748R

Something of a misunderstood model, the 748R came into being as a ’00 model with lots of engine mods, but an otherwise fairly std, Strada-ish chassis. As such, most seemed to consider it overpriced, especially as the Termi mufflers that came with the SPS models as an included part were now an extra cost option. Needless to say, we didn’t sell many.

Then came 2001, and an up-spec’d chassis (Ohlins everywhere and the flashest brakes around) that turned the 748R into something of a perceived bargain. We sold a heap of them. The problem was, however, that it was still a homologation special for World Supersport racing. As such, it wasn’t necessarily a motorcycle, more a collection of parts masquerading as a motorcycle that gave the basis required for what Ducati then wanted to race with. If you got a 748RS, the attempt at illusion was much less enthusiastic. It was fairly clear the 748RS looked like a motorcycle as that was the easiest way to ship all the bits required to make up a motorcycle in the std Ducati crate. It was expected that the new owners would pull it apart and reassemble it as a race bike, as you do.

This great looking bike with lots of hot bits then gave us a few problems. Not at all surprisingly, they all centred on idle and low speed running. Which just goes to reinforce a point I learnt a few years ago. You can make it go like stink, but if it can’t be tootled around the suburbs, you’re in trouble. A few owners understood what they’d bought and used them accordingly. Some understood what they’d bought and put up with minor irritation. Some weren’t at all happy. This makes warranty issues for us, ones that sometimes aren’t perceived by the factory to be all that important.

Ridden as intended, the 748R is one hell of a bike. Used as transport, it can leave a little to be desired. I heard rumour of one refund being given just to make a problem go away, so to speak. Because I didn’t get any to play with (just fix it fast warranty running issues) and I was in the middle of recovering from my crash, I didn’t get too far into things like map numbers, etc, like I normally like to. This meant it was a while before I saw any maps and formed any opinions of what may have been to blame.

So to some extent, I wasn’t really looking forward to getting into the 748R. Just in case I exaggerated the problems. I don’t need that sort of agro. But with the info from people like Doug Lofgren and Neil Spalding, whose Sigma Performance operation raced a 748RS, I started to work out a bit of a plan, and an idea of what to look out for.

This 748R came to us with a bit of a problem, diagnosed as an airbox half seal that wasn’t sitting where it should have been. This had lead to the engine getting a good dose of dirt, causing a distinct power loss. So, it had to come apart. A good opportunity for us to play with it. Although, the owner took some convincing before agreeing to spend some more money. In the end, it was a bit more than I anticipated (quoted) and we took a bit of a bath on it. Happens some times.

Given the heads had to come off, we got our head guys to have a bit of a look to see what sort of porting would be useful. Doug Lofgren had done a couple of 748R into 853 and 872, with impressive results, but this owner didn’t want to get that carried away. So, with some very helpful advice from Doug on what he’d found to work port wise, we set about some minor mods aimed at getting what we could for not too much outlay.

If you want to see what Doug did, and all his comments, check out
http://www.visi.com/~moperfserv/872cc.htm
http://www.visi.com/~moperfserv/853R.htm

For Neil Spalding’s articles, go to
http://www.sigmaperformance.com/

We were working to a much smaller budget here, but a couple of Doug’s ideas appealed to me. Add to that our usual cam dialling (not that I had any experience on what timing settings to use) and I figured there would be some good gains to be had. As this bike was sick when it came in it didn’t get dyno’d before (and I hadn’t dyno’d any others). So I didn’t have a before run to work off. The Dynobike dyno had seen two others, so I took a look at those runs to see what the std output was, and how the curve looked.

The first two graphs below show some indicative runs for the 748 series. Red is a 748R with the Termi 50mm half system and an Ultimap (FIM) chip, with the fuelling set for best power. Blue is a 748SPS with another Termi 50mm half system (std in the box from memory) and an Ultimap chip without fuelling mods ("as fitted"). Green is a 748Strada with Arrows 50mm half system and Ultimap chip (as fitted). Yellow is another 748Strada with Termi 45mm mufflers and Ultimap chip (as fitted). Whether or not the 748SPS would have made the same power as the R if it was revved to 11,500 RPM I don’t know, but I would expect it to at least touch 100 Hp. Power is first, then torque. You can see the 50mm half system inspired dip @ 5,000 RPM, most apparent on the blue SPS curve. We had one 784R owner pick this after having test ridden a std exhaust bike before purchasing his (which was fitted with the 50mm half kit at pre delivery). It took me a while to work out why.


Dynograph courtesy of DYNOBIKE (03) 9553 0018


Dynograph courtesy of DYNOBIKE (03) 9553 0018

The similarity of the 748R and SPS curves is quite surprising, with the variation in spec between them. The table below gives some of the changes. All use the same 88 X 61.5mm bore and stroke.

Model
Valve
sizes
Inlet
timing
Exhaust
timing
Inlet
duration
Exhaust
duration
Inlet
lift
Exhaust
lift
Throttle
size
Injector
style
748Strada
33/29
11/70
62/18
261
260
9.6
8.75
50
Normal
748SPS
33/29
44/72
74/44
296
298
10.85
9.0
50
Normal
748R
36/30
20/60
62/38
260
280
12.5
10.5
54
Shower
748RS
36/30
30/62
74/38
272
292
12.5
10.5
54
Shower

The 748R and SPS come from the opposite ends of the Ducati power theory. The R has the later short duration cams with lots of lift and big valves. The SPS has long duration cams and std size valves. The R has a much larger airbox and larger throttle bodies with shower injectors, as seen on the race 996 from ’99 onward. The SPS is very much a hotted up Strada, whereas the R is a re-think of how to make it go. Bottom end wise, both have Ti rods as std (the earlier 748SP didn’t), and are very similar otherwise. Except for the 748R’s slipper clutch, pretty much.

The SPS makes its power by extending the time available to get air in and exhaust out. The R makes the same power by moving more air in less time. Generally, if you can move enough air to make the required peak power with shorter duration cams, you’ll also make more mid range power. Although, for racing, the 748RS cams that replaced the std 748R cams are slightly longer duration on both, helping with some more top end. The std lift of the R cams is required for homologation, as the rules dictate cam timing can be changed, but maximum lift cannot. And they wanted lots of lift.

Back to the bike at hand
What we wanted to do was lift the power curve as much as possible. I don’t usually expect to be able to increase the power made at the very top end, but the porting we were doing to this one would achieve some top end increase in addition to the usual mid range improvements. So we were expecting more all thru the range, and with the usual cam timing changes, plus Doug’s tricks, I thought we might do pretty well.

The two ideas I stole from Doug were extending the inlet trumpets above the throttle blades and machining the bore of the throttle bodies below the blades. Doug had done quite a bit of experimenting with extended trumpets, and recommended we try 15 or so mm. I machined up some spacers that ended up being 17mm, and we fitted them. There is still plenty of room between the trumpet top and the shower injector mounting rail, but going too much further would maybe cause flow restrictions/unsteady flow between them. Interestingly enough, shorter inlet trumpets were listed as an optional part for the 748RS, for better high RPM power.

The throttle body bores below the throttle blades reduce quite sharply to 44mm, down from the 54mm throttle blades. This is an FIM specified restrictor for 750 twins racing in World Supersport. As this bike was never going to be used for restricted class racing, we removed the step from 54 to 44mm by running a taper cut from the bottom of the throttle bodies up to under the blades, ending just below the air bleed ports. Now the bore reduces from 54mm at the blades to approx 51mm at the bottom of the air bleed ports, and then tapers down to the original 44mm at the throttle body outlet. I should have taken a photo to illustrate this a bit better, but didn’t get around to it.

So, we went to the dyno with a 748R that had the following done:

  • Ported heads (not a great deal done)
  • Dialled cams
  • Extended inlet trumpets
  • Taper bored throttle body outlets
  • Exhaust header stub welds ground down

I had Duane make me a couple of chips that had a custom spark map – mainly a lot less timing at idle and just above, where the std map has 28 degrees minimum! I thought this may have been contributing to the problems with hot idle after riding for a while that has been a continuing complaint. First up I needed to get some idea of required fuelling mods – given the 748R’s engine nature, I was expecting quite a lot of variation in what was going to be required, and that the solution would require a custom chip from Duane. I wasn’t wrong. The graph below shows power variations with fuelling settings. The chip I started out with was an Ultimap UM241 with +10% across the whole fuel map and my custom spark map. The curves below are base fuel in red, +5.4% in green, +10% in blue, -5.4% in yellow, -10% in mauve, -15% in pink and -20% in aqua. As you can see, the fuel required for best power was changing from +10% to -20% in the space of 1,000 RPM in places. So, I did some part throttle air/fuel runs to see what that looked like, then did some riding around with the hand held terminal on the fuel tank trying out various part throttle settings, then put it all on paper to send to Duane for him to make us a custom chip. A good and sometimes frustrating way to waste a few hours.


Dynograph courtesy of DYNOBIKE (03) 9553 0018

Once we had the custom chip from Duane, we fitted that and headed back to the dyno for a check, and hopefully a nice "final" power curve. I always add about 5% to the "best dyno power" fuel settings for the road, so I ran the new chip as was, then subtracted 5.4% and 10% from the map for the final power runs. What we got is shown below.

Green is custom chip without any fuel mods, blue is map -5.4%, red is map -10%. You can see the kick right at the end with -10, something that is fairly normal with leaning the very top end mixture. The flat spot at 4,500 RPM is also very fuel sensitive – over richness there really kills the power. On the road, that flatness is hardly noticeable tho. Overall, the variation with a little less fuel is expected (as I specified the fuel map mods), and what I like to see for a custom chip.


Dynograph courtesy of DYNOBIKE (03) 9553 0018

How does it compare to a std 748R? Well, I don’t have any std runs for this bike, so I can’t give the definitive answer. The next graphs show a comparison with a 748R (the one shown in the initial comparison) from the files of the Dynobike computer. This bike is a 748R with a Termi 50mm half system and an Ultimap chip (same UM241) with the fueling set for best power. So basically the same as this bike was before we started. Red is our 748R, green the std-ish bike. In these graphs (power first, then torque), ours looks pretty good


Dynograph courtesy of DYNOBIKE (03) 9553 0018


Dynograph courtesy of DYNOBIKE (03) 9553 0018

There is another 748R on the dyno computer, although there is no RPM trace for this bike. So I’ll show them all against road speed. Red is our 748R, green is the same green run from the previous graphs and blue is another Termi 50mm half system/Ultimap chipped bike. Again, ours looks pretty good.


Dynograph courtesy of DYNOBIKE (03) 9553 0018

To show how the 748 compares to the 748Strada, I’ll show the next graph. The red line is this 748R. The two Strada's shown are from the cams dialled reports – blue is the bike with the 45mm Termi mufflers, green is the bike with the 50mm Arrow half system. The origin of the 74R’s flatness at 4,500 RPM is clear here – it’s the dip generated by the 50mm half system. How it would work with the 45mm Termi's is a question I doubt I’ll ever see an answer to, as every 748R we fitted an exhaust system to got the 50mm Termi "kit" that was seen as the gun set up. I thought showing this 748R with the two "played with" Strada’s was the fairest way of doing it. The upper RPM power of the 748R is fairly obvious – it feels that way on the road too.


Dynograph courtesy of DYNOBIKE (03) 9553 0018

So that’s our first take at a 748R. For a bike with such short duration inlet cams, the high RPM torque certainly impresses me. What is responsible for it, I’m not sure. I had heard others say that bigger exhaust cams (as a rule) seem to bring these engines to life at higher RPM. Maybe it’s just a combination of small capacity working well with the bigger valves, greater valve lift, throttles, etc. The extra 2,000 RPM that it holds its torque for before it starts to fall – 10,500 compared to 8,500 on most other Desmoquattro – is not that long, but in power producing terms it makes a huge difference.

I’d like to have a go at another one, this time without the porting. As we don’t usually pull heads without good reason, we don’t do much porting as a general rule. And the time added in stripping, reassembling and reshimming heads after porting, plus the cost of gaskets, makes the whole job rather expensive. Doing the cam timing, throttle boring and trumpet extending will be much cheaper. How much less we’d get I’m not sure.

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