Maximum torque for the na I5 engine.

[Bernard Littau]

> > Can you detune the engine to meet the power and torque limits?
>
> I am working on it, the problem is to find a trusted dyno facility that
can
> do the measurement. To detune the engine will not be a problem, a retarded
> ignition map and low boost pressure will do the trick. The inspection guys
> would find a throttle limiter in a few minutes.

I would assume they are inspecting the engine _and_ running an emissions
test.  A retarded ignition map will have impact on the emissions.

Why would a throttle limiter be a problem?  Most taxis and rental trucks in
the USA have throttle limiters.  They are there to protect the engine and
help a fleet meet fuel consumption requirements.

Lower boost is the key.  However, you can't just vent boost as venting
metered air would again affect emissions.  You must force the MC wastegate
to bypass the turbo and waste the exhaust.  You could do this electronically
on the ECU if you could amplify the pressure signal from the pressure
transducer in the MC ECU.  You could also do it mechanically by having a
device that amplifies the boost pressure from the manifold before it reached
the ECU.  If the system has no leaks or venting, you could make do with a
larger piston on the manifold side of the boost pushing a smaller piston on
the ECU side.  You would either loose, or amplify, vacuum information, too,
but I don't think this is a problem for the ECU. The electronic route with a
simple op-amp seems easier to me.

I am not yet 100% clear on the true effect of the wastegate spring.  I think
a softer spring might do something in the right direction.  Not sure if it
needs to be paired with distorted pressure information.  As I understand it,
the spring is what sets the upper boost.  The control the ECU has is to help
the spring open via vacuum on the top of the wastegate as it detects the
boost going up in order to avoid overboost due to inherent hystereses in the
control system, and to feather the abruptness of the springs opening.  Some
systems have an ability to control the spring in the other direction, too,
by pulling on the wastegate diaphragm from "below" with vacuum, adding to
the spring's pressure.

Now to show my ignorance of the MC's system, I don't know if it uses vacuum
or pressure to influence the spring.  If pressure is being fed into the two
sides, the effect would be reversed from what I described for vacuum above.
One of these days I'll have to put some meters on the system so I can
understand it better.

In any case, try a softer spring, and try disabling the top or bottom vacuum
or pressure hoses on the wastegate to see what happens to your boost.

Best,

Bernard Littau
Woodinville, WA
'88 5ktq