Throttle Plate Control

robert dingli r.dingli at
Fri May 12 01:20:37 GMT 1995

Ed wrote,
> Lou Faustini wrote:
> >    Didn't the Corvette ZR-1 use a servo-motor to control the _secondary_ set
> >of throttle plates?  
> As I recall, the ZR-1 has dual runners going to each port.  There is a
> butterfly valve in each secondary runner which is opened by a motor at
> the PCM's command for WOT operation.  If you are using the valet key,
> the secondary butterflies are not commanded open, significantly reducing
> airflow.  This is not quite the same thing as a "secondary throttle
> plate", but perhaps it's what Lou is talking about.
> At the Detroit Auto Show in January I observed the Lexus 4.0l motor had
> two distinct throttle plates of identical size in series in the throttle
> body, the second apparently actuated by a servo, the first mechanically.
> It appears that engine has a true secondary throttle plate.  I have no
> idea what it is for, but I'm guessing idle control at the very least.
> The motor also has twin distributors!  Imagine that in this day of
> direct ignition.  Must be their secret to high CAMIP and J.D. Power
> ratings.  Of course, they all run and hide when I meet them at the
> light...

The Toyota (Lexus) twin throttle plate (in series) system is for traction
control.  They have been using it on Japanese spec 1GG 2lt 6 cyl engines
for quite a few years along with a dual plenumn that switches between
one and two sections (making the engine effectively two 3 cylinder systems)
and dual intake runners per cylinder.  That totals 9 individual butterflies
(one of which is user controlled).  They also use the twin intake runner 
system for their 4AG (NA and supercharged) and 3SG (NA and turbo) 4 cyl 

The engines use one intake runner per cylinder below about 4500 rpm
and open the second after that.  It sounds like a different system to
the Corvette control in that the intake control signal is a function of 
engine speed and is used to maximise cylinder filling through ram effects.
Some people have speculated that the Toyota system was developed due to 
oversize intake port design.  Later model 3SG engines with smaller intake
ports (except for the turbo version used in the GT4) use a different system 
of switching in a secondary plenumn (shortening the intake length) at high 
speeds to aid resonant effects.  The engines are factory red lined at 7800 

I have also seen research into the topic by Mercedes Benz.  Their work
concluded that there was little benefit for V8s given the intake phasing and
restrictions on packaging the intake system.

Our Lancia research engine has two sets of runners (short and long) which are
also selected according to engine speed.

The reason I have mentioned all this is that there are many other interesting
possibilities that DIY efi opens up.  Perhaps we could start a list of non 
standard engine control variables to ensure that a generic DIY system has 
the capibilty of providing the control required.

Robert 'currently fitting an MR2 3SG into a '76 Celica' Dingli
             Robert Dingli           r.dingli at

Power and Control Systems                 Thermodynamics Research Lab
Electrical Engineering                    Mechanical Engineering
   (+613) 344 7966                           (+613) 344 6728
  University of Melbourne, Parkville, 3052, Victoria, AUSTRALIA

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