deck surface was scratched and needed to be re-machined. So while we were at it, I had them take a total of .030" off the head.
The machine shop ordered a "master" rebuild kit which included a new stock cam and new springs.
Since we had a new cam already in it, I was looking for a cheap add-on to help with power. Basically, trying to justify the added cost of another cam by keeping the addition cheap.

However, with the engine now being a 262 with higher compression, I would like it to have more lift and a different lobe separation angle.


The stock lobe separation angle is a bit higher than I'd like, 114°. It's meant for more all-around driveability than offroading.
I'd like it to be ~110° to keep the power on the lower end of the RPM scale. Great for trails and can turn the big tires that he wants to put on it.

The stock cam has decent duration, however, the lift is going to be lacking IMO. I'd like it to be around the .500" lift mark.

I'm pretty sure that the stock springs can handle it, I just wanted to know if anyone here had experimented with, or had knowledge of, max lift on "stock" parts.