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Date: Wed, 7 Oct 2009 08:33:42 -0400
Message-ID: <1ab24f410910070533w6d5f43e0mff89e55f13ac00a5@mail.gmail.com>
Subject: Balls and Springs
From: Lynn Hanover <lehanover@gmail.com>
To: flyrotary@lancaironline.net
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Lynn,
  Do you know how short the intake actually was and I presume this was a
 13B fueled by a carburetor dynoed by Drummond ?..............

The engine is a 12A with a Weber and 38MM chokes. A 13B would be about 10%
better.
The sheet is from Daryls computer dyno. He did some passes for Tracy years
ago using his injection control unit.

That particular intake is still on the engine in my shop. It looks just like
any aftermarket 12-A intake but he has them made from his design. His
runners are very small about the same size as a stock Mazda intake. It uses
a stock manifold gasket. I think most aftermarket stuff has the runners too
big, and also there is not enough meat to go bigger if you need to use
hogged out 6 port end irons or turbo end irons for some applications. We are
limited to 38MM chokes in a 48 IDF Weber so going bigger just costs low end
torque.  If forced to guess, I would say about 8 inches from flange to
flange.

The smaller runners keep the velocity high and help torque over a wider
range of RPM. Probably not a problem in aircraft, once you get the runner
length right. Bigger runners move best power up the RPM range, and make
tuning more important.

Lynn E. Hanover

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<div>Lynn,</div>
<div>=A0 Do you know how short the intake actually was and I presume this w=
as a</div>
<div>=A013B fueled by a carburetor=A0dynoed by Drummond ?..............</di=
v>
<div>=A0</div>
<div>The engine is a 12A with a Weber and 38MM chokes. A 13B would be about=
 10% better.</div>
<div>The sheet is from Daryls computer dyno. He did=A0some passes=A0for Tra=
cy years ago using his injection control unit. </div>
<div>=A0</div>
<div>That particular intake is still on the engine in my shop. It looks jus=
t like any aftermarket 12-A intake but he has them made from his design. Hi=
s runners are very small about the same size as a stock Mazda intake. It us=
es a stock manifold gasket. I think most aftermarket stuff has the runners =
too big, and also there is not enough meat to go bigger if you need to use =
hogged out 6 port end irons or turbo end irons for some applications. We ar=
e limited to 38MM chokes in a 48 IDF Weber so going bigger just costs low e=
nd torque. =A0If forced to guess, I would say about=A08 inches from flange =
to flange. </div>

<div>=A0</div>
<div>The smaller runners keep the velocity high and help torque over a wide=
r range of RPM. Probably not a problem in aircraft, once you get the runner=
 length right. Bigger runners move best power up the RPM range, and make tu=
ning more important.=A0=A0</div>

<div>=A0</div>
<div>Lynn E. Hanover</div>

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