MotoGP is the last bastion of what purists consider proper race engine technology. No forced induction, no electrical assistance. Here are naturally aspirated 1.0 litre four-strokes, either V4 or I4, DOHC, screaming to over 18,000 rpm and exploiting pneumatic or desmodromic valve control.
Action at the French Grand Prix with, to the fore (left to right) #72 Marco Bezzecchi and #73 Alex Marquez, both on Ducati, and #33 Brad Binder on KTM. Bezzecchi came through to win (Courtesy of KTM)
Only Yamaha uses an I4, only Ducati desmo; Honda, Aprilia and KTM have air spring V4s. These compact water-cooled jewels are restricted to an 81 mm maximum bore and a maximum of four valves per cylinder. Otherwise, restrictions are few, aside from a maximum fuel pressure of 10 bar, which rules out direct injection, plus there are curbs on what are judged exotic materials.
A limit on engines per rider over a season calls for a mileage of about 2000 km. There is a fuel limit of 22 litres for each Grand Prix. The electronics are a spec system provided by Marelli but software can be created by the manufacturer. All engines have to be frozen to a specification homologated for the season but, crucially, they can be developed from one year to the next.
To learn more about the state of the art in MotoGP engine technology, RET went to the French Grand Prix in May, roundfive of the 2023 season. Andrew Harrison spoke in depth to key engineers from Aprilia and KTM.
Aprilia
Romano Albesiano
Aprilia Racing technical director
Aprilia has a two-bike factory team and supports the two-bike RNF satellite team. The company started its current RS-GP MotoGP project in 2016 using a 72o V4, then in 2020 it introduced the current 90o V4. Aprilia Racing’s technical director Romano Albesiano said, “We switched because 90o is more of a fit to the MotoGP rules, let’s say.” The Aprilia engine department is headed by Walter Scattolin. Albesiano commented, “We have some really experienced guys there; they started with the [2002-4] Aprilia three-cylinder MotoGP engine. That Cosworth [codesigned] engine was, so to speak, the school for many of them, and then in Superbike and then back in MotoGP again.”
Maverick Vinales on the Aprilia at Le Mans 2023 (Courtesy of Aprilia)
Albesiano reported that Aprilia’s engine department employs about 20 people. At race weekends there is one engineer dedicated to “monitoring and managing everything regarding the engine for all four bikes. Plus we have two mechanics, one for the factory team and one for the satellite team. They are mostly dedicated to the transmissions – more so than the engines because you cannot do anything to the engine other than make many kinds of inspections.”
Aprilia’s fuel and oil partner is Castrol/ BP. In terms of engine development partners, Albesiano remarked, “We don’t have a partner in terms of engineering; our suppliers are our partners. So the piston supplier, the con rod supplier, the casting supplier and so on. But there’s no external engineering department we rely on, it’s 100% internal.”
The Aprilia V4
We asked Albesiano: how does your engine this year compare to the [power benchmark] Ducati? “Of course, we don’t know their numbers,” he replied. “But I noticed that on the very long straights in Austin, we had very good top speed. That’s affected by aero though, so it’s difficult to say. I can say that our riders definitely don’t complain about power. They’re quite satisfied with our power level.”
For Aprilia, this is the first year without so-called ‘concessions’. That means without permission to use a couple more engines per rider for the season and without being permitted in-season engine development and additional testing.
Albesiano said, “It’s not a big change, because last year we had the possibility to implement engine evolution during the season, but we did only really small things.” We asked: have you revised much from your engine last year,? “I think we have reached the level with this engine that it’s difficult to make big steps, especially from the volumetric efficiency side,” replied Albesiano.
“So we’re very much focused on friction reduction. And of course we still try to get the best with the intake and exhaust – we’re working a lot in these areas. But the engine itself, it’s evolving but only in small steps. If you put many small steps together though you get something good.
“Year by year, there is the fight for more revs. That is difficult, expensive and risky but it pays in terms of performance.” We asked Albesiano: what sort of rev limiter do current MotoGP engines have? “It is well over 18,000 rpm.” Do any engines run up to 19,000? “This is probably the target for many manufacturers.” What do you consider the current strengths and weaknesses of your engine? “I don’t think we have any real weak points. When riders come to us from other manufacturers, they are all really happy with the torque delivery, the power and so on. So I think our engine is a good one.”
Tightly packaged: the 2023 Aprilia RS-GP V4 (Courtesy of Aprilia)
What is the typical operating rpm range? “On some corners we go down close to 6000 rpm, so from there to more than 18,000. It’s quite a wide range. But you exploit the [full] power of your engine only above a certain rpm level because the bike is limited by grip in corners; by wheelies after. So the search for bottom-end torque we made in the past, we found was not a good way to develop the engine. Now we are more focused on top-end power.”
Asked if the power requirement to be competitive today is as much as 300 bhp, Albesiano replied, “If we talk in terms of the power at the crankshaft then that is the range.” And peak torque is something like 120 Nm? “Generally speaking, it is in that range.”
In terms of fuel and oil, Albesiano remarked that working with BP and Castrol, “I think we have reached a very good level. Next year, we have to use a 40% non-fossil fuel. We are developing that with our partner, and it is not affecting the engine design very much.” How significant is oil development? “Very important. You can get good advantage and reliability from it.”
Engine technology
Albesiano confirmed that Aprilia uses variable-length intakes, and said of their pros and cons, “I see all the pros except the complication!” Clearly this helps with the driveability? “Yes, even though we’re not looking too much to increase the bottom end, without variable-length intakes you will end up with very poor bottom-end torque.”
We asked Albesiano if pre-chamber combustion technology is relevant. “We have been considering this technology but we don’t see a real need for it, and we also see the difficulties of developing it without direct injection.”
What are your views on Big Bang firing? “I saw it first in 1992 when Honda came with it. Everybody said ‘What’s happening there?’ And then everybody did the Big Bang. But with modern electronics and the current four-strokes, I honestly think there’s not much sensitivity in this parameter.
“We have never made one engine as a screamer and a Big Bang [by way of comparison]. We never did so because it’s super-complicated, super-expensive. But my feeling is that it’s not a supercritical parameter. So at the moment with this kind of engine, the electronics, these flywheels, it is not something to worry too much about.”
How about counter-rotating crankshafts? “It’s something every manufacturer is using now. We did a lot of simulation when we decided to build our first MotoGP engine for 2016, and ended up deciding to make a counterrotating crankshaft. I would have liked to have been in a position to do the physical test of the two configurations but that was impossible.”
So you think it helps with the handling? “That’s the only reason for it. You lose 2% efficiency in having one more pair of gears.” Is steel piston technology used in MotoGP? “We are using a classic aluminium piston. I don’t know if someone else is using steel but I don’t think anybody’s using something different.” What are the current areas of materials development? “Coatings are the real matter. We are continuously testing different coatings on every part. Coating and finishing are the key.”
On track
We asked Albesiano: since last season, you’ve been exploiting a type of ground-effect aero; has this affected your engine development? “No. There’s no connection between engine development and this kind of aero development at this point.” Did it have an impact on cooling? “The aero design is affecting the vehicle temperature in the rear part of the motorcycle. But the engine’s working temperature – oil and water – are not affected.” Has the cooling requirement changed from last year for any reason? “We made a step from 2022 to ’23 in water temperature, and now we are more or less okay [in that respect].”
Can you give examples of fuel-saving strategies you would use during a race? “We are not struggling too much on any circuit with 22 litres. Sometimes in the most difficult circuits, we just run the engine leaner and instruct the rider to do short shifting where it’s not penalising performance. More or less, that’s what we need; no more [than that].”
Compared to last year, how easy is it to arrive at a circuit and get the bike dialled in? “Year by year, the range of changes we do when we arrive on track is reducing. Especially with Aleix [Espargaro] who has been riding with us since 2017. He has found his way, and the modification we do on his bike is quite small; I would say it is immediately very fast. “Maverick [Vinales] has been on our bike for a much shorter time. But he is doing the same processing: converging on a very good set-up, so we are not changing [his bike] too much. And with the current [event] schedule we are very limited in the range of experiments we can do. So you have to stay more or less on the same [set-up].”
KTM
Kurt Trieb
Head of engine, KTM Motorsports
KTM has a factory team running two bikes (three on occasion) and the two=bike GasGas factory team operated by the Tech3 team. Sebastian Risse is the technical manager at KTM MotoGP, and Kurt Trieb is the head of engine at KTM Motorsports.
KTM introduced its current RC16 engine in 2017; it is an 86o V4. Trieb reports that his engine group is “a team of nine designers and seven development engineers as well as nine mechanics.” For events, he commented, “In comparison to the chassis, you could say the engine is a black box delivered to the racetrack.
“We have one guy there who looks after all the engines, monitors the mileage and documents any problems. He has the overview of what’s happening on track. He is in close communication with my colleague who is responsible for operation and tests, and also with me.” In the GasGas factory team operated by Tech3, “they have quite a few people from our side. Including this year, with Pol Espargaro, crew chief Paul Trevathan; he is our guy.
“Then there is a guy who takes care of gearboxes and clutches, and if there is an engine issue, he connects with our guy at the KTM factory team.” For fuel and oil, as of this year the factory team is working with ExxonMobil. The GasGas factory team operated by Tech3, however, uses TotalEnergies. In terms of engine development partners, Trieb noted, “The engine is our own development. We have Pankl as part of our group of companies so of course we have close cooperation with them in regards of crank drive components including pistons and con rods.
“For those components, we do the first layout to sort out the package and what’s feasible. Then they do the FEM calculation and deliver the parts, we perform the tests and define the next development steps. It is an ongoing development process and cooperation.” Ahead of this season, KTM hired a number of engineers from Ducati. What has the impact of that been on engine development? “On the engine side there’s an exchange of knowledge and an exchange of experience”, Trieb replied. “So we have ongoing discussions about how to improve and what to improve. However, I see much more impact on the electronic strategy side – let’s say in the control systems, on track and in the factory.”
The KTM V4
Trieb said that in recent years KTM has tried “five or six different firing orders, and now we are quite happy with the configuration we have. I think we have always had a reasonably good and reliable engine. Reasonably powerful. “So this year the engine is not so different. But how it’s working on track is completely different. That’s due to, let’s say, a new set- up of the bike, new aerodynamics and new electronics strategies.”
It has been reported that this year KTM has made a step not so much in horsepower but in the feeling that the rider has. Is that correct? “Yes, the riders’ comments have been positive, from the beginning of this season when we introduced the new firing order,” Trieb said. “But I think that goes with our other changes, in electronics strategies and aerodynamics, and also bike set-up. So I think the whole package now works better.” There are also reports of you having better throttle response this year, are they true? “When we test engines on the dyno, throttle response is for us mainly how the combustion is at very low throttle openings; we couldn’t see a big difference. But the riders have reported some better throttle connection.
“My personal opinion is that, if the four cylinders work individually as four single-cylinders, then the better you can control engine reactions; the rider can control it better and also the electronics can control it better too. That’s my interpretation.” How do you compare to Ducati horsepower now? “I don’t know what top-end power Ducati has. But I think the step we made from last year has been a good one. “I think all the engines are now at a very good level, and to make something like a 10 PS increase is rather unrealistic. Steps are in the area of 1 or 2%. So for our step, we are talking about 3-5 PS.” What do you consider to be the current strengths and weaknesses of your engine? “I think the biggest strength is that it’s quite balanced. Good reliability, reasonable power. And also driveability; I think that’s at a good level.
“Perhaps we are not outstanding in terms of top-end power but we are close. Perhaps we do not have the smoothest engine but it is smooth enough to be controllable. So I think overall it’s a good package.” What’s the scope for ongoing performance development? “Of course, another step up in top-end power, that’s always a target. Then reducing the weight and improving the package, making the engine ready for a higher engine speed, which is always quite a challenge. Fuel consumption as well of course, that’s becoming more and more important.”
KTM displayed its 2020 RC16 engine at a special exhibition in the KTM Motohall in Mattighofen, Germany (Courtesy of KTM)
What rpm are MotoGP engines generally running to? “I think the V4s are running at something between 18,000 and 19,000 rpm. The Yamaha I4 is probably a bit less.” Do you know if any run over 19,000? “Perhaps Ducati in qualifying.” What’s the typical operating speed range? “We have occasions when the speed drops to 5000 rpm, but that’s rare. In general, I think it’s from 9000 rpm, and then above 14,000 rpm and in higher gears you can apply full power.”
At 5000 rpm do you still have good driveability? “Yes, no problem. I think that’s an important difference from Formula One engines, at least the naturally aspirated ones from the recent past, which were working above maybe 12,000. This is a significant difference to our MotoGP engines.”
In MotoGP these days do you need at least 300 bhp to be competitive? “It depends on how you measure the power on the engine dyno and if you apply overpressure from the airbox as a standard measurement method. “We measure our power at ambient pressure, and I would say 290 bhp is a good figure. If you also consider overpressure in the airbox at the end of a straight, then you do arrive at 300 bhp.”
Front wheel off the ground – Brad Binder in action at Le Mans (courtesy of KTM)
And the current peak torque in MotoGP is about 120 Nm? “120 is a good figure.” Have you started work with next year’s 40% non-fossil origin fuel? “We have already tested some of it, and the difference is not that significant. Going to 100% non-fossil in the future is another step, and I think some more [engine] development will be required then.” So the 40% can be considered a drop-in replacement fuel? “Yes.” How significant is oil development? “Having a new partner this year was good for us. They brought some test products, which were very interesting.
“We are running just one oil circuit for the engine and gearbox. So if for instance you try to reduce the friction in the bearings using thin oil, you get problems in the gearbox. So oil development is important and is always a bit of a balance.”
Engine technology
We asked Trieb: do you use variable-length intakes? “We use a very easy system, whereby we can switch between two intake lengths. The reason for going with that was simply reliability and to reduce complexity and weight. “We use it just to smooth the power curve. Below 14,000 you cut the power anyway using the traction control; above that, the base engine has to perform well and we use the variable trumpets to do some slight tuning. That’s our main target for the variable intake.”
Is pre-chamber combustion relevant? “MotoGP has to go towards sustainability, so fuel consumption is a topic. As far as I know from turbocharged engines, an advantage could be that an engine with pre-chamber can operate in lean condition with reduced power loss. However, for a naturally aspirated MotoGP engine it will be a challenging development task.
“Nowadays, if you operate the engine in the normal way you’ll see quite a significant power loss between lambda 0.9 and 1.0. That drop could be reduced when you go to faster combustion, and here prechamber could help you, perhaps.”
What are your views on counter-rotating crankshafts? “That’s mainstream these days. At one point, during our development, we followed the mainstream. There are some gyroscopic effects to consider, especially in the wheelie phase, but how significant they are or not, I think is difficult to answer.” Is steel piston technology used in MotoGP? “I don’t know. Certainly that could be interesting in the future, in combination with leaner engine operation.”
Are there any areas of materials or coatings development you’re currently pursuing? “Friction reduction is an ongoing development. As everybody who’s dealing with IC engines knows, the highest amount of friction is in piston-toliner contact, followed by the bearings. So we tend to work on these as a priority.”
On track
We asked Trieb: you’ve introduced a ground-effect diffuser fairing this season, how has that extra downforce affected the ongoing development of your engine? “The additional downforce reduces wheelies and improves the stability in the raking phase, so the bike in general is stable. That means we are more at the engine limit, meaning we can apply the full engine power to the track more.”
Has the engine cooling requirement changed this year? “We have a slightly smaller [engine cooling] radiator to help aerodynamics. This year we are running slightly hotter, but the engine can deal with that.” How significant is fuel consumption? “The efficiency of our engine is not so bad. We have three or four tracks where we need to prepare leaner maps to finish the race.”
Are there any scenarios where you run on fewer than four cylinders, to help with fuel consumption? “In the engine brake phase we operate just one cylinder. I think that’s quite a common strategy.” How easy is the bike to dial-in relative to last year? “In general, I think compared to last year, we have made a step. And if it’s easier to make a lap time it eases your race weekend. It’s a massive difference whether you start from sixth position or 14th. And that I think is the key factor for a successful race weekend.”