ST3 Base Runs, Etc - Written Nov ‘04
The new ST3 3 valve engine is the latest of the revised engine series. Same dimensions as the 1000 ds engine with a 3 valve head and water cooling gives us 4 (well, 5 1000ds, ST3, ST4S/S4R 996, 999 and 999R) 1000cc engines with varying configurations and states of tune. It revs higher than the 1000 ds engine to take advantage of its increased air flow potential and makes about 10 more Hp. To allow the higher revs (limited to about 9,800 RPM) the bike has different rods to the 1000 ds engine (limited to 8,500 RPM), but otherwise a very similar bottom end. I’d suspect apart from the timing shaft and alternator cover differences to allow for the water pump (all bolt on parts) they’d be identical. Although in this new age of non interchangeability Ducati are rejoicing in I could well be wrong. For ’05 models especially, as the ST3 and ST4S have wet clutches, with primary drive covers just like an 800 or 620. Unlike the ST2, which ran normal 2V ie 45mm throttle bodies, the ST3 runs ST4S 50mm throttle bodies. Meaning it’s somewhat simpler to make in terms of parts used per bike (and therefore cheaper) I guess. It does run the same old 40mm header size though, like the 1000 ds and ST2, instead of a more top end power friendly 45mm.
I took our demo to the dyno to see what it made. The graph below shows the 4 set ups I tested. Green is all std. Blue is with some mufflers (Arrow I had lying around) and the idle trimmer raised 20 points. Red is with an air filter kit added and the idle trimmer raised by 40 points. And finally yellow is with the same set up as the red curve but with the std ECU replaced by a Ducati Performance Power Kit ECU. This ECU was sent to us to try from an ST3 power kit, but it obviously didn’t work too well. I can give no explanation why.
When I fitted the mufflers I ran the bike with the same trimmer setting then started increasing it to see if more fuel helped. The next graph shows all std again in green. Blue is mufflers fitted and no idle trimmer change. Red is idle trimmer raised 10 points. Yellow is idle trimmer raised 20 points. As you can see there’s not a lot in it, but it does appear to like the extra fuel. As you can see from the air/fuel trace it’s not doing a great deal to the mixture however. Although, adding even 20 points has a significant effect on the idle mixture so it seems the ST3, like the 800SS/M, is a clear candidate for a replacement ECU. Not that fitting the mufflers has made a real difference to the air/fuel mixture, which surprises me a little given the gain in midrange.
Next I fitted an air filter kit and tried the same idle trimmer changes to see what happened. Red is mufflers and air filter kit without idle trimmer change. Green is trimmer raised 10 points, blue +20 points, yellow +30 points and pink +40 points. Adding 40 points is not at all practical in reality due to the effects it has on idle and low speed running however. Power is first, then air/fuel.
I expected the Ducati Performance kit ECU to fix the “lean with std ECU issue” but was sadly rather disappointed. I’m not sure if any of these kits have been fitted but I can’t imagine anyone being happy with the result. On the road at mid throttle roll ons the DP ECU is very nice, and in this trim it goes very close to taking the ‘easiest to wheelie’ title away from the Multistrada and Brutali. But go to full throttle and there’s a big hole under 7,000 RPM. Once over 7,000 it really comes on and revs clean and hard to the limiter. The power graph shows the hole, the air/fuel graph the why. Red is DP ECU, green is std ECU +40 points (see previous graph).
So, the less said about that the better really. Next we’ll compare the ST3 to its 1000cc mates, the 1000 ds and the ST4S. I only have one set of all std runs for each model, and they do vary a bit (as the 1000SS U59 report shows), but we’ll have to make do. The same three bikes will be used for all states of tune.
First up all std. Red is ST3, green is 1000SS ds, blue is ST4S. The advantage of more valve area is shown fairly clearly. I’m not really sure why the ST3 is fitted with two 34mm inlet valves where the ST4S has 36mm, but the ST4S has 4mm bigger bore for less shrouding and (more importantly) a bigger reputation to uphold. So maybe the ST3 is held back a little for that reason. The 1000SS ds has a single 45mm inlet valve for comparison. The ST3 also has 40mm headers not 45mm as the ST4S does, and I imagine that should be worth 3 or so at the top end too at this power level.
Next we fit some mufflers. Again, red is ST3, green is 1000SS ds and blue is ST4S. This tends to even things up at the bottom end, although the 2V engine still has a slight advantage.
Finally we add air filter kits to the mufflers. This didn’t help the ST3 as much as I’d expected, unlike the ST4S. It does smooth the curves out nicely however so it looks somewhat more impressive.
The torque curves for the above graph show each engine’s character a littler better. The 1000SS ds (green) has lots down low then falls away typical air flow limited engine. The ST3 has a very similar shaped curve that simply looks like it’s been moved to the right about 1,000 RPM. Maybe the top end is artificially restricted somewhat to stop it directly threatening the ST4S, but the lack of bottom end is a big odd. That doesn’t make a huge amount of sense to me, given the cam timing. Not that I’d complain. As delivered the ST3 has sensible gearing unlike the other two and is a very nice thing to ride in terms of low RPM smoothness and response nail it and it just starts pulling and keeps going until the limiter. Riding all 3 back to back with the same gearing would be interesting, excessive wheelies not withstanding.
As the new “budget” ST model, the ST3 is a little confusing. The appeal of the ST2 over ST4 and 4S was always lower purchase and running costs. The ST3 provides similar purchase price advantages, but we’re not too sure about the service cost advantages yet. Hopefully it’ll turn out to not consume a great deal more time than the ST2. Although they’ve certainly succeeded in the seemingly impossible task of making the fairing more annoying and time consuming to remove with the ‘04 model facelift. Truly inconceivable!
But it is a rather nice thing to ride. For ‘05 it’s even quieter too with the change from dry to wet clutch. Some (the traditionalists and purists) are calling this a backward step, but a clutch is a clutch to me and a quiet one even better. Depends how you see it. It’d be a nice engine for other models, but I really can’t see any that it would slot into to be a viable model in its own right. A water cooled SS is a contradiction of intent and there’s already two 1000cc Monsters. Who knows. There’s also been some revision of engine management and internal components as the ’05 ST3 idles much better than the ’04 and seems to be nicer at low RPM.
And also I’m told the new seats are a vast improvement over the old. Might have to sneak one off a floor stock bike and do a test on my ST2.