[EFI] Re: [EFI] Re: Building a Flow bench

[Brian Dessent]

Daniel Houlton wrote:

> Yes, I would want some oxygen to get into the engine.  Which is
> why I'm questioning why you'd use less than 1 psi to flow test
> a head when there's in the order of 14 psi (on a NA motor)
> pushing through the intake valve at WOT?

There may be atmospheric pressure on the upstream side of the port but
that doesn't mean the cylinder has a vacuum, in fact it's probably quite
close to atmospheric as well, depending on about a million factors (cam
timing, exhaust backpressure, etc...)  That nice 18"Hg idle vacuum is
created by the throttle plate being closed.  The actual pressure
difference across the head at WOT is probably quite close to 25" or 28"
WC.

As far as a flow bench is concerned... I did a quick calculation, and it
seems that if you took a 20 gallon tank, pressurized it to 120 psi
(assuming you do it slowly or let it cool), then could somehow release
it very quickly, you could achieve your 25" water column pressure at 200
cfm for like 6-7 seconds.  The numbers are approximate, and the valving
would probably be really tough, but it would let you take your time
building up the air mass with any old compressor and then let it go in a
hurry.  I've also completely avoided the temperature / condensation
issue.  But hey, it's a shot.  I'm sure someone's tried it and failed.

Brian

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