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Desmo Due rules ....

What and Why ?

The Ducati's Sporting Club has decided to help organise a race series to allow those of its members currently doing track days to have the opportunity to race a Ducati based motorcycle at club level here in the UK. The concept is of a group of bikes somewhere just over 150 Kg and up to 70 bhp. It may not sound like big numbers but that's partly the point and it's plenty when all the opposition is on similar bikes. The idea is to focus people on everything else except power; there is a much bigger difference in lap times to come from a bike that has been set up well than from a few extra horsepower.

This is a look at the rules to see how they have been organised and to understand the logic behind them. On the technical section of our website there will shortly be an article showing a bike being built to these rules, this will include what we think are the most logical modifications to get the best performance.

The Desmo Due heading allows 600 and 620 Monsters; SS's and Multistrada's to compete against each other.  The rules limit the changes allowed and set out a series of permitted modifications that should allow the old 583 cc '600' engine to be modified sufficiently to keep up with the later motorcycles. The later Monster chassis is typically sold without the adjustment capability as the older one, but the later chassis can be modified to the same level of adjustability as the earlier one.

The basic assumption is that we have to allow modifications that maintain safety, encourage equality and allow owners of older and/or less well specified bikes to modify them to the point where they are all competitive with each other and where the bike with the highest original spec doesn't get a major, and unfair, leg up. Part of the fun of racing is the scheming and plotting in the off season so a few mod's are allowed to keep imaginations working without letting things go too far.

Lets look at the Chassis first ...

There are five basic chassis here ... the old Monster; the new Monster, old SS and new SS and the Multistrada.

All share some basic similarities in geometry. Sure they look different but if you put them all on a frame jig the main points are remarkably similar.  Fork length may be different, rear shock and swingarm design may be different, chassis height and bodywork are different.

With a little effort it is possible to make a bike that started out as Monster to handle like the Multistrada, and vice versa, same with old and new SS's. The rules legitimise most of the adjustments you will need to achieve these changes

The old 600 Monster uses a chassis with a familial resemblance to the old 851 and 888 Racing chassis. With the advent of the 620 Monsters Ducati switched to a chassis based on that first launched on the ST2 tourer back in 1997. This chassis is possibly the best that Ducati currently make.  It is capable of being adjusted to provide a slow and gentle steering motorcycle for touring, a low and domesticated motorcycle for the Monsters and once raised a quick steering sporty chassis for the Multistrada.

The reason for allowing in adjustability in the chassis section is so that the new chassis can be transformed from the 'low in seam variants' to the very quick steering and capable racing chassis that has always been hiding in there. All of the chassis (except possibly the Multistrada) will need raising in order for them to fall into corners better. Raising the centre of gravity in any motorcycle will let it tip in quicker and, given that a racing biker is not unduly concerned about how stable it feels at the traffic lights, we can afford to raise them a little. The trick, as ever, is not to do it too much.

The 600 Monster already has adjustable ride height with the ball end joints that connect the top of the swingarm to the linkage allowing the ride height to be raised and lowered. The 620 i.e. has a linkage identical to the ST2, however on all bar the top model of the range, no adjustment is available. The rules have been written to allow the fitting of adjustable ride height rods, which only cost about £100 so the chassis can be modified to be far more effective on a racetrack. The SS chassis would require a ride height adjuster to achieve the same aims, these can be added to after market shocks at very little cost.

The rear shocks on all these bikes have been very much built down to a price.  It makes sense to allow a higher quality of damper unit and for the valving inside the forks to be modified to a setting more likely to be needed on a racetrack. As none of Ducati's 600's has come with externally adjustable forks its safe to keep them out and insist that any changes are internal.. Believe me you can change a lot with different oil viscosities, oil levels, spring rates and preloads…cheaply.

Swingarm's can be fitted from any bike in the range, if you want a heavy single sider that's up to you, if you want a short Monster swingarm on a Multistrada that's alright too A lot of Monster owners have removed some or all of the rear frame rails for cosmetic purposes. That's allowed, and as an acknowledgement of possible race crash damage the rear sub frame of any of the bikes can be repaired or chopped up, you just have to stay in the original material. The main frame must remain unchanged, except for one strut that may need to be removed to allow two single carburettors on short manifolds to be fitted on the older bikes.

In an attempt to restrict costs discs have to be from any standard Ducati motorcycle but the Calipers must remain as on the original bike.  Brake pads can however be changed and there is a startlingly good selection of Brake Pads available. Master cylinders though are a different matter, at the risk of upsetting those in the company I think we would have to concede that some of the older bikes had brake systems that possibly were not the best on the planet, allowing the master cylinders to be changed for aftermarket units will mean that riders can tailor the brakes to their personal preference.

Restricting the wheels also to standard wheels means that the temptation to spend lots of money on super lightweight magnesium wheels has extinguished.

Now let's look at the engines ...

The early 600 Monster and SS actually displaced 583 cc. The engine is the final variant of the old Formula 2 motor developed by Ducati for the Pantah.  Tony Rutter took race variants of it to the Formula 2 World championship on several occasions; this is one of the reasons why the rules limit the class to motorcycles (and that will include engines!!) built since 1992, it wouldn't really do the class a lot of favours if someone did turn up with an ex Tony Rutter bike and disappear into the distance!!

We could allow cams and valve modification but then we need different limits for each type of bike, it's far better to have the same limitations. The 600 cam has a longer duration but smaller valves. The 620 have bigger valves but a shorter, more midrange friendly duration, and intake closing point.

We need to find a way though to allow the old engine to be modified to make sure that if it is being left behind on the straights, and in racing that can be as much a function of the rider's ability to come off a corner as it is of the bikes sheer power, it can be modified to do something about it. Ducati Performance sell a 674 cc big bore kit for the old engine (they call it a 680 but, hey lets not get too hung up on a short fall.), many of these kits are still available and are being sold at discount. This allows riders who don't want to spend too much money to do the first year running a basic 600 engine, work out how to make it handle and find their own limits, then take the bike up a level of performance but at a realistic cost allowing an additional 91 cc.

Increasing capacity this much will certainly make the old engine work far better, most Dyno charts show horsepower with nearly the same horsepower as an unmodified 620 engine but that's not the full story.  The power curve that results is midrange biased, so the question was; what mod can we allow to the bored out 600 that won't also benefit the 620? Now those Dyno charts reflect an engine where the original carburettors and long inlet tracts are left on the bike. The rules allow different length inlet manifolds and carburettors or throttle bodies to be fitted. This has been thought through as carefully as possible; we want a set of rules that will stand the test of time. 

To give you an idea of just how the game can be played have a look at these charts.  There are power and torque curves form three bikes here.. the red line is a 620 , the others are 750's,  the bikes have the same cams, valves and heads.  This little 620 is making the same power as an old carburetted 750. Funnily enough it displaces 20 % less and requires 20% more revs to make the same power.  The differences are in the bore and the size and length of the inlet system.

A graph showing that the 620 really is a shrunken 750, using revs to get up to the
same power levels as the old 750 carburetted engine
(Graph: Doug Lofgren)

So why are there such long inlets on the old Ducati?.. Its simply because when they were designed the factory needed to find and use a simple easily available pair of carburettors, it found the Yamaha TDM 850 had carbs of an acceptable size so a manifold that would let them fit was constructed and off they went. Because of all the flow restrictions inside them the 38mm CV carbs breathe like 34mm slide carbs, so 36 mil items would be an improvement.  Whether you are changing crabs or not changing the manifolds should help a bored 674cc engine move its power up the range.  The old 400 and 600's shared an inlet manifold design, the 750 and 900's shared another.. they all used the same carbs though. Using the 750/900 inlet manifolds should allow better high rpm breathing so, wile this might cost some midrange this could help out the top end.

The move to fuel injection has allowed a rethink; a set of big 45mm throttle bodies allowing a shorter inlet length was designed (its amazing what you can do when you are not worrying about what to do with the float bowls!!) and they are now fitted to the 620/800 and 1000 twin valve engines. It is extremely unlikely that replacing the standard throttle bodies on a 620 would result in more power, this section of the rule book therefore allows an almost completely 600 biased improvement.

In its favour the 620 has better drivability, and a much wider power band. The capacity rule means it can be bored to the same size but as it is starting at 620 you can only add 55cc. The rules are designed to allow the inveterate fiddlers a chance to build a quick 674, for the rest the easy way in is to buy a 620ie……

By the time we are halfway through the season I'll wager a modified manifold / carburettor 674cc kitted 600 will be making 62 is bhp and a properly built 621cc will be on the same…

Other stuff:

Slipper clutches.  Most of the 04 and on 620's have the APTC clutch as standard. Now this isn't strictly a slipper clutch. It is a clutch that is designed to transmit full power under acceleration but be light on clutch pull the rest of the time. That means that if there is a lot of wheel hop it will slip. For all the early 620's and all the 600's we need to allow a level playing field. There are a lot of Ducati slipper clutches around right now so either fitting an APTC fitting a modified air-cooled type clutch in side the oil cooled cases shouldn't be difficult.

Fuelling: On old bikes a Dynojet kit is all that is needed if you are keeping the standard carbs. If you are going for a pair of carbs the Dellorto's seem the least expensive type (they are only about £150 each), 36mm PHF ones will probably do just nicely, there again someone might squeeze on a pair of 39mm CR's. The bike it is easiest to make competitive is the basic 620 Monster, and that can make do with the standard computer with modified CO2 levels for most things. Any dealer can trim the CO2 with his Mathesis tester.  If you insist on more then there is the FIM Ultimap U59 computer or a Dynojet power commander.

Weight is a concern: A Multistrada is going to weigh more as long as it has that fuel tank on it, the day we do a race that need 24 litres it'll be interesting though!! The right minimum weight level is the lightest bike we can find in the range, that honour goes to the latest 620 single disc Monster Dark at 166kg, now that's Ducati's new 'dry' weight but we are going to allow, nay encourage, a few mod's but in the real world even when the lights, standard pipes and footrest mounts have been consigned to the circular file in the corner of the workshop 150KG wet is still going to be a challenge. We don't want them too light, it means we are getting confused about the definitions of cheap and racing, but if you can get it down to150kg (330lbs to those still on imperial.measures), that'll be a pretty good effort.

Undertrays: For racing you just got to have them.  Its not even if you dump oil on your own back wheel and crash, it's a matter of respect elsewhere to fit them so no-one has to race on a track covered in cement dust as a result of our class….Sigma are making a production run of oil containing undertray's to fit all the unfaired bikes.

Rider eligibility: This class is about going racing in a competitive group without having to deal with the axe murderers of the 600 Supersport class…insisting on all competitors having a full licence for at least 2 years will at least keep out the youngsters trying to become world champions. It won't stop faster riders deciding to give it a try but they have to build a bike first.

Summary: A race series that allows inveterate fiddlers to play with older cheaper bikes and keep up, that allows Ducati enthusiasts to have a race Ducati in the garage and not go broke, that encourages riders to understand bike setup and which provides the right environment for the best fun you can have with your clothes on …..

Copyright Neil Spalding 2005

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