THE MAN BEHIND THE REVOLUTION
Luca Bandiera was the man charged with making the V4R’s masterpiece motor a reality. It was only right that we gave him a good grilling on revs.
FB: What are the main differences between the V4R and V4S 1103cc motor?
LB: The differences are cylinder heads, intake and exhaust valves, pistons, conrods, camshaft, crankshaft, clutch (dry on the 998 version), air intake diameter.
FB: Is the 998cc closer to the MotoGP engine, or more a
998cc version of the V4S engine?
LB: Both engines are MotoGP inspired. The 998 is one step forward to the MotoGP Engine.
FB: Are the V4R pistons forged? Is special aluminium used? Are there any friction coatings on the skirt?
LB: The pistons are forged. The high-strength aluminium is the same on the 1103 version. There is no friction coatings on the skirt.
FB: Why did you decide to use just two piston rings? Is there any special design or material used for the piston rings? Is there more oil consumption with two rings?
LB: The 1103 has two compression rings, plus one for the oil. The 998 has one compression ring, plus one special oil ring, specifically designed to reduce friction. The reduced friction is the driven for many parts of the 998 engine. Oil consumption is within acceptance limits.
FB: Is the head and combustion chamber design similar to 1103 engine? Any mods needed to improve burn at peak revs? Squish, etc?
LB: The combustion chamber design is the same for both engines. This is designed around the bore of 81 mm, the same of both engines and the same of the MotoGP engine, where we have a lot of experience.
FB: Are the spark plugs unusual?
LB: Yes, but only for dimensions. On both engines we use special spark plugs with a smaller dimension. This helped us also to build compact engine heads.
FB: With the valve timing, has desmo helped with the potential for high rpm? Would a 998cc engine at 15,500rpm-plus be possible with conventional valves? LB: On the 998 engine we have the rev limiter (on 6th gear) at 16.500 rpm. This is possible only because of the Desmo. We are the only manufacturer that use the same distribution of the MotoGP Engine. Other MotoGP manufacturers use pneumatic valves to reach that level of rpm.
FB: Why exhaust valves not titanium? LB: Because it was not necessary to use it. Also because the save of weight was not so big.
FB: How many more revs can the engine take; i.e., what will be the rev limits in race trim?
LB: The WSBK allows only a few rpm more than the road bike. There is a complicated formula to calculate it that for our engine is more or less 200/300 rpm higher.
FB: What is the potential power in race trim, roughly?
LB: Sorry, but this is our racing secret!
combustions per second, in each cylinder. And the piston makes the journey up and down the cylinder 550 times each second. So there’s 1/550th of a second to fill the cylinder with fuel and air.
Okay, air can be moved fast, and big ports and valves, large throttle bodies, carefullysized inlet trumpets, cunning exhaust systems all help here. There’s a downside to all this, though. Big ports and valves work less well at low speeds, so what you gain up top you can lose down low if you’re not careful. Having 220bhp at the top end of a race engine is no good if your competitors are making 50bhp more through the midrange, when you’re pulling out of a hairpin bend. Just making an engine breathe efficiently at super-high revs is difficult enough, but the next enemy is a mechanical one – maximum piston speed. As we pointed out earlier, at high revs the piston moves up and down the bore a lot. There comes a point where the speed gets so high, that normal aluminium can’t hold up any more. The forces on the rings, and the friction created by the high speed is bad enough, but you also need to cope with the massive forces at top and bottom dead centre, when the piston and rod have to be stopped, then started moving again in the other direction.
Maxing out
How fast does a piston move, then?
We work out the *average* speed of the piston by a fairly simple equation
– average piston speed = 2 x stroke x (RPM60). If you’ve got a spare ten minutes on Excel, you can work out the piston speeds for some engines, and you’ll quickly see the current limits. On a basic commuter engine like a Honda CB500, which makes peak power at just 8,600rpm, with a stroke of 66.8mm, the average piston speed at peak power is 19.15m/s. The 2019 S1000 RR makes peak power at 13,500rpm with a stroke of 49.7mm, and at that point its piston speed is 22.36m/s. At the redline of 14,600rpm though, the little Bavarian pistons are whistling along at 24.18m/s. The V4S pistons move at 25.85m/s at its 14,500rpm redline, while the new V4R pushes this up to 26.62m/s at the 16,500rpm top-gear redline. Erk.
This explains why the Panigale V4R piston is such an advanced design. Ducati’s used a two-ring forged design rather than the three piston rings used on normal road engines (the only 4-stroke production bike on the market that goes down this route).
A three-ring design uses two compression rings and one oil scraper ring, but the V4R has just one compression ring and one oil ring to cut friction. It’s a bold step, and with one less ring, you might expect more in the way of oil consumption.
Ducati has a load of experience here, of course – its big twin superbikes had to make massive pistons move at big speeds – the 1299 Panigale’s soup-bowl pistons were hitting 25.6m/s at 11,500rpm. The 1199 Panigale R revved 500rpm higher: its pistons were doing a stunning 26.72m/s at the 12,000rpm redline – the highest piston speed we can find in a ‘road’ bike. Therefore, making smaller pistons that can hold together at these speeds is well within the Bologna
skill set. The final problem with high revs is the valves. Remember that while the crank spins once per engine revolution, the camshafts rotate twice as fast, and the valves have to open and close in a vanishingly small period of time at high revs. As we worked out earlier, at 16,500rpm, there’s 1/550th of a second for an intake and exhaust stroke, so the intake valves have to open fully, let the charge into the motor, then close again, sealing in the massive combustion pressures in around that time period. Then the exhaust valves have to open and let the red-hot gasses out again in the same kind of time. With conventional engine designs, the valve springs need to be very strong and stiff to bang the valves closed in time, which adds friction. There’s a big advantage in cutting weight here, of course, because lighter parts can be accelerated and decelerated much faster, and the forces involved are smaller, so you can use lighter springs. Ducati uses titanium inlet valves and titanium valve retainer collets to cut mass, although the (smaller) exhaust valves are steel, because the weight saving wasn’t worth the effort.
Get the valve control wrong, and the valves can start to ‘float’ – staying open a fraction longer than desired, and that’s when the pistons can hit the valves, wrecking the motor. Ducati has a big advantage here. Its desmodromic valve operation lets it use radical cam profiles, big valves, and high revs, because its engines use two cam profiles for each valve, one to open the valve and one to positively close it again. Using a mechanical cam to slam a valve closed rather than a spring means more exact valve movements, which is a massive benefit at high revs. So, in the end, maybe it’s not such a big surprise that Ducati is able to do this. It’s been working for years with massive piston speeds on its big-twin superbikes, and its decades of experience with desmodromic valves lets it apply that technology to the problem, too. Add in the closeness of the MotoGP Desmosedici engine design to the Panigale V4 motor, and perhaps we shouldn’t be so gobsmacked, disconcerted, or dumbfounded at the V4R’s power and revs at all.