ox sensor on sequential efi,high overlap cam....

[Greg Hermann]

>When lift = 25% of valve diameter, the "curtain area" of the valve equals
>the throat area.  Actual flow usually increases at higher lift but not much.
>A valve cannot be opened rapidly to this point and held for a while, then
>closed rapidly.  The dynamics of a mass/spring system prevent this.  A valve
>is first kicked open by the cam.  Then the spring tries to stop it and
>reverse its direction, then the valve is caught by the closing ramp.  The
>physics of this motion dictate the cam profile.  More lift/duration requires
>stronger parts and or reduced life.

AS I said, this is true ONLY when the valve is UNSHROUDED in its real world
environment. Take a look at the max lift for drag (or NASCAR) race cams for
hemi headed engines vs. those for wedge chambered engines. Because of valve
SHROUDING, wedge chambered valves will see increases in flow at lifts
beyond 25% of valve head diameter. This is a PROVEN fact, both on flow
benches and in racing. This fact is just one of the many proven performance
advantages of the hemi chamber!!

AND -NO, the physics of the situation DO NOT prevent operating a valve in
the manner I described, any more than they prevent the valve from residing
in one position (on its seat in a closed position) for a finite length of
time during each cycle. YES, this kind of a cam profile would require
stiffer valve springs, and stronger, more expensive, lower friction valve
gear to get the job done. And "ramps" at the top of the lift curve as well
as at the bottom. Because higher valve acceleration rates are required to
do it this way. And because the valve would have to be stopped smoothly at
the top of its lift, just as it is at the bottom. But as long as the cam
profile is designed so as to keep the derivative of JERK to a minimum, and
the springs are properly damped, the physics will be fine.

 (The word "JERK" is not used as an editorial term here, it is the
appropriate and correct technical term for the first derivative (rate of
change) of acceleration! :-) What I am talking about above is the next
derivative still--the rate of change of Jerk. Never have heard a formal
techy term for it, but I suppose you could call it "smoothness".

But the whole idea of what we do is to get more performance by spending
more money on neater parts--and the kind of cam profile described is most
certainly one way to do it!!

Regards, Greg
>
>Gary Derian <gderian at cybergate.net>
>>
>>Then why don't they stop the valve at the optimum lift point, and leave it
>>there longer, instead of just stretching out an existing valve lift curves
>>duration, and increasing lift by doing so?? Too much work to develop a
>>really unique profile for each grind??? Yep, I AM a cynic!! :-)


>>