IMHO perhaps round tube for the plenum with a round butterfly is a valid
possibility.
Maybe cheaper, easier, lighter, more efficient, and better looking.

Terry Adams
Thorp T-18C

Cheaper than $2.75 a foot? Not easier as a round butterfly is harder to make
than a square butterfly. Also harder to get a nice bell mouth shape where
the intake tubes join the plenum. No doubt about it. It looks better to the
average
onlooker.

Paul Lamar

Paul;

I'd guess you've already considered these factors; but my concerns with the
square would be distortion due to pressure differences, and throttle
response.  At idle conditions there is probably about 10 psi pressure on the
outside of that box which makes for some pretty large forces.  I haven't
paid attention, so I don't know what wall thickness you've got.

The issue would be possible distortion of the box in the area of the
throttle plate, which may require clearances to avoid binding that would
limit the low end rpm.  There is also about 160 lbs of force on the plate at
those conditions; so things may need to be a bit beefy.  Distortion of the
plate is also easier to deal with in the round.

Low speed throttle response, although not as important as in a car, is still
a consideration.  With a 4" round it is already an issue, which I'm guessing
would be worse with that big a square.  Or do I misunderstand what you're
intending?

Just some thoughts,

Al

It's 1/8 inch wall Al. Unlikely to distort much. OK Al since this is your 
contention you prove it rather than me using my time. Buy a piece, weld
it closed, install a tubeless tire Schrader valve and  pressuries it with 
10 psi.  Use a dial indicator to measuure the distortion.


Paul Lamar
 
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