851 and 888 SP3, 4 and 5 Comparison - Written 10/07
Summary: A short comparison piece on the SP3, SP4 and SP5 that I’ve dyno’d. Mainly because the SP5 makes so much more Hp and I thought it might interest some.
We’ve had a few of each of the 851 and 888 SP series bikes through the shop over the years. Even a Tricolour Kit Superbike that is very much the same engine wise as the SP, SP2, SP3 and SP4 when fully kitted. Never seen a SP (’89) even in photos and I don’t know of any SP2 in Australia, but there’s quite a few of the others around. I’ve only ever dyno’d one each of the SP3, SP4 and SP5 though, and haven’t dynod the Tricolour Kit, so it’s a small sample group.
The SP5 I dyno’d didn’t have a RPM trace, so when I used it in the 955 report (http://www.moto-one.com.au/performance/955kitted748916.html) recently I made a spreadsheet up and converted the road speed to RPM using the rev limiter RPM as a reference. The SP3 and SP4 are both featured in other reports, so I exported the data from their respective dyno runs from the Winpep software into the SP5 spreadsheet and made a comparison graph.
I’d forgotten how much power the SP5 made compared to the others and the dyno graph compilation one of the Yahoo 815-888 list (http://autos.groups.yahoo.com/group/Ducati-851-888/) members is doing at the moment made me think this might make a good (and quick) report. For those who don’t know, I’m very into 851 - the square ’88 to ’91 models in particular. The round ’92 - 888 remodel I’m not as fond of.
A quick spec and set up comparison to start with. I’d played with cam timing on all of them, although the settings were fairly close to spec:
All run the same exhaust system 45mm headers into the normal Ducati stamped steel crossover and 50mm out of that into upswept mufflers. Termi alloy mufflers on SP3 and SP4, carbon on SP5.
The airbox on the SP5 is a little different it’s probably a bit smaller in volume from memory, but has shorter and more direct hoses leading into it. All have open lids above the filter. All have 50mm throttle bodies with dual injectors, although the SP5 has the later style with side flow injectors used from then up to the 996. They also have air bleeds, unlike the 851 style early throttle bodies the SP3 and SP4 share.
The SP5 has much more available injector flow than the SP3 and SP4 maybe as much as 50% - due to the green side flow injectors simply flowing more than the red end flow injectors. The SP3 and SP4 fuel maps are at their maximum pulse width value at 7 and 8,000 RPM in the std maps they need bigger injectors or more fuel pressure with any tuning pretty much. Something I found out after I’d done these two bikes. Although they both should have adjustable fuel pressure regulators as std fitment, so you can play there to some extent. Not sure about the SP5 regulator, I don’t recall.
So apart from the G inlet cams and 1mm bigger valves of the SP5, they’re very much the same. The peak power output is, however, not. I can only assume all 3 were unopened the SP4 was one owner, the others on their second, but all were allegedly internally std.
The graphs show the SP3 in blue, the SP4 in green and the SP5 in red. I didn’t control the SP3 run, so it wasn’t run into the limiter like that others. I don’t know why the SP3 is so much stronger than the SP4 in the midrange, given they’re the same thing. The top end advantage of the SP5 is very clear it just keeps on going. I’m told the G exhaust cams the Corsa cam from ’93 (or earlier even maybe) onward - help the top end even more. Power is first, then torque.
Check out the dyno graphs folder in the Yahoo 851-888 group photo gallery as well for more graphs.