SM4 Manual
by
MRM-Racing
V3.0
30
Full power zone:
This is where the engine produce top power, and the fuelling is set very rich to avoid heat
buildup and irregular combustion. Setting it to rich may give the same problems as when
setting it to lean.
This is where we put the big effort on the dyno to get the last of the lazy horsies to pull.
Power transient zone:
Here we will end up when gear shifting after being in the full power zone. We can also
end up here when the throttle is temporarily lifted. Fuelling here is leaner than on top
boost, but there is no use in getting to lean here, since the engine and tubo internals
have lots of heat built up. This zone managed the heat buildup when we lower the
exhaust flow suddenly by letting go of the throttle.
Care must also be taken for the case that we temporarily lift the throttle, and then go
bank on full bost again. If to lean here, the engine will at first get way lean and hot when
it gets back to the full power zone.
Overrun deceleration zone:
This zone is where the engine is transient in and out of overrun. Using overrun fuel shut
off on a high power turbo engine is nearly a must, since high rpm overrun is the place
where EGT can rise dramatically. Either the engine must have fuel cut off, or being rather
rich fuelled. Care must also be taken for large injectors not being able to fuel properly
with small injector openings on the vaccum line.
Coasting zone:
This zone manages fuelling when we are coasting. On a street engine we want to keep
this lean because of emissions and fuel economy. But on a race engine we want this to
be fuelled for best driveability without heat buildup, and without filling the engine up with
sot.
The forbidden zone:
This is where we never should be able to end up. We are well below the turbo spoolup
rpm's.
But still, we can end up here after selecting the wrong gear in a power shifting with boost
pressure.
Of different reasons, the turbulence in combustion and flow through the engine is low in
this area, and here is where most modern petrol engines are most prone to knock. So
this cell must be properly fuelled so the engine does not get damaged if we happen to
end up here.
(The ignition table at these load sites should be set rather low).
