Aftermarket Valve Springs
By: Motoxxxman
(From: http://preludepower.com/forums/showthread.php?t=292538)

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So after lots and lots of researching, I've found a set of aftermarket valve springs that are a direct install in our engines, and even work with our stock retainers!!
They are stiffer than stock, and have a great deal of travel for those aftermarket cam regrinds with decent lifts.

Supertech H1000d Valve Spring (part# SPR-H1000d on ebay)
29.65mm OD Outer Spring
21.85mm ID Outer Spring
20.50mm OD inner Spring
15.50mm ID Inner Spring
80 lbs seat pressure @ 35.50mm
239 lbs @ 12.5mm Lift
14.80mm max net lift
20.70mm coil bind
12.80 lbs/mm rate

Supertech performance valve springs are made with premium Superclean Chrome Silicon Vanadium Steel Alloy for higher performance and durability. Computer designed to ensure that wire stress levels do not overpass the limits for long durability under extreme conditions and harmonics are well under control.

Pay close attention to the spring pressures. The above spring kit is meant for the h22, which has a shorter installed spring height than our 3g engines. Which means the pressures will be a bit lower in our engines than what is described above. It also means the retainers will bottom out on the valve seal waaay before the springs themselves bind.
This spring kit is the only h22 kit where both the inner and outer springs fit our engines.
The above specs show 80lbs of spring pressure at 35.5mm of spring height, which is the approximate installed height in an h22. our engines run 36.75mm.
these are my calculated spring pressures for these springs when used in our engines with the stock b20/b21 retainers:
65 lbs seat pressure @ 36.75mm (this is the pressure when the valves are fully closed)
181 lbs @ peak lift with stock b20/b21 cams (0.356"-0.366" lift)
195 lbs @ peak lift with colt cams regrinds or web cams regrinds (0.410"-0.415" lift)

I haven't measured stock spring pressures for comparison, but you can definitely count on them being a good deal lower. My guess is around 30-35lbs seat pressure, and 130lbs or so at peak lift.

Yes we do have a winner. But only use the supertech h22 inners or the outers, not both, and whichever you dont use, use the stock springs.
using both inner and outer supertech h22 springs is too stiff, and you risk damaging a cam and/or cam cap.

Just remember guys, Supertech springs are the only ones I've actually measured. So other brand springs may or may not fit or work. These supertech springs are thicker than stock, and do come very close to touching the cam journal edges (the recesses cut out for the springs), but they have about 1mm clearance all around. So springs that are wider in diameter, or same diameter but thicker coil, or both, will touch the head. So if you consider using a different brand spring, make sure to have that be the first thing you check.