Ducati 748 STRADA - Written 02/02, Updated 09/02, 03/08

Finally someone brought me a 748 to play with. I wasn’t really sure of what sort of result I’d get, so I told the owner exactly that. Didn’t put him off.

This bike had an ARROW 50mm half system – mufflers and collector – fitted, of which I wasn’t sure what effect this would have. The first graph below shows this bike against some others with mufflers/chips fitted. Just a baseline comparison to make sure this one was representative. It’s the green line.

Dynograph courtesy of DYNOBIKE (03) 9553 0018

The next issue was working out where to put the cams. The trade off would be pulling up the midrange versus keeping the top end. The 94 Hp surprised me I must say, but then I’d never dynod a 748 before. Given that the 851 only makes 93 I was a little jealous. Anyway, I checked how much piston to valve clearance I had to play with first up, and left a little margin for consistency between bikes if I get to do this again. The answer I got was somewhere near the settings I use for 996, so that was as good a starting point as any. I was just a little worried about whether I would lose any top end. I didn’t really want to pull it apart again to try another setting, so I was hoping pretty hard.

Off we went to the dyno. We needed some more fuel, as expected. The shape of the curve was what I wanted to see most, and wasn’t disappointed. There was no more top end, but I don’t really expect that from just cam timing changes. The fact there was no less was a real bonus. The power curve below shows the improvement. The drop off over 11,000 RPM is mainly mixture related. Leaning the mixture here would reduce the difference, but I really don’t see the point for such a minor part of the rev range. Before is green, after is red. The torque curve below the power curve shows what you feel when riding. Up to 15% more torque, giving lots more midrange flexibility and general acceleration. The top end rush is reduced slightly, but starts much earlier.

Dynograph courtesy of DYNOBIKE (03) 9553 0018

Dynograph courtesy of DYNOBIKE (03) 9553 0018

A great all round result that was better than I could have hoped for. The bike is now much nicer to ride around in an everyday sense, with more general go. Very smooth still, which has always been an attraction of the 748/750 engine size. It should also be better for track use, giving much more acceleration out of corners and onto the top end.

Update 09/02

I got to do another 748 recently, the result of which is also posted in the 45 – 50mm exhaust report. This one differed in two ways – it had Termi 45mm slip on mufflers and some over trumpet air filters. The torque curve below shows the difference. The red and green are from the graph above. The blue line is the other 748. The smaller exhaust/muffler combo really pulls up the bottom end - @ 5,000 RPM that’s nearly 20% more. On the road you feel it as a long, flat torque curve. Some mightn’t like it because it loses the 748’s traditional top end rush, but if you want to go fast, this is where it’s at. The top end loss may be due to the filters, but I didn’t get to try that out. This bike had carbon air runners anyway, so this is the best filter option.

Dynograph courtesy of DYNOBIKE (03) 9553 0018

Update 03/08

I wasn’t sure how representative the above graph was, but it’s been about 5 years since the last one before we got to do another 748 cam timing job (obviously not many local 748 owners are interested) so I haven’t had much of a sample group.  The next one was done with the same 108/108 timing, and fitted with the same 45mm Termi mufflers and Ultimap UM211 eprom that seems to work very nicely.  We dynod it before the mods and it seemed a touch rich and then after.  Some of the graphs I’ll show are spreadsheet generated which allows me to manipulate the data to show tuning based improvements as I’ll explain.

To the first graph of this report I’ll add the baseline run for this bike in pink.  As you can see, it’s a strong 748.  Whups the others anyway, by a fair amount.

The next graph is the power and air/fuel for this bike before we played with it.  The air/fuel is a fairly flat 12:1, a touch on the rich side.

Next is before and after power and then torque and air/fuel.  Before green, after red.  The after run shown has no fuelling changes, which shows the influence of the revised cam timing alone on the fuelling.  The cam timing was set to our usual for Strada cam 4V motors 108/108 centrelines.  From memory I moved the inlets 14 and 16 degrees using offset keys.  The exhaust I don’t recall.

As you can see it’s quite a bit leaner at lower RPM, because it’s trapping quite a bit more air.  I ran a set of +/- runs as I usually do to see what fuelling it liked best, going up to +20% and down to -10% in this instance.  These runs are shown below, just to give you an idea of what the variation looks like.  Power first, then air/fuel.

As this bike was a bit rich to start with in terms of best dyno power, and I know that leaning it out as it was would have made more peak power, the next graph shows the before compared with two after runs.  One being best power and the other equivalent air/fuel ratio - equivalent air/fuel ratio meaning that the power figures given at each RPM point are with the same air/fuel ratio as the before run.  This removes any improvements based on the air/fuel tuning alone which would make the result look unrepresentatively better than it is.  The difference is only slight and mainly over 10,000 RPM.  But it’s just to make it a true before and after comparison.  Green is before, red best after power, blue equivalent air/fuel ratio power.

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