‘We build our MotoGP engine so the electronics have to do as little work as possible’

MotoGP

Kurt Trieb designed the engine of KTM’s RC16, which has won as many races as Ducati’s Desmosedici over the past season and a half. Trieb tells us about his design philosophies and reveals that the RC16 isn’t a 90-degree V4

Kurt Trieb with the KTM RC16

Kurt Trieb and KTM’s RC16, winner of five of the last 23 MotoGP races

KTM

KTM entered MotoGP four years ago and is already battling with rival manufacturers who have been racing in the premier class for decades. Only Yamaha has won more races since the start of 2020, with KTM’s five victories equalling Ducati’s win rate and bettering that of Aprilia, Honda and Suzuki.

At the heart of KTM’s RC16 is its engine, the same 1000cc 90-degree V4 configuration used in Ducati’s Desmosedici, Honda’s RC213V and Aprilia’s RS-GP. At least, that’s what we always thought. Except that our recent chat with KTM’s Head of Engine Development Road Racing Kurt Trieb revealed that the RC16 isn’t a 90-degree V4, after all.

There’s no doubt that Trieb – who also designed KTM’s Moto3 250cc single and its original 2005 MotoGP V4 (used briefly by Team Roberts) – has played a huge part in the RC16’s success, from his original concept to detail work on firing configurations, combustion and so on.

Nowadays electronics take up more time than any other aspect of machine performance in MotoGP garages, but Trieb quickly realised the importance of creating an engine that doesn’t require too much interference from the various electronic rider controls, which all slow the bike down, rather than speed it up.

 

You used to engineer Formula 1 car engines, which are all about maximum horsepower, whereas MotoGP bikes are mostly about part-throttle, does that make the job more interesting – chasing a friendly engine instead of big numbers?

My background is automotive and automotive motor sport – engine design in Formula 1 and touring cars. The biggest difference in motorcycles is that you have the clutch and gearbox to think about. In car racing you don’t worry about that stuff, so that’s a big difference in MotoGP.

And, yes, in MotoGP the engines are used from 8000rpm to 18,500rpm. That’s a big difference from an F1 engine, where in my time there, the engine was always working above 12,000rpm. That’s something you cannot do in motorcycles.

What’s your speciality – engine architecture, combustion design or what?

It’s everything. From the start of the RC16 project it was very important to have a reliable and simple base which works, so you can go testing and develop your own package.

KTM engine

A 2020 RC16 engine in KTM’s new Motohall exhibition centre in Mattighofen, Austria

What’s most important when you’re trying to make an engine work effectively on part throttle?

Internally, it’s basically the gas exchange [the cycle of supplying fresh air and removing exhaust gases] which you have to set up correctly. That’s port design, turbulence inside the cylinder and so on.

Everything has to work together. If you have a port that gives good flow figures that doesn’t necessarily mean you’ll have better combustion. Let’s say the combustion could be bad at low throttle or at low engine speed, even if the port flows well, so it’s all a bit of a compromise and a combination.

What’s the difference between an F1 cylinder and a MotoGP cylinder?

Formula 1 has much shorter-stroke engines, whereas in MotoGP we are limited by the 81mm bore restriction, so I think we are racing long-stroke engines!

Can short-stroke engines be too revvy, too peaky for bikes?

I must say I’ve always been a fan of short-stroke engines. I think you can make them work well, especially if you get the port design and valve lift correct, because this can compensate for some of the benefits you get from longer stroke engines.

In MotoGP the acceleration limit until you reach fifth and sixth gears is grip and wheelie, not horsepower. How does that affect your work, or do you leave that to your electronics and downforce people?

Let’s say that in the first four gears of a MotoGP bike normally you cut the power with the electronics. From 2019 to 2020 we made a good step with our engine, by adjusting the power delivery to what the rider can naturally use on track, so that the electronics have to do as little work as possible.

So you designed an engine that doesn’t need electronics so much?

We still need electronics, that is clear, but let’s say we’re now working more in that direction.

Since Michelin returned to MotoGP the back tyre has become a crucial part of stopping the bike, so negative torque is very important. So when you design an engine do you think about getting the bike into corners as well as out of them?

You need negative torque to stop the bike, that’s clear. What we’ve learned is that you need an engine that burns consistently at very low throttle openings. If you close the throttle completely the engine will shut off and there’s a fine line where you can still keep the engine burning and also deliver some negative torque for engine braking. For the rider it’s very important to have a consistent feeling in this area of corner entry – because if the engine shuts off and cuts in again it’s a disaster.

Brad Binder on his way to winning the 2021 Austrian Grand Prix

Brad Binder chasing the lead pack on his way to victory in the Austrian GP, chased by fellow RC16 riders Iker Lecuona and Miguel Oliveira

KTM

Some factories use an adjustable exhaust valve in the exhaust to modulate negative torque. What about you?

We have tested these but they never rated as a must-have. As I said, if you have an engine that doesn’t burn at very low throttle openings then you have a problem. If this is the case an exhaust valve allows you to create back torque with the throttle, so it’s a workaround.

So if you do your work right inside the engine you don’t need one?

Yes.

How many different firing configurations have you used since the beginning of the RC16 project while trying to find the best irregular firing from the engine?

We are now on our third version of the firing order. First we had the screamer, then the big bang and now we have the long bang, or whatever you want to call it. In the end it’s an irregular firing order across the cylinder bank, so you don’t have constant pulses going to the rear tyre, you have inconsistent pulses.

What does this offer? People have talked about this for years…

I don’t think there’s any fixed explanation, so I can only tell you what I think. I think it’s related to the frequencies and the gas exchange, with the irregular firing configuration translating well to the rear tyre.

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If you have a screamer engine with two cylinders firing together then everything happens at higher frequencies. I compare a screamer to a two-stroke – when you keep the throttle constant and the exhaust starts working then the engine revs go up without you changing the throttle position. This is exactly what you don’t want and this is what happens with a screamer.

That’s my understanding, so at very low throttle openings or at very low differences you have quite a reaction from the engine and this is what the rider cannot handle. I think that’s the biggest difference.

When Yamaha introduced its first big-bang MotoGP engine in 2004 its engineers had some unusual theories about why big-bang engines work. What are your thoughts?

With the Yamaha and Suzuki [inline-four] engines it’s another story. It’s related to the irregularity of the crankshaft movement. For instance, when a cylinder is in the compression stroke you have deceleration and after ignition you start to accelerate again and this gives you variations in crankshaft speed. With the type of crankshafts that Yamaha and Suzuki use they get a better regularity of crankshaft rotation.

KTM 2020 RC16

KTM’s 2020 RC16 was the biggest step forward in engine and chassis performance

Oxley

Why did you choose to build a V4?

Very simple – power! – because you don’t have to compromise the inlet and exhaust ports. Another aspect for us was that with these high-revving engines the longer the crankshaft and the camshafts the more problems you get with torsional and bending vibration.

As I said before it was important for us to have a reliable mechanical base. This is achievable with an inline-four, no question, but it requires more development effort.

Was choosing a 90-degree vee angle the obvious way to go?

In fact we have slightly less, 86 degrees. That was decided at the beginning of the project, due to packaging considerations. We didn’t want to have a balance shaft, and 86 degrees is the limit for getting away without a balance shaft.

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Honda has a 90-degree vee and if I was making our engine today I’d probably make a 90-degree vee, but it’s not a big deal, it doesn’t make a big difference.

Does the RC16 use an outside flywheel, like Ducati’s Desmosedici, so you can adjust crankshaft inertia?

We only have a small alternator at one end of the crankshaft. In our engine we get crankshaft inertia from the crank webs.

Isn’t useful to be able to adjust crankshaft inertia, according to the rider’s request?

We’ve had many big discussions about what’s the correct inertia but we’ve been something in the same range for the last two or three years. And from what I’ve seen from our competitors they’re not much different. We’re all in the same range, let’s say.

What’s the difference between your Moto3 and MotoGP cylinders?

The valve size and valve angle aren’t so different. The main thing is the ports, valve lift and cam profile, because Moto3 engine rpm is limited in the rules, so the engines run at lower speeds [13,500rpm maximum].

The four-stroke engine has been developed for more than 130 years, what will be the next steps? Surely any gains now must be tiny?

Yes, but surprisingly there are gains. It’s always an ongoing development and even if you’re only making small steps they can be significant.

KTM celebrations at the Red Bull Ring 2021

Celebrating Brad Binder’s second MotoGP win, last time out at Red Bull Ring

KTM

There’s talk of MotoGP moving to so-called carbon-neutral fuels in the not-too-distant future, what are your thoughts?

From what I’ve heard we are talking about two different things.

The first is bio-fuel with 20% ethanol, which doesn’t make a big difference from an engine point of view, so that would be relatively easy to do.

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The second is synthetic fuel, in which you use hydrogen and mix it with carbon dioxide, and this is another story. I don’t have any experience with this kind of fuel but from what I hear the knock limit [a critical point in the combustion process] and octane numbers are much lower, so you have to accept lower performance from the engine. Or you can add some additives to fix this problem.

I think this is what F1 is doing now, so there’s development ongoing and they’ve committed to use this fuel from 2025, so I think MotoGP will follow this way. Developing a new combustion process is a big development task, a big challenge. In the motorcycle industry we don’t have the same resources to do this that they have in the auto industry.

But to be honest, motor sport will never be good for the environment – that’s how it is.

If synthetic fuels reduce performance this would surely be a good thing for MotoGP, with the bikes now reaching 225mph/360kph?

Yes, I agree that the speeds we are seeing are getting too high.

Next year all MotoGP factories will be allowed to have new-spec engines for the first time since the start of 2020, so presumably the bikes will be even faster?

Yes, I expect all out competitors to make more steps. Our own priority is more power! Ducati still sets the benchmark in this area and you can see weekend after weekend where their advantage is – if you can overtake on the straight it can change your race completely.

If you have good acceleration and top speed then it’s time for free, because the rider doesn’t have to take risks to gain that time. We want to draft and get alongside the Ducati – we are all in the same boat!

KTM seems able to overcome problems quicker than any other factory in MotoGP, why is this?

I think our big advantage is that decisions are taken very quickly. If I or someone else has a problem we go to Pit [Beirer, KTM’s motorsport director], ask for some money to fix it and we get the money. In other companies, as far as I know them, there are decision processes that take longer, which slows everything down, which makes a big difference.

This doesn’t mean that we have an unlimited budget – that’s clearly not the case – but if there’s an emergency and we can show that we have a solution then normally we can react quite quickly. That’s the difference between us and other companies.