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Discussion Starter · #1 ·
If/when you buy new valve springs for your engine, or if you want to check the existing springs:
A) get a spring height/pressure measuring machine/tool and verify that all your springs for exhaust and all your springs for intake have the same parameters:
A) same pressure at compressed height
B) same pressure at installed height

You may marvel to find just how far out of wack your spring pressures are at their heights.
Were I to be dealing with a parts source where I could just return what I did not use, I would be tempted to order three or four sets of springs, measuring and recording ALL of their pressures and heights on a spring measuring device (lever with a twin dial: height and pressure.)

I would then find, out of that set of springs, the eight for each type (exhaust and intake) that most closely matched each other in pressure at installed and compressed heights, and had the highest rates. I would box up and return the other springs to the parts place. Then, I would get spring shims (yes, they do exist) and shim the springs with the lowest pressure at installed height until they at least matched the spring rate of the springs in the chosen bunch with the highest rate when installed.

This sort of thing is a relatively completely forgotten art, but it will help your engine's consistency.

Whenever you have your springs accessible, you can re-check the springs for consistency, and re-shim them unless they are fatigued beyond sanity, and need to be replaced.

The goal, whether you have two cylinders or 20, is to have each cylinder an exact replica of the other one(s.)

On that note, it may surprise you to know that some racers machined their single-plane intake manifolds under their four-barrel carbs so that the shorter intake runners (closest to center of engine) had the same internal volume as the longer ones. This struck me as odd, due to a shorter runner having a different set of harmonics than a longer one, regardless of cross-section, but, the net effect would be that intake air pulses would, in theory, then arrive at the carburetor relatively evenly spaced, making consistency on a per-cylinder basis easier to achieve.

BTW, here's a freebie: if carburetors had longer, more smoothly-transitioned venturii, they would experience a lower pressure drop at WOT than the short little suckers we see to this day, with their violent transitions in diameter, and sharp internal edges. If only carb makers would admit this and do something about it... WAIT, Edelbrock JUST DID THIS, with the introduction of their "4150" series of carburetors, which are an upgraded new, easier-serviceable and more-easily-tuneable version of the venerable Holley 4150. The Venturis are longer on this one.

The ideal carburetor, at WOT, has the same pressure above and below the carburetor, just as the ideal pipe for transporting air has the same pressure at one end as the other, requiring no power to transport air through it. This is ideal, but impossible, but it is a metric one can use to determine a carburetor's efficiency.

Back to the springs: if you are truly devoted to consistency, run all four sets of springs for a few months, THEN test them for compression versus height, after they have been seasoned, but you will have to keep all the sets.
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