What does it do ??
- TBoost is a simple
wiring modification that allows automatic vboost operation on the Vmax to
begin at 3000 instead of 6000 RPM.
What's the point ??
- Stronger mid-range performance is possible by having the vboost open at
an earlier RPM. Stage 7 Dynojet kits even provide devices to eliminate the
vboost butterflys entirely. Many people leave the stock mechanism in place
to facilitate carb sync and sometimes use switches or other devices to
close the vboost tubes at times when enhanced low end and idle are more
important than power.
Having vboost open at lower
RPMs will normally make the bike run rich because of double carbureation
(intake pulses from adjacent cylinders force incoming air back through the
venturi and this double pass picks up more mixture). Usually, if the
vboost is locked "on" all the time it is necessary to install a larger
PAJ2 (secondary pilot air jet) in order to lean out the pilot mixture.
(the stage 7 kit provides DJ190 jets for this purpose).
This modification provides a
means to open the vboost automatically at 1/2 its normal operating RPM.
This provides all the benefits of having vboost open full time while
eliminating the problems associated with having it open at idle and just
off-idle. Using this circuit will allow you to run normal or enhanced
pilot jetting for the sharpest low end performance without sacrificing the
enhanced mid-range performance that open-vboost provides.
How does it work ??
- The vboost control
unit monitors the ignition pulses from the third ignition coil on late
model wiring harnesses and from the second coil on pre '90 harnesses.
Since cylinders 1&3 as well as 2&4 are 180 degrees apart it is possible to
monitor two cylinders at the same time and fool the controller into
thinking the engine is going twice as fast as it really is. Therefore ...
at 3K RPM ... the controller thinks the engine is running at 6K and starts
opening the vboost mechanism (actually the controller begins the opening
slightly earlier ... about 5750 RPM).
Obviously, this circuit has
possibilities for other uses ... such as operating a tachometer that must
be optioned for 4 cylinders (normally a VMax would have to be optioned for
two) and/or other RPM activated devices. I am sure there are other
"Maxers" that have done just that but the purpose of this particular
implementation is to facilitate early vboost operation.
The "S1" switch referred to
in the following sketches and drawings is optional. It provides a simple
means to return to stock RPM activation of the vboost mechanism (6K). When
the switch is open ... it only allows pulses from one cylinder to reach
the vboost controller.