DIY_EFI question

[Bruce Bowling]

~ 
~ 
~ Hi,
~ 
~ Using individual throttle bodies with inlet horns (velocity stacks)
~ Anyone know a formula for length of the inlet tract to give ram effect
~ at various rpm?
~ 
~ Mr Bowling's home page has a program but it doesn't take account of
~ valve timing so I'm not sure how useful it would be.
~ 
~ Roger.
~ 

The pulsing effect is caused when the valve slams shut on the head, which
produces a pressure pulse which bounces between the throttle plates and
the valve, so in some sense valve timing IS taken into account.  What is
not taken into account are differing cam profiles, because you want the 
reflected pulse to arrive back when the valve is open, and air temperature
and vapor pressure.  However, the equations on the WWW page, which I
obtained from Superflow, are "empirical" enough to get a close ballpark.
Anything better needs more infomation, and a numerical simulation of
air density, piston speed, valve lift profiles, incident and reflected
wave bounces from the valve/throttle (which will cause diffusion), etc.

- Bruce

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               Bruce A. Bowling
  Staff Scientist - Instrumentation and Controls
 The Continuous Electron Beam Accelerator Facility
    12000 Jefferson Ave - Newport News, VA 23602
                 (804) 249-7240
                bowling at cebaf.gov  
        http://devserve.cebaf.gov/~bowling
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