Chef
Changing gearing does not change any of the fuelling parameters, it does however change where things take place.
Because your fuel Inj system has an rpm sensor within its monitoring equipment, it will tell the cpu how fast the engine is turning, and how much fuel to squirt in to the cylinders.
The amount of fuel squirted into the cylinders is also determined by signlas from the air press sensor and the TPS (throttle position sensor), and others.
Changing your gearing does this :-
Lets say you are riding along in 4th gear doing 50 mph, then your engine rpm may be 4000 rpm, all this done on standard gearing. (Figures are only theoretical)
If we go and drop a tooth on the front cog and travel along in the same gear, at the same speed, then the engine must turn faster to produce this speed (engine rpm will increase by approx 6% - if you need me to tell you how I get this figure let me know). This means that the engine will now turn at approx 4240 rpm.
Therefore the fuel injection system may be telling the injectors to squirt a different amount of fuel into the cylinders, than it would be on standard gearing. The amount of fuel it will squirt is taken from the fuel map (either the original eprom, or that from the power commander).
This basically means that you are operating your engine in a different rpm range.
It is possible to get a piggy back fuel injection controller which can adjust fuel ratios on the move, but these cost about 400 – 600 quid, and to be honest you don’t need them.
The FIM eproms tend to be the best aftermarket chips, as they have individual cylinder maps, thus compensating for the differing heat states of the cylinder (the rear cylinder runs slightly hotter than the from one, as it does not get the same air flow as the front one).
Ducati’s original chip brings the rear cylinder fuel quite lean at times, and this can be dangerous if a fault arises, it can destroy engine components, that’s why people change the chip, for aftermarket ones.
One other area which is quite a simple tuning mod is a lightened flywheel, but this does have an effect on engine performance. –
A lightened flywheel reduces the inertia exerted on the engine as it tries to spin up to a faster speed, but due to its increased momentum, keeps the engine at that rpm slightly longer when you close the throttle, before slowing down.
A lightened flywheel allows your engine to spin up faster, but also gives better response.
Due to the fact that you have lightened the flywheel, this reduces the amount of stored kinetic energy, and in the lower gears has the effect of “ reducing the mass of your bike” giving better acceleration.
You may not notice this when riding because bike clutches/flywheel assemblies are so small anyway, but it does happen.
There are other posts on this site regarding engine breaking effects of flywheels, but here’s what happens :-
Lets talk about the engine breaking produced by the cylinder firstly. This does not change, but is affected by the energy created/stored, and lost by the flywheel.
A heavier flywheel will pull engine rpm down quicker than a lighter one.
When you fit a lighter flywheel it “appears” that you have more engine breaking, but you simply take longer to lose the rpm of the engine, and thus the breaking forces remain longer.
Lightened flywheels require that you rev the engine a little harder to keep it at a certain rpm, or even to pull away from a stationary position.
I guess that’s it for now….any more questions ?
