Is the in-line four cylinder motor about to become the most developed engine for performance motorcycles? BMW’s choice for this platform and Yamaha’s development of their cross-plane crankshaft engine are two obvious points. What if either of those manufacturers combine their strategies with something similar to the Horex’s staggered piston arrangement? The Horex 6 cylinder engine head cover is under 17 inches across. Would a similar reduction be achieved with a staggered four, resulting in an engine more narrow than a triple?
How about mass centralization? Bott Power’s Moto2 bike has tremendous mass centralization (see photo). Its gas tank is primarily underneath the rider’s mass when the rider holds the clip-ons. This is arguably more centralized than Buell’s approach. The torque advantage of the cross-plane crankshaft, the staggered piston arrangement of the Horex, and the mass centralization potential of an in-line configuration could be difficult to beat on the street and on the track.
The twin cylinder engine could be developed to the point where manufacturers begin to dwindle the amount of chassis used by strengthening the heads as structural connection points, but at this time, that seems to be very costly (e.g. Ducati’s patent for a “frameless” motorcyle using carbon fiber sub frames attached to the engine). What other areas can the development of the sporting twin be taken?
Link: Bott Power
Related: Horex
Merlin says
I think I somehow missed the transition from staggered inline 4s (narrow v-4s) to ultralight twins. Are you implying that a narrow v-4 could, like a twin, also be made “frameless?” I’m not sure I get your point.
Carlo says
Englis version of the BOTT site: http://bottpower.com/eng/
[google translate is awful!]
I’m no mech engineer, but what about the structural strenght of a frameless bike?
Is it comparable to that of, say, a tubular frame like the normal Ducati’s?
Will13 says
Interesting piece. Having worked in the road race realm, both with cars and motorcycles, topics like this are of great interest to me.
In terms of engine packages for racing, the four cylinder engine is very attractive until you begin to play with aerodynamics. It was the aerodynamics on the 2009 BMW S1000RR WSB that presented the most problems on the track, and several BMW team members including Troy Corser have commented on the challenges of wrapping the inline four in a tidy aero package to be able to compete against Aprilia and Ducati whose engines are half as wide, thus allowing for a better aerodynamic package. The smallest hole in the air will always offer the greatest advantage, which is why V twin and V4 engine layouts are currently seen as having the advantage.
I’m not familiar with the Horex mill, but it sounds much like the VR6 layout made famous by VW. I can honestly see this layout gaining popularity as a way to retain a high cylinder count but offer the aerodynamic advantages of an engine with a smaller cross section that would normally have a smaller cylinder count.
Carlo says
yep, it is indeed the same as the VW VR6:
http://thekneeslider.com/archives/2010/06/15/horex-motorcycles-returns-with-new-1200cc-vr6/
Simon says
Lancia has had a “VR” 4 in the ’70s. 1300cc 90 hp. A dutch guy has built a motorcycle frame around it in ’75, he called it a Lancia KS 49 P1.
pdub says
Good questions for thought. The I4 obviously has some very good virtues as does the Vtwin. Are either the pinnacle of evolution? No one will rest on that notion and it will be very interesting as both designs converge towards the advantages of the other. A frameless, staggered 4 with a crossplane crank? Interesting. It does make me though think of designs that have been discarded like the square 4 configuration? That could be compact and narrow but why was it left behind?
JR says
The Motoczys bike that was in development before the D-One-g-One-Tal was a VR4 right?
Simon says
Motocsys had an inline four cut in two with two counterrotating cranks, and mounted lengthwise in the frame.
Doug Staab says
Hello Merlin – The transition to v-twin construction was to compare the two types of engines in light of the first question: “Is the in-line four cylinder motor about to become the most developed engine for performance motorcycles?”
At this time, the inline four configuration appears to have a variety of large topics to explore than twins (over and above the incremental advancements that all engines continuously undergo). I could think of only one large topic related to a twin configuration that recently surfaced & that is Ducati’s frameless patent. I suppose any engine could be made strong enough that everything bolts to it, especially if composite material is used, but we must factor in mass production. The metal mass of a rear cylinder in a twin config. seems easier to go frameless than an inline motor (at least towards the rear of the bike). That’s why I mentioned the twin.
Towards the front of the bike, inline motors (and possibly Aprilia’s v4, and twins like Buell and KTM) have motor mass that allows front suspension systems to be mounted. It is doubtful the market will accept an alternative to the tele any time soon, but as electronics are increasingly necessary to control power, the next focus for improving performance would be to cut weight. So, maybe funky front-ends will get more attention. James Parker’s design has cut an impressive 22 lbs. from a stock GSXR because he is able to mount his design to the motor, cutting out large amounts of chassis mass. (By comparison, it will be interesting to watch Ducati’s presumed aluminum frame-and-airbox-in-one design get developed.) Martin Wimmer’s design also plays into an inline motor, (and possibly Aprilia’s v4 or twins like Buell or KTM) because it uses a swinging arm located just above the front wheel that can be mounted to front of the motor.
Doug Staab says
Although direct injection is applicable to all engine configurations, it is worth mentioning as possibly another large development topic for inline motors. Motus Motorcycles states two advantages of direct injection are compact head design and increased torque. In reference to Will13’s comments, the I4 motor would benefit more from compact heads (to go along with a staggered piston arrangement) & increased torque than would the twin configuration.
inline-staggered-piston-crossplane-crank-direct-injected-4
todd says
sure, the inline-4 gets the most development because it’s the most popular on the street. However, I feel the V-4 is even better (as implied by others here). It has all the power benefits of an inline-4 but without the detriment of the long, flexing crankshaft. A V-4 can have a lighter crank, is more balanced, can rev higher, and is narrower. There are challenges with exhaust length and routing on the rear cylinders as well as the additional manufacturing cost of more components.
One can argue that, on the street, this all doesn’t matter much. However, a V-4 has got to be the best sounding engine -by far- followed by an inline-triple, a 90 degree twin, and a crisply tuned 45 degree twin (without fat, burbly pipes).
-todd
Spouler says
I saw Honda’s RC211V V5 in action at the Shanghai MotoGP in 2007 (or 2008? Can’t remember). The Shanghai circuit was criticised as having too long a straightaway since it was also designed to host F1, but it was the perfect opportunity to witness how Honda’s V5 blew away the competition in torque and speed. To this day I believe that they were on to something if they could just work out the bugs.
Doug Staab says
“One can argue that, on the street, this all doesn’t matter much”….but it does matter on the street, too. I’m not the only die-hard twin cylinder fan that would be willing to own a slimmer, torquier inline 4
Doug says
“sure, the inline-4 gets the most development because it’s the most popular on the street.” – More to the point are the number of untapped, broader development topics that the i4 platform has currently available compared to untapped, broad topics going on right now with twins, regardless of popularity.
In-line 4s have been very popular for decades, but only recently has the cross-plane crank made it to production on an i4. Likewise, only recently have the Horex staggered piston & Motus direct injection designs been considered for motorcycles.
Will13 says
@ Doug Staab
Hi Doug, nice thought-provoking article! Above you mention “inline-staggered-piston-crossplane-crank-direct-injected-4”. That maybe a bit much to request even from modern metalurgy in terms of crankshaft design, but I’m no engineer. I think that Yamaha’s “Big Bang” crank was a solid step forward in getting more torque out of the inline four.
Moving an I4 layout to a staggered arrangement would, in my opinion, be much more difficult to balance at the crank, and therefore would probably be better to use a VR or square four layout with the option of two cranks counter-rotating to provide a neutral balance. Again, I’m no engineer, so this is just off the cuff so to speak.
In terms of developed v-twins, I think the Britten was one of the best v-twins ever to grace the earth. As far as taking the v-twin engine configuration and using it to hang all the necessary bits off of for bike construction, I don’t see why it couldn’t happen as the Lotus 49 pretty much did the same with the Cosworth DFV in 1968.
Doug says
hey Will – by staggered piston, I meant the VR configuration (as opposed to a straight line), but I now realize some refer to the W engines as 2 ‘staggered’ banks of cylinders.
Simon says
Interesting discussion, remembered me of the Kawa KR250/350 tandem twin.
“The Kawasaki KR250 was a racing motorcycle built by Kawasaki from 1975 to 1982 for the 250ccm class of Grand Prix motorcycle racing. It was powered by a two stroke, twin cylinder engine. The motorcycle proved very successful winning many races and 3 World championships, in 1978 and 1979 with Kork Ballington and in 1981 with Anton Mang.” (source: wikipedia.org)
Just some thoughts to translate this lay-out to a modern (4-stroke) tandem twin:
– keep the small displacement and thus the small dimensions
– add MultiAir technology to optimise airflow (oops, cilinderhead size….)
– add a variable turbo to get some torque out of the small displacement
– add a dry sump to lower the centre mass
– directly bolt on a traditional rear-swingarm to reinforced engine castings
– directly bolt on a radd-like front swingarm to reinforced engine castings (www.pashnit.com/forum/attachment.php?attachmentid=1575&stc=1&d=1106490583)
– even weirder: combine all of the above and keep the 2 stroke cycle (in marine diesel style)
But hey: I’m no engineer. It’s just fantasy!
rohorn says
Simon,
If you are feeling ambitious, check out the old Rotax 256 – or BRC250 superkart engine…
Nick5628 says
Inline fours are the dominant force on the street. As for using the engine as a stressed member of the frame, John Britten proved that concept works excellently 20 years ago.
rohorn says
Tony Foale has a number of stressed engine conversion project pictures on his website – both are a lot older than the V1000. One uses a Z1 engine – and another one uses a CBX engine.
Sick Cylinder says
One problem with VR engine configurations in high power applications is design of the inlet tracts – this is normally overcome with forced induction – for this reason I don’t see it as a serious option for race bikes.
Kevin says
What about a 3 cylinder? Already narrower then a 4, more torque then a 4 but more rev than a V2, and no intake/exhaust routing problems.
Then how about a DI 2-stroke triple. Less height, ~50lbs less weight, ~35% more power and ~70% more torque. All while reducing manufacturing costs.
Doug says
Kevin – glad you mentioned the triple. It would be interesting to see another performance triple on the market, especially with the Japanese triple history. I don’t know if any manufacturer would be willing to enter WSB with a triple. Aprilia tried it in GP and couldn’t sort it out economically.
The thought of a VR triple is enticing. A triple that is close to the width of a parallel twin but includes the triple’s torque characteristics, revs, and character.
Sick Cylinder – wouldn’t the staggered config of a VR engine offer more space for the inlet tracks than a traditional inline config (while still reducing width)?
Will13 says
Having owned Triumph triples for the last decade, I have grown quite partial to the engines for their tsunami-like wave of endless torque and 10,000 rpm rev capacity.
When the Daytona 675 made its debut, it seemed to cause a rather large amount of panic throughout the industry. I was working at a Triumph dealer at the time, and the little Daytona just never ceased to impress me. I wasn’t the only one, as I remember hearing in 2008 that Benelli, MV Augusta, and BMW were all working on building a small triple cylinder engine to go head to head with Triumph’s 675 powerplant. Over time I think more manufacturers will adopt this engine configuration for its sporting performance and small packaging.
In terms of the Japanese, I think they’ll continue to develop the I4 mainly due to the current global economic conditions. Yamaha’s new FZ8 offers some proof of that.
I’m surprised the rotary hasn’t been mentioned yet, with Norton making a return with the NRV models and all. There’s a terrifying twin indeed.
deckard says
Engine width is not as big a factor in aerodynamics as it may appear initially. The size of the radiator is the biggest problem, and all WSBK bikes tend to run a radiator with the same general capacity. An narrower engine behind the radiator may allow for more efficient airflow through the radiator, but this is a secondary effect of engine width on aerodynamics, not a primary effect.
todd says
engine torque is not determined by cylinder arrangement or quantity rather it is a product of displacement. Other factors affecting torque are valve overlap, lift, and duration, inlet and exhaust tract diameter and length (high velocity air is good), inlet charge temperature (density), fuel atomization, compression ratio and combustion chamber shape (good flame propagation)…
Large-bore engines with reduced cylinder count are typically “tuned for torque” since higher RPMs (“free” HP) are not as achievable. A four cylinder (of any arrangement) can actually be tuned to provide more torque than a single or twin (of equal displacement) since it can afford a larger number of smaller throttles and valves without sacrificing as much power (HP / RPM).
The only reason people tend to think V motors, in particular twins, have more torque is because they are typically at least 1600cc and inline-fours are around 600cc. When racing, and adhering to class restrictions, the difference is not so apparent. The choice of cylinder quantity and configuration is usually left up to the marketing department to approve. In the case of BMW, marketing finally felt it was OK to develop a (proper) inline-4. In Ducati’s case, marketing felt it was acceptable to have a V-4 since it looks like a twin from the side. All envy Honda because they are free to develop any cylinder configuration that makes the most sense for the type of power and packaging they require in a race effort.
-todd
Tinman says
Does any company develope a engine, or just copy the features currently in vogue? Most sane riders agree that power is not the issue anymore, the control of the power is where the advances are being made. The European builders are currently ahead in the electronics front, but the battle has just begun. You can be sure that the Asians are very busy doing more reverse engineering at an furious rate.
Mule says
Tinman, another concern that the factories have to deal with is so much power, they can’t keep tires on the bike. Like at Daytona on TZ750’s in the 70’s-80’s and now at Daytona the Superbikes with well in excess of 200HP, tires get dangerous quickly.
So now we have a 600cc Daytona 200. Getting power is not the issue. It’s more toning down through electronic management, the harsh delivery of said power.
Hugo says
The late Antonio Cobas was apparantly working on a MotoGP bike with a Triple:
http://2.bp.blogspot.com/_0bp8mkNN2Lw/SFK4ZMHFuAI/AAAAAAAAABM/Wkgl604vUtI/s1600-h/usuarios-1.lycos.es.jpeg
and a composite frame/airbox like the Ducati MotoGp bike now has.
I even thought Honda was playing with the idea of a 800cc V-triple based on the V-five MotoGP engine…would be interesting to see a V-triple with a similar configuration like the VFR1200 now has (one cilinder at the back, small in width and two cilinders at the front, to get more weight on the front)
And like Deckard says the radiator is the problem, both regarding location and size.
I think the main reason why the 4-in-line is the most popular engine is costs (A 4-in-line is much cheaper to produce then V-engines (less castings, camshafts, etc.) and it is relatively easy to get power from them.
Doug says
I agree about the radiators, but the width of an engine can also impact handling due to chassis (weight) considerations. And, who wouldn’t want a slimmer bike while maintaining the same cylinders/power?
todd – torque was mentioned in light of the cross-plane crank providing more torque lower in the revs while not sacrificing high rev power. It is widely written that this new engine is much better than other i4 lower in the rev range.
todd says
Doug, don’t be confused; the layout of the crankshaft cannot add overall torque to the engine. What it does is allow fewer cylinders to be at TDC and BDC at the same time. This occurs regularly in a conventional flat-crank and with all the pistons coming to a stop at the same time then immediately speeding back up again causes secondary torque pulsations (+ torque, – torque) or better, vibration. These pulsations work their way back to the wheel and create the tendency for the tire to lose grip and then gain it, lose it and gain it again. This pulsation occurs at twice the frequency of the engine RPM yet it is enough at race limits to cause vagueness out of corners at best and loss of traction at worst. Staggering the crank throws also allows a greater staggering of the power pulses (similar to the old Big Bang theory) so there will be a longer pulse of tire gripping smooth-calm before the next set of power pulses gets it all squirrelly again.
-todd
Doug says
todd – thanks for the explanation, no confusion here. I have read similar descriptions and the end result is better power being transferred to the wheel, lower in the rev range. In extreme situations, such as Ben Spies championship season on the R1, he mentioned being able to get on the throttle sooner out of a corner.
pdub’s comment sums it up: “…No one will rest on that notion and it will be very interesting as both designs converge towards the advantages of the other.”
I put the brief post together largely because i found myself thinking about the what-ifs of the i4 motor….which baffled me after thinking for decades I’d never go back to an i4 after a twin
Rowey says
Ducati build L-twin’s not V-twins right? So why not an L-4 (90 degrees)? A perfectly primarily balanced 4 cylinder, no flexing crank as someone else mentioned, great top end and low down torque, narrow package, would still offer a roaring engine tone and great cooling as all cylinders would receive air and not be blocked by others. Apart form packaging, what is the reason for Aprilia using a 65degree angle?
Has anyone seen the inside of the new Ducati 1199 engine? Massive piston heads with very, very short con-rods. The piston heads seem almost flat. Worth a look lads.
Rowey from London.
*Looking for a job after passing this year of Motorcycle Engineering Design[BEng] at Kingston University*