Fast 95 Z28

Hi, building a 400 sbc with vortec heads and plan to use stock LS3 valve springs. I hear they are good to .575 lift at 1.800" install height. My heads are at 1.698-1.708" install height. The cam I'm using is .500/.518 lift. Am I good or not? I can't find what there rated at for 1.700 install height.

Thanks

allan808

iTrader: (3)

There good to 550 lift, i have 2 brand new sets with retainers pulled off new heads! $65 shipped each.

Mark200

Just do the math... 1.800 - .570 = 1.230 max open (I found the .570 max published in a couple places, no .575)

Your setup is (worst case)... 1.698 - .518 = 1.180

I'm no expert or pro but I'd be uncomfortable with that. You can probably get a +.050 lock to get you to 1.230 open if that doesn't cause clearance problems elsewhere.

Fast 95 Z28

Don't I want that .050" safety margin? Isn't being at 1.230 the max the spring will go? So at 1.180 I'm below it and have a safety margin?

Theres also another cam I'm looking at with .492/.510 lift so I would gain another .008 there too...

Mark200

No. At 1.180 you are .050 below the safety margin. You need to gain .050 somehow if you want to safely (IMHO) use those springs.

Edited to add: I'd really want to know what height coil bind is at, but you may have to test one to find out (GM apparently doesn't publish that data). Barring that I'd conclude that 1.230 is the max safe limit.

Some companies make a valve lock (keeper) that will raise the retainer by .050 -- this would be called a "plus .050" lock (keeper) and give you .050 higher installed height. This may or may not cause interference problems between the retainer and the rocker (you'd have to test fit and measure). They also make one that goes in the opposite direction (a "minus" .050 lock) but you don't want to go that way.
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