Ducati 900 : FUEL INJECTION VERSUS CARBIES ( AND MORE VALVES ) (Updated)

Similar to the fuel injected 900 except for slightly smaller cams and Mikuni carbs, the carby engines make great lower RPM power that is accessible to any road rider.

The main difference you will see in the power curves is that the carb model stops making power at around 7,000 RPM. This is due, as far as we can tell, to the long inlet manifolds. Any mod to these engines then, must involve making the most of what is available under 7,000 RPM, or replacing the manifolds. Replacing the carbs while keeping the long manifolds will give an increase in performance and response equivalent to fitting a good jet kit to the standard carbs. For this reason, I haven’t yet replaced any carbs. Fitting shorter manifolds and some Dellortos or Keihns will give a similar performance potential to the fuel injected bike. Although they have drawbacks in terms of setting up for street use, particularly with regard to air filters and jetting. The standard carbs are a fantastic piece given what is expected of them.

The dyno chart below shows std power curves for a carb 900, a FI 900 and a 916. The carb engine (green) is better than the FI up to 7,000 RPM, more so on the road than the dyno would have you believe. From there, though, the FI engine (blue) takes over, pulling all the way into the rev limiter. The carb engine needs no rev limiter. Revving one of these engines to 9,000 RPM is very obviously a waste of time.

The third curve shown (red) is a 916, with the improvement afforded by more valves and water cooling very apparent.

(dyno graph courtesy of DYNOBIKE, (03) 9553 0018)

The dyno chart below shows the usual dialed cams and fueling mods made to all three. This closes the gaps to zero up to 6,000 RPM, a product of the fact all three that are approximately 900 cc and operating with good volumetric efficiency, regardless of their advertised compression ratio. It is interesting to note that the largest gains are made with the 2 valve engines, showing their unused potential in std form.

The differences above 6,000 RPM show the benefits to be gained from updating an engine design. Once again the curves are carb 900 ( green ), FI 900 ( blue ) and 916 ( red ).

(dyno graph courtesy of DYNOBIKE, (03) 9553 0018)

I’ve added the graph below to include a 916 SP. The bigger cams – G inlet, A exhaust really show their effect in this torque curve. These bikes really come on from 6,000 RPM onward, and you can see why. The more they accelerate, the more torque they make. Great fun when you can give them a handful of noise. Not so good down low, and not good if you’re wheelying without thinking. Even though the 916 Strada makes more torque for much of the rev range, the angle of the torque curve at the top end gives the rush that so many love. The lighter engine internals of the SP ( just like the 996 SPS ) contribute greatly to the acceleration potential of the bike. This gives the on road difference between the Strada/SP that most people incorrectly perceive to be difference in power output.

It also shows that the combination of light weight and lower range torque is what makes the 900 SS carb bikes so good to ride on a windy road. Plenty of grunt to pull you out of a corner, especially with the cam timing/jet kit/airbox mods. As yet I haven’t done a full before/after on one of these bikes with hi comp pistons, but that would make life in the real world even better.

Blue is carb SS, purple SS ie, green 916 Strada and red 916 SP. The SP is "out of the box", whereas the other three have cam timing and fueling mods ( plus airbox mods on SS models ).

(dyno graph courtesy of DYNOBIKE, (03) 9553 0018)

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