I was stripping down my 1988 turbo throttle body for use
on the dyno engine and I came on two sets of dual butterflies
one after the other. Does anybody know why Mazda did this?
There is one large one and two sets of dual in the other
two throats. News to me.

Paul Lamar

Hi Paul,

yep! found them in every one of the three throttle bodies I have - up to and
including the 1990.  My understanding is that they are there to prevent
airflow into the secondaries until there is sufficient airflow/rpm? into the
engine.  If you stomped on the throttle at very low rpm the second set of
butterfly plates (one further in toward the engine) can be made to open via
their physical linkage to the throttle shaft.  If  rpm is too low when you
stomp on the throttle this opening of the secondaries could cause engine
performance to suffer/stumble.  The  control system will not permit the
first butterflys in the air flow stream to open until the control conditions
criteria (what ever it is) is met even if the second set (are opened by the
linkage).  That is what I have been told.  Sounded plauseable to me.

Best Regards

Ed Anderson

Well I took them out and found out the shaft was very useful.
More on that later.

It was real hard to break those four little screws loose. I wound
up using a Dremal tool to grind down the sides of the screw
heads so I could get a small vice grip on them. I guess Mazda
did not want them coming loose and going through the engine.

There are three stock 1.78" ID throats with a total area of 7.2 
square inches. A single throat of the same area would have 
less pressure loss.

Using the shaft that came out of it... it is possible to
build a light weight single throat TB with a 3.5 inch ID or 9.6 
square inches. Much like you and Chuck did. That shaft would be 
hard to fab if I had to make one. I'll do that some time in 
the future.

A single throat of the same area would have less pressure loss.
A bigger one even less. I'll measure the stock pressure loss
on the dyno using just the dual and then the dual and the single.
It makes no sense what so ever to have any TB pressure loss in 
an engine that runs WOT 90% of the time. Pressure loss equals HP
loss.

Furthermore after getting everything off I could... the stock TB 
still weighed three pounds! 

BTW I arranged the linkage so the single and the dual butterflies
open at the same time.

Paul Lamar
 
The AirCraft Rotary Engine NewsLetter.  Powered by Linux.
ACRE NL web site. http://home.earthlink.net/~rotaryeng/            
Copyright 1998-2003 All world wide rights reserved.