[Diy_efi] Intake manifold flow testing

[Bill Washington]

Gents,
    My two bob's worth:
The blower will give a continuous even flow through the manifold - This 
isn't even close to real life on the engine particularly at low RPM where:
1. flow in each runner starts and stops sequentially with the opening 
and closing of intake valves.
2. The opening and closing of the valves cause low and high pressure 
pulses which propagate through the manifold at the speed of sound. 
(NOTE: since the speed of sound is airdensity(pressure) dependent the 
speed of propagation of these pulses will vary with vacuum/boost, which 
in turn is affected by engine speed, throttle butterfly position, turbo 
speed, ambient air density, moisture content, Intake/filter 
restrictions, shape and internal surface finish of the manifold ETC, ETC!)
3. When the high pressure pulse from one intake valve closing reaches 
another intake valve while it is open that cylinder will receive a 
better charge of air.
4. When the low pressure pulse from one intake valve opening reaches 
another intake valve while it is open that cylinder will receive a 
smaller charge of air.
5. Not only does the propagation time vary with the factors mentioned in 
(2) above, but also the time between intake valves opening varies 
linearly with RPM.

Therefore I would expect that greatest effect from these factors will be 
at low RPM, which seems to be borne out by other people's experience, 
whereas at higher RPM I would expect the performance to asymptote 
towards the continuous flow model.

Bill W

>------------------------------
>
>Date: Tue, 11 Feb 2003 18:47:47 -0700
From: joeld <joeld at ualberta.ca>
>To: diy_efi at diy-efi.org
>Subject: RE: [Diy_efi] Intake manifold flow testing
>Message-ID: <3E4AE396 at webmail.ualberta.ca>
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>Reply-To: List for general do-it-yourself EFI talk <diy_efi at diy-efi.org>
>Message: 3
>
>I would imagine blowing through would not get you the same ratios as a vacum 
>(real engine) would.
>
>example: two stroke porting for normal engines can be a huge deal, everything 
>should be extremely smooth. if supercharging, it really does not matter, only 
>that your areas are correct.
>
>also there would be no resonance with this setup, i think that could lead to 
>some major blunders
>
>Joel Day
>C.S.C 2003 Team Leader
>PH: 434 9294
>www.ualberta.ca/~uacsc
>
>
>  
>



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