I found a very nice throttle body from 2L turbo Nissan. The ID is 2

5/16" . I

wander if it's big enough diameter for my NA 13B,
or I should look for a wider one?
Bulent

Ed Anderson wrote:

The 2 5/16" dia would only give you around 4.2 Square inches of inlet,

the

three openings (45mm dia) on the 13B turbo throttle body I have give a

total

of around 7.3 square inches, so I would think the Nissan one might be a
little on the small size.

Al Gietzen wrote:

Going too large on the TB has the disadvantage of less control precision and
possible too low air velocity; depending on where your injectors are.  Just
from my talks with folks who've run these things on dynos and race cars, I'd
guess around 4 3/4 to 5 sq. in. area for a 2 rotor.

Al

The throttle body is on the upstream side of the plenum chamber so the velocity
of the air is always changing as it makes its way through the system. Most people
put the injectors near the ports. (Not the best place IMHO). As the port opens 
and closes the velocity of the air through the intake port changes rapidly. What 
you don't want is pumping losses in an engine. Lower velocity in all parts of the 
intake system with a given mass of airflow means lower pumping losses. Lower 
pumping losses gives better BSFC (lower fuel consumption) and power.

The Mazda four rotor at Lemans not only had excellent power it also had a low BSFC.
The race car won Lemans outright in 1991 beating all the legendary european makes
such as Mercedes, Porches, Ferrari, etc., etc.. Not only that it beat them when the rules
called for a limited amount of fuel for the entire 24 hour race. I think it was the only 
Japanese engine to ever win Lemans outright but I could be wrong about that.

A two rotor version of this engine would give 240 HP at 6000 RPM.
Here is a cross section of the induction system and rotor housing.
This engine had a slide throttle. When the throttle was wide open the pipes
had a straight shot with no restrictions what so ever. Wide open throttles
are typical for aircraft engines at high altitude cruise.

Frankly I think restricting the diameter of intake ports or other parts to improve 
HP is another urban myth. It may mix the air and fuel better at low throttle openings 
but moving the injectors out towards the bell mouths on the intake tubes 
will also do that.

BTW They are in the welders Ken :-)
 
Paul Lamar
 
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