KTM’s head of off-road engine growth, Florian Bretterebner, gives an interesting perception into the important thing engine updates launched to KTM’s landmark 2024 enduro fashions – each two-strokes and four-strokes.
Within the wake of this 12 months’s worldwide media launches for the 2024 enduro fashions from KTM and Husqvarna, there was numerous speak concerning the truth these bikes got here with 95% new components – together with a radically totally different ‘stiff body idea’ and WP’s all-new XACT closed-cartridge forok. And that’s completely comprehensible as a result of the new-generation chassis and suspension guarantee these 2024 fashions are arguably each manufacturers’ most radically up to date enduro machines ever.
However amid all that rolling chassis fanfare, a number of the very important updates to each the two- and four-stroke engines received ignored. So, to assist shine a highlight on the 2024 vary’s key engine mods, we sat down for an enlightening chat with Florian Bretterebner – the likeable dude who heads up the design workforce behind KTM’s off-road mannequin powerpack growth…
TM: Florian, can we begin together with your official job title … as a result of it’s an convoluted one, proper?
SW: Sure [laughs]. Formally, I’m Head of Powerpack Off-Highway ICE – which stands for Inner Combustion Engines – in KTM’s R&D Division in Mattighofen.
And also you’ve been at KTM for a couple of decade now, working with engine growth royalty akin to Michael Viertlmayr.
I’ve really been with KTM for 11 years now. And, sure, Michael Viertlmayr is my boss. He’s now Vice President for all KTM engines – Avenue and Off-Highway – and I took over his function as Head of Off-Highway.
Give us an concept of how your off-road engine workforce is structured.
Nicely, my workforce is shared throughout motocross and off-road fashions, and it’s break up into six groups: Mini, 50-85cc two-stroke, 125-150cc two-stroke, 250-300cc two-stroke, 250-350cc four-stroke and 450-500cc four-stroke. Everyone on these groups is completely into using. They’re all very centered they usually put a lot effort in to creating their engines. Plus, every workforce has devoted take a look at riders. And so, it has been actually gratifying for us to listen to all of the optimistic suggestions from unbiased journalists after this 12 months’s worldwide media launch for the 2024 fashions.
Understandably, the all-new XACT CC fork and body stole the limelight with KTM’s 2024 enduro fashions. But it surely feels to me that the importance of some of the of the bikes’ engine mods had been a little bit ignored?
I agree as a result of there have been so many mods throughout each two-stroke and four-strokes engines for 2024. And I don’t simply imply the transfer from the TPI (Switch Port Injection) to TBI (Throttle Physique Injection) fuel-injection system for the two-strokes. The work it took to replace the four-strokes’ engine instances alone is very large and required an enormous quantity of design effort and engineering talent. Then there’s all of the updates which might be hidden from view – akin to how the transmission is lubricated and the way the clutch is lubricated. For instance, on the 450cc engine, the lubrication of the clutch was by way of sucking the oil out of the crankcases, whereas it’s now a pressurised system – like we already use on the 250 and 350 four-stroke engines – which is far more environment friendly. That is only one instance of numerous small however very important particulars we’ve improved for 2024.
Coming again to the engine mounts; that’s a drastic change as a result of the engine instances’ mounting factors for all 4 four-stroke engines wanted to be relocated so all of them lined up with the similar body now used throughout the 2024 250, 350, 450, 500EXC-F fashions. Discuss concerning the chassis guys making the engine workforce’s life troublesome, eh?!
Nicely, sure [laughs]. It was an enormous and really complicated job. However we didn’t see that design requirement as troublesome as a result of we’re all on the identical workforce, and all of us realised the longer-term advantages of constructing this variation. Then it was merely a matter of discovering one of the best resolution – which was tougher for some capacities’ engine instances than others.
Talking of element ‘standardisation’, there are actually solely two totally different transmissions throughout your complete enduro vary – one for the 150EXC, and one for the opposite six fashions – albeit with totally different major and secondary gearing, proper?
That’s proper. Additionally, the shifting mechanism is now the identical from the 250EXC proper as much as the 500EXC-F. This standardisation was not about value financial savings, however to enhance efficiency. In contrast with the 350’s transmission, the space between the enter shaft and output shaft on the 450 and 500 had been bigger, however the gear-wheels themselves had been thinner – which was not the hardest or most compact design. That’s why we adopted the 350’s current transmission design to the opposite three four-stroke fashions for 2024, after which fine-tuned every of them with their very own major and secondary gearing.
Talking of gearing, I perceive the gear used for the oil pump has modified from plastics to a sintered materials for 2024.
Precisely. The oil pump gear was constructed from a barely lighter bolstered plastic, however the sintered metal gear now used is far more strong. This is only one of many examples of mods we made. There have been so many, they couldn’t all be captured by the replace details about these new bikes.
Okay, let’s speak concerning the introduction of the two-stroke Throttle Physique Injection (TBI), which – mixed with the brand new digital power-valve – is arguably essentially the most important engine mod to the 2024 vary. How did you guys handle to adapt the TBI system to those bikes and nonetheless adjust to Euro5 emission regs? As a result of, up until not too long ago, solely the TPI system would comply.
Nicely, we developed each the TPI and TBI techniques concurrently. In 2018, we launched the primary two-stroke enduro fashions with the TPI primarily as a result of that system was higher when it got here to emission ranges. However in fact, we continued to review and develop the TBI system with many simulations to raised perceive the way it labored. And thru that course of, we had been in a position to get the emission homologation for the TBI system.
However introducing TBI isn’t just about emissions; it’s additionally allowed efficiency beneficial properties, proper?
Completely. And that’s the reason we labored so laborious to get it homologated.
Clarify how the TBI’s twin injection works. I perceive there’s now an injector both aspect of the throttle physique’s butterfly.
That’s right. The injector on the engine aspect operates on a regular basis. Then the second injector begins to function at bigger throttle openings and better engine speeds once you want extra gas mass. You’ll be able to see that, when the butterfly flap is open, each injectors spray from the underside of the throttle physique to create a extra homogeneous air/gas combination. And when you’ve this extra constantly blended gas and air enter the combustion chamber, it makes it a lot simpler to search out efficiency beneficial properties – although it’s nonetheless crucial to have an environment friendly switch port design to make sure the TBI works optimally.
And that was the difficulty with the TPI system, proper? With a much less homogeneous air/gas combination, the TPI bikes’ RPMs would ‘hunt’ up and down once you held them at a continuing throttle setting.
Sure, that’s proper. And the extra homogeneous air/gas combination with the TBI system additionally offers you a extra instantaneous response to throttle inputs.
In layman’s phrases, why is the combination extra homogeneous – or constant – with the TBI system?
It’s complicated, however in easy phrases, it’s as a result of the air and gas are mixing ‘earlier’; they’re mixing within the throttle physique fairly than within the cylinder’s switch ports themselves. With the TPI system, the place the injectors had been spraying the gas in opposition to the route of the airflow, the blending was nonetheless fairly good. However with the TBI system, you’ve an extended distance for the blending course of to happen earlier than that combination is combusted. And at increased revs, a constant combination turns into essential.
Is it honest to say that this TBI system is just nearly as good as its companion in crime, the all-new digital power-value?
Sure, that’s honest to say. KTM shouldn’t be the primary to introduce an digital power-valve, however I consider our digital power-valve is a intelligent design and works very successfully. It entails a step-motion motor that prompts a shaft which runs from the left- to right-hand aspect to open and shut the auxiliary ports completely and with very small tolerances. As two-stokes are super-sensitive to thermo-dynamics and the timing of their port opening, this design was crucial to optimising efficiency. On the shaft, some metal-injected moulding components are mounted, which function cams. And people cams actuate the primary exhaust flap. Then there’s a secondary gear on the cam that prompts the auxiliary exhaust ports.
The ability-valve system on the earlier fashions additionally used a cam for exhaust ports, so how is that this one totally different?
Sure, the predecessor fashions did use a cam design with actually steep cam lobes. However this new digital power-valve design is far more bulletproof, plus it could possibly’t get caught.
Clarify what the brand new “KTC” (KTM Torque Chamber) is and what it does.
Nicely, it’s not new. It was really used on the 380EXC two-stroke a few years in the past however has been reintroduced for 2024 on the 250 and 300EXC fashions. And it’s one thing I’m very enthusiastic about as a result of I believe it performs a significant function within the engines’ efficiency beneficial properties. Successfully, it offers you want a two-header design as a result of with enduro bikes, you usually go along with an even bigger header and extra resonance quantity to generate extra torque down low – versus a extra peak power-oriented motocross bikes, which use a smaller pipe. With the KTC system on our 2024 enduro fashions, you successfully get each advantages. You don’t lose peak energy as a result of, as I defined, you shut it with the exhaust flap. However you continue to retain the facility at decrease revs, which is the place I believe the most important enchancment is achieved.
One more step nearer to a four-stroke type of energy, eh? Plus, the two-stokes now really feel so refined, they really vibrate lower than the four-strokes!
Completely. They now have a lot torque at low revs, they usually’re very responsive from low RPMs too. Which means a wider working window and higher rideability.
Talking about evaluating two- and four-strokes, how come the clutch-pull on the two-strokes feels noticeably lighter?
The stiffest diaphragm spring is used on the 500EXC-F clutch as a result of it has essentially the most torque and is the one mannequin to make use of the identical spring because the 450SX-F motocross bike. In the meantime the opposite capacities every include a lighter variation of that diaphragm spring. Additionally, the two-strokes have totally different friction plates of their clutches, which can contribute to that barely lighter really feel.
What occurred to the two-stroke fashions’ ribbed enlargement chamber design? When these pipes had been launched again in 2017, KTM had informed us they had been an unequivocal win-win; that they had been stronger than a traditional enlargement chambers and they managed to assist muffle noise emissions.
That continues to be true. However, with the change from the centrifugal to digital power-valve for the 2024 fashions, the extra area created allowed us to route the enlargement chambers in a extra compact means – that’s, nearer to the engine and body and with extra floor clearance – and nonetheless discover efficiency beneficial properties. Additionally, eradicating the ribs eradicated buyer complaints concerning the added prices related to eradicating dents from their pipe. Eradicating the ribs additionally helped us with homologation for the 2024 fashions, however that’s to not say the ribs received’t discover their means again onto our two-strokes at a while sooner or later, if you recognize what I’m saying [laughs].
I couldn’t assist however discover that you simply rode a number of of the 2024 bikes on the worldwide media launch your self. So, what’s your favorite and why?
On the four-strokes, it’s a toss-up for me between the 350 and 450. If I rode primarily enduro, I might select the 350 as a result of it does every little thing so properly in a wide range of totally different terrain. But when I rode a mixture of enduro and motocross, I’d go for the 450. On the two-stroke aspect, my favorite is the 300 – particularly in slippery circumstances. However I have to say that I felt actually snug on the 150 as properly. As soon as I tailored my using type, I simply cherished how light-weight and nimble it felt. It was nearly like a mountain bike to throw round, however it additionally places out an unimaginable quantity of useable energy for a small-capacity machine.
As with KTM’s 2023 MX fashions, there was lot of speak about serviceability for the 2024 enduro fashions. What stands out for you as examples of this improved serviceability?
I believe the brand new markings within the engine instances are very useful. There’s a casting mark for oil degree, and the identical goes for coolant. It sounds so easy, however once you do upkeep in your bike, it saves you from having to search for the house owners handbook to determine the place fluid degree must be. Equally, there’s a triangle mark on the instances to remind house owners which bolts require copper washers, plus really helpful torque settings indicated for a lot of bolts – or an important ones anyway. All quite simple, however all very handy for house owners. Then there are issues like, on the 450, we launched a plug within the ignition cowl so you may simply spin the engine to TDC and insert the crank bolt to maintain it there.
Thanks on your time, Florian. And congratulations to you and your workforce on the smorgasbord of recent and improved powerplants for 2024.
You’re welcome, Andy. It’s been nice to have you ever media guys take a look at the bikes on the launch and provides us your suggestions.
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