Building a Flow bench

[efi_student]

Have you seen any of Larry Widmer's work?  His exhaust ports are
trans-sonic for just that reason.  Check out:

http://www.theoldone.com/articles/The_Soft_Head_1999/

The site also has references to a couple of articles in Hot Rod and
Circle Track in the mid 80's.  Lots of interesting concepts discussed on
the site, and of course Widmer is very opinionated.  That alone makes
for interesting reading, but he does have some pretty big time
competitors on his product resume.  I just wish he wasn't completely
focused on Hondas.

Lance

-----Original Message-----
From: owner-diy_efi at diy-efi.org [mailto:owner-diy_efi at diy-efi.org] On
Behalf Of Greg Hermann
Sent: Friday, February 01, 2002 7:41 PM
To: diy_efi at diy-efi.org
Subject: Re: Building a Flow bench


At 1:45 PM 2/1/02, steve ravet wrote:
>Greg Hermann wrote:
>> If you want to do "off-standard" testing, fine. I was just outlining 
>> what would be needed to do _repeatable_ work, on standard.
>
>One question from someone who obviously isn't an ME:
>
>Measuring flow at a lower pressure ratio may not be comparable to 
>published numbers but is it useful for relative comparisons?  When 
>porting or whatever could you do something that would improve your flow

>on the bench but be ineffective or actually worse on the car?

It's OK, up to a point. I don't KNOW for sure, but I suspect that the
two standard numbers (25 and 28 inches of H2O) evolved because
somewhere, sometime somebody figured out that that is about how much
pressure drop there is across a typical intake port under maximum HP
flow conditions.

Why would it be important?? Because comparable pressure drop to
operating conditions would mean testing at comparable velocities.
Scaling back the pressure drop (and therefore the velocity) for testing
would be sort of OK, to a point--BUT--when things like flow separation
start to raise their head, low velocity testing wouldn't correlate very
well at all to high velocity testing.

And--flow separation downstream of the short side radius in an intake
port IS a _BIG_ deal in the real world!

As for testing exhaust ports on a flow bench--it can help marginally,
but unless you're in a position to test the exhaust ports with choked
(sonic) flow at or just downstream of the valve curtain area, at low
valve lifts, you're really NOT going to be looking at the most
significant flow regime which occurs in an exhaust port (during
blowdown) ! (HI Dave!!)

Would REALLY be fascinating to see what would happen if somebody were to
figure out a way to work a convergent--divergent nozzle into an exhaust
port--so that the first pulse of flow down a header tube would be
trans-sonic !!! _THAT_ would make for some serious scavenging pulses !

Greg
>
>--steve
>
>--
>Steve Ravet
>steve.ravet at arm.com
>ARM,Inc.
>www.arm.com
>
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