Lingenfelter recommends 1.90. Whats that mean and how do I do it?

 

I think theyre talking about valvespring installed height. Thats measuered from the spring seat to the bottom of the retainer. Some aplications require a special micrometer to measuer that.

 

Springs are rated by their spring rates. Installing them at a specific height is what determines the spring seat pressure. How much pressure is holding the valve closed. Different spring rates can keep the valves closed at the same pressure but can have much different open pressures.

The spring height is a measurement between the spring seat in the head and the bottom of the spring retainer. If there's too much clearance, shims can be installed under the spring. If there isn't enough clearance there's a number of different ways to increase it.

Cut the spring pockets deeper if the heads will allow it.
A different set of keepers can be used to move the retainer up higher on the valve,
Longer valves.

When changing valve springs to any installed spec other than stock, the pushrod length should be check to make sure you have the proper valve train geometry.

This isn't always something the average backyard mechanic can do depending what work is required. Getting the heads set up properly should be done by a machine shop.

Typical SBC stock springs will have a closed rate in the 80-100 pound range with more performance springs around 120-130 pounds. Very aggressive roller cams can have a closed rate around 300 pounds.

When people talk about valve float, it's not the lifter flying off the cam lobe. It's when the lifter is coming down off the lobe and the valve is being slammed closed by the spring. If the springs are weak, the valve will bounce on the seat and bleed off cylinder pressure and power. Using a stronger spring will eliminate valve float but too strong of a spring can wear out a camshaft from the pressures created when the valve is open.

 

Changing the installed height by way of the keepers doesn't change the push rod length requirements. The valve tip always stays in the same place regardless of where the keepers locate the retainer on the stem, so the push rod requirements stay the same too.

Stock valve spring height on a SBC is usually considered to be 1.700". Aftermarket retainers and keepers usually allow 1.750", which is what most of the aftermarket spring mfrs spec for their entry-level springs (Comp 981 for example). To get to 1.900" installed height, you would typically use longer valves, and possibly offset keepers as well, if you don't cut the heads (or, even if you do, maybe). Most aftermarket heads have the pockets cut deeper out of the box than stock, and are not consistent or universal at all, so for them you just have to measure. The usual drill is to cut the pockets deep enough so that some shim is required; but, not all stock heads can be cut that deep, especially if you want to use larger diameter springs as well, which is almost always the case. You have to be REAL CAREFUL with stock heads.

Yes, some applications require a special micrometer. Those applications can be summed up as "internal combustion engines" (except of course for rotary). If you don't have one of those, it's nearly impossible to do this with any degree of precision; unless you have some sort of snap gauge rig that you've used alot and become accustomed to, by comparing your results against the right tool and consistently obtaining the right measurements with it.

Here's what the correct tool looks like. http://store.summitracing.com/partde...art=CCA%2D4929

If you don't know what you're doing and you don't have the right tools, DON'T try to shadetree it. You can easily wipe out cams, springs, etc.; and those can result in broken parts, valves dropped into cylinders at speed, oil full of metal shavings, and other unpleasant things. It's not rocket science or anything, but it's best to learn by watching somebody that knows what they're doing. Lessons can be expensive otherwise.

 

I posted how to do it in this board about a month ago, search under my old name, NastyL98_T/A

 

I guess I should throw away the old inside mic set then. I've never been that **** about spring installation, and have never lost one. If it gets within ±0.005 or so, I'll go with it. It's only a spring, for chrissakes, and it does have a RATE, after all. As long as the pressure and rate are correct, it doesn't go into coil interference (bind) and has seat pressure, its a good spring. If you want to sit a a bench and test dprings all day long, you'll probably find that the "sets" you buy aren't as close in tolerance as you may believe.

EDIT: My point is that at least as much attention should be paid to the valve installed height (which actually affects geometry) and let the springs fall where they may, within reason, of course. I'd much rather see valve tips all within a few thou and springs that might be ± 0.020" than the other way around.