Miata Mailing List: October 1993, Message #6
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   From: Mike Rother 
Subject: Re: Miata NACA Duct
   Date: Fri, 1 Oct 1993 11:46:53 -0400

	From: "Stephen H. An" 
	Subject: Re: Miata NACA Duct 
	
	    Is it meant to replace the body colored panel that is level
	    with the hood when the headlight is down?  Or does it some
	    how replace the lamp housing?

	Yes. It will be offered in both primer and painted forms. All
	you have to do is unscrew the current panel and swap in the new
	one, it took me about 30 seconds, unless the screws get rusted
	and stuck.

	    air takeoff at the rear that connects into the
	    existing miata air filter assembly?

	I am not sure this is necessary, the objective here is to get
	cooler air into the engine compartment, thus lowering the
	intake air temp, to have additional ducting would alter the
	intake "ramming" (is this a real word) effect, thus altering
	the torque characteristics, plus making the ducting really
	smooth to keep the drag down is fairly hard in that space. And
	lastly, the cost would seriously outweights the benefit.


This is an interesting discussion.  When I ran the experiment of
temperatures at various underhood locations, I found considerable
variation just by moving the temperature probe a few inches.  There
seem to be all sorts of underhood currents and pools at speed.  I'm
sure the NACA duct will help reduce underhood temperatures, but I don't
know how much of that cool air will actually get into the intake.  You
could reshape the intake snorkel to face the NACA duct, but then you
might have the rainwater-entry issue again.

Rerouting my intake to just left of the radiator shroud has made my car
noticeably stronger.  My Miata still doesn't win speed contests, but I
do go up hills and pass with fewer downshifts.  My latest rainshield is
working fine, and I can't imagine going back to the stock intake
snorkel.  However, I'm intested in the NACA duct as an additional
measure for cooling things down under the hood.  I could imagine having
one NACA duct on each headlight cover.  Are there any plans to make
both "left" and "right" ducts??