Goofy intake

[Jonathan Coates <jon@domain.elided>]

Original message:-


Date: Sun, 2 Feb 2003 23:32:21 -0500
From: "Paul  Misencik" <paul@domain.elided>
Subject: Goofy intake?

Speaking of throttle response, I was looking at the (stock) intake on my 
'87
Spider today and got to thinking...

Why did Alfa choose to run the intake hose all the way across the top of 
the
engine and way over to the airflow meter on the other side of the engine 
bay?
Was it just for packaging reasons?  I mean, the throttle is on the 
passeneger
side of the cylinder head, but the airflow meter is hell and gone, all the 
way
on the other side of the engine.  The intake air has to come all the way
across a hot cylinder head, which I would think would heat it up somewhat,
making it less dense.  Worse, what happens to all that air when I shut the
throttle?  When I'm accelerating, it's drawing air through this huge tube, 
but
then I lift and the throttle closes, there is a ton of moving air in 
between
the air flow meter and the throttle itself that just... stops, right?

That seems stupid to me, because then when I get back on the throttle, the
initial burst of intake air has to start moving again from a dead stop, 
which
seems like it would rob the initial throttle response of the engine.

I know Alfa engineers are smart, so is there some theory at work here that 
I'm
not understanding?  (It sure wouldn't be the first time.)  Has anyone - 
even
in a racing application - every tried to change the way this is set up?

Paul Misencik


The main issue is getting an even airflow, without pulses, at the air flow 
meter. If you have the AFM in an airflow that is pulsing, you will need to 
add damping to stop the meter flap from shaking back and forth. This 
damping will reduce the throttle response.
Also the velocity of the air through the ducting at WOT will be high enough 
to reduce the temperature rise in the air to virtually zero.
HTH
Jonathan Coates
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