How much lift can stock L98 springs take? I know this has been covered a ton o times, but everyone's always contradicting eachother! I was just wondering if anyone knows FOR A FACT how much they can take.

 

Safely?

About .460 or so.

 

any stock spring needs trashed if you're doing anything to or around them. isn't hard to do nor expensive to run a lot better spring. trash the factory rotator set up too and run aftermarket retainers.

 

They are inadequate for the stock cam. Garbage like all other stock springs.

The car will actually run better, noticeably, with real springs in it, even with the stock cam.

So I guess that means that even a stock cam has too much lift for them..... any lift beyond .000" is too much.

 

You won't actually coil-bind a stock spring until you're up over .500" in most cases. You'll slam the retainers into the valve guides on a stock head (~.470") well before you ever bind up the springs.

HOWEVER.... like everyone here has said- they are completely inadequate for high RPM use. They just don't have enough pressure to control the cam- even a stock one. Shove in an aftermarket cam and valve float can happen at some frighteningly low RPMs- 5000 or even lower depending on how aggressive the cam is. Install 1.6 rockers and the problem is compounded.

Just about all the manufacturers sell valve springs that will drop right into the stock heads and provide MUCH better performance with a mild street performance cam. You're looking for a spring with a 1.25" diameter, 1.70" installed height and about 105-110 lbs of seat pressure (vs. 65-75 for most stock springs).

Don't ditch the stock exhaust valve rotator/retainers unless you have the shims you need to space the spring back up to the correct installed height. The factory machines the exhaust valve spring pocket deper than the intake to make up for the thicker rotator/retainer.

Don't assume that just because you have the right springs in there that all's safe. Like I said, above, most stock GM heads will have contact between the retainer and valve guide (or valve guide seal) at only about .470" valve lift. You have to have them machined down to gain more clearance for a higher lift cam.

 

Damn!!!!! there's always gotta be something......... How much does the average shop charge for machining em down?

 

Who determains the install height of the spring, the spring company or cam company?? This is prob. a stupid question, but I was just wondering? I hope I worded this right.

 

the springs are rated at a set installed height, the spring maker i guess would be the one setting it, but lot of springs are sold by grinders to match their cams. they send the specs out to a spring maker and buy the springs from them and then resale to the end user.

 

Thank's ede, I only ask because I have an Lpe 219/219, and I am gonna use the comp 987's with it.

 

The installer does.

People who supply springs give the installed height that they expect it to be installed at, or at some height that makes their "max lift" spec look good, or sometimes just pure fantasy. When the spring gets put on a set of heads, it's up to the installer to make sure that they are appropriate for the lift and other cam properties in the build, and to set it to the right height with shims or offset keepers or longer valves or whatever. The cam makers help out by supplying believable info for the springs they supply, and will recommend the right spring out of their lineup and the right installed height, to go with their cams.

 

Thank's RB. That makes sense.

 

C'mon guys, anyone know how much machining your heads for a high lift cam costs? I would just ask the mechanics around here but they're all freakin rip-offs for everything.

 

Talk to the racing machine shop that does the work for the round-track racers in your area that win. It's not something you'd get a "mechanic" to do.

I'd recommend getting the guides cut down for use with Teflon seals, since it's basically free to do those 2 things at the same time. One tool, one operation.

 

Haha my bad i meant machinist. Even still, like i said they're all rip-offs over here. And the closest place i can think of otherwise is an hour's drive. So i'm just wondering what some of you guys have paid.

 

Here's a question that I have...where does one find these facts out for a GM factory cam? I know that lot's of people run them (LT4 Hot /ZZ4 and others)! Or does one just look for similar cams and use those spec's?

Thanks DM

 

Yup, that's one way...

Putting more spring than necessary (within reason) doesn't hurt anything, except maybe your wallet, and not even very much there; but too little spring can be fatal to your motor, if one of them breaks while the motor is at speed. The valve will drop into the cylinder. I'll leave the details of what that causes to your imagination, but let's just say that valve fragments are incompressible. See the inside of a motor just once after that's happened, especially if it's your own, and you will never skimp on valve springs again.

GM, having no experience whatsoever with any high-performance springs in any manner way shape or form (even their own factory race teams have always used aftermarket ones) is overly optimistic about the capabilitites of their springs. I will not use any of theirs for anything I build, not even a stock motor; even a stock one will run better with springs that can control the valves' motion.