[Land-speed] Finally an LSR Question

drmayf drmayf at mayfco.com
Mon Dec 10 15:00:17 MST 2007


Elon wrote:

>Yes, he is right. A 2.02 intake valve plus 15 psi boost needs about 48 lbs
>to be added when SEATED. -Elon
>
>(snip. . . ) he immediately is adding spring pressure, valve area X boost,
>for a cam change on a motor built by someone else. I'm not sure he's right
>about this. Thanks, BJ in the Bean
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I am sort of ambivalent about this. Here is why. On the intake stroke 
the vlave is open so no added spring pressure is needed. On the 
compression stroke, no added spring is required because the cylinder 
pressure overcomes that. On the exhaust stroke, for a turbo there is 
pressure in the cylinders even after the stroke is completed, so high 
possibility that bo added sprng is needed then either.  And of course, 
on the power stroke the chamber/cyliner pressures are fairly high so no 
added spring is needed then either. So while, I don't think it hurts to 
add a pound or two to the spring rate, the very short times where valve 
overlap might occure and need spring pressure increase is really a short 
timep period. Really short.  That's fora turbo car. On a supercharged 
car, the idea is to remove the burbed junk as rapidly as possible and 
with as littl eback pressure as you can possibly have. So the end of the 
exhaust stroke might need some added rate, but the othere seems to   
pretty much follow the same reasoning?

mayf


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