KTM is in a hurry. A hurry to become competitive in MotoGP with riders Pol Espargaró and Bradley Smith. Up to this point, KTM has only raced a four-cylinder engine with a “Screamer” firing order, i.e., combustion events equally spaced for each of the four cylinders. KTM is alone in using the Screamer engine. All of the other manufacturers have gone to a “Big Bang” firing order for MotoGP. This means, simply, that the combustion events are spaced unevenly, and even grouped, among the cylinders, in order to create more space between combustion events. Most teams believe this improves traction during acceleration and even tire life. Honda is the most recent convert.
Apparently, KTM has only tested its new Big Bang engine once, and that would be at this week’s private test at Le Mans. It would be quite ambitious to put the engine in a race this soon, but according to rider quotes (both Espargaró and Smith, as well as team test rider Mika Callio tested the Big Bang engine at Le Mans) that is precisely what KTM is considering. It will be no secret if they do, because the engine will sound distinctly different from a Screamer. We shall soon see.
Big Bang alright – Banged right off the track in the Race !
Just clowning around… But, it would be nice if this website would provide some coverage for the dirt bike crowd similar to what they do for the road goers. After all, it is called ‘Motorcycle Daily’. Myself, I really enjoy the new models, prototypes, customs articles they do here. Things that I would otherwise never see or hear about. Maybe do the same for dirt bikes. There is a lot going on in China, India, and Europe we never hear about.
The term big bang is perhaps used too often..but more space between firing pulses is a correct way to explain it…..with 90 deg V fours the crank throws can be 180deg from each other..that mimics a inline four..aka screamer Or conversely the throws can be aligned as one.. so all pistons rise and fall at the same time…aka 360 deg or droner basically like two Vtwins A cross plane inline four still fires evenly but phases the throws so that the companion piston is halfway up the bore instead of bottom or top …this cancels out the extra torque effect know as inertial torque…the object of the game here is not more power…but allowing for the tires contact patch to recover from each power pulse and make the bike more forgiving under power
With V fours it gets more complicated when using the narrow angles like the Aprilia etc…with regards to firing orders…but generally are droners
The current RCV and the Ducati are 90 deg fours…and to get them compact..are amazing marvels of engineering…for eg the exhaust valves are shorter..and the cam covers are angled….so the engine can be rotated to the correct orientation in the chassis
And it’s working for them. They are just a second off of the Li’l Danny’s pole time. They’ll post some top ten finishes before the end of the season.
Norm or anyone with knowledge of firing order options,
Is virtually any firing order possible by simply changing the point where the conrod joins the crank? Has any designer experimented with firing orders related to the Golden Ratio? If yes, what were the results?
The closer is an engine’s firing order related to the GR, the less symmetrical is the firing order, which I presume minimizes engine resonance and maximizes smoothness/reliability. The purpose of the so-called BB appears to be to decrease firing order symmetry, to maximize traction.
Think of a GR based firing order as a natural on/off switch on the force acting to break tire traction, with maximum non-symmetry in its timing sequence.
Thinking about this further: I presume, same as above, the more a traction control maintains a GR-based firing order, the better is tire traction and the smoother the engine runs.
Where’s Sheldon when you need him?
My understanding of BB’s effect on traction is that the contact patch of the tire actually has time to recover / refresh between power pulses. I’m not sure the Yamaha is a BB in terms of crankshaft orientation, I believe it to be pins clocked @ 90*. If that’s the case, then the firing order opportunity would to be fire all 4 cylinders in one crank rotation and scavenge all 4 on the next. Having heard the bike run at lower revs, it sounds like it isn’t, but that’s just my impression, not based on any real knowledge.
The benefit of v or x-plane in terms of mechanics is inertial smoothness. Whenever there is a piston at TDC or BDC (ie. Stopped), there is another traveling at Max velocity, offsetting the stopped piston’s momentum loss.
Prov,
The best explanation I’ve seen is over on superbikeplanet. Search “big bang.”
Here is an excerpt:
The main course was presented by Masao Furusawa under the title ‘What is Big Bang?’ Fursawa’s area of expertise is harmonics, so perhaps it was no surprise that he chose to use the analogy of signal-to-noise ratio to explain his theory. You understand that best from tuning your radio every day. Accurately setting your radio to the desired station means the signal comes in strongly and overpowers any background noise.
Noise is always present, what you want is a strong enough signal to render it irrelevant. So what is signal and what is noise in the context of a motorcycle engine? This is best explained by thinking about that word ‘connection’ you keep on hearing riders use in testing. This is shorthand for the connection between the throttle and the rear tire. In an ideal world, opening the throttle by 10% would deliver 10% of available power (actually torque, but never mind) to the rear tire. Life is rarely this convenient or simple, and racing engines certainly aren’t.
Modern electronics should be able to provide the linear throttle response riders crave; in Furusawa’s model a high signal-to-noise ratio. And what his research suggests is that that is what you do get—up to a critical rev level where the signal is severely distorted by ‘noise’. The question is, what is this interference? Furusawa says it is ‘inertia torque’, that is the torque due to the motion of the heavy moving parts in the engine—crankshaft, con rods and pistons. This is totally separate from the torque generated by the combustion process. At low revs, the level of interference from the rotating mass is insignificant, but around 12,000rpm it starts to become greater than combustion torque and by around 16,000 is double. This is counter-intuitive because you would assume, with a conventional 180-degree crank, that everything would balance out. Not so, as you discover when you look more deeply at the direction in which torque is exerted at different points of a crank’s rotation.
Combustion torque is easy to understand: it’s produced by ignition of the fuel/air mixture. Inertia torque is much trickier to define and understand. Let’s try. Forget combustion and just consider the piston and con rod travelling up the bore. At BDC the piston, con rod and crank pin are in line and no torque can be applied to the crankshaft (in fact at top and bottom dead centres, the con rod is momentarily stationary and vertical). Now move through 90 degrees. The big end of the con rod together with the piston is moving quickly with lots of energy and is about to decelerate to a halt at TDC. That energy of motion (kinetic energy) has to go somewhere, and the only place it can go is into the crankshaft. So inertia torque is positive in that it is applied in the direction of rotation of the crank. On the down stroke, the converse is true. The lower part of the con rod together with the piston has to be rapidly accelerated from rest at TDC to a high velocity, which requires an input of energy. That removes energy from the crankshaft so here inertia torque acts against the direction of rotation.
Without doing the math, you can see how this variation of torque over each revolution might produce some small variations in the torque seen by the tire contact patch. On your 180-crank, four-cylinder road bike, you won’t notice the effect because you don’t use high enough revs, but as this inertia torque is proportional to rpm squared, you can see how a 17,000rpm MotoGP engine might have problems. At those sort of engine speeds, the ‘noise’ of the inertia torque is ‘louder’ than the ‘signal’ of the combustion torque. The rider’s connection with what’s happening at the rear tire’s contact patch is lost both with the throttle open and with it closed.
End quote.
Furusawa’s explanation makes sense to me as a former geartrain designer for robots and industrial equipment. It’s about the torque ripple caused by the motor mechanicals overwhelming the combustion torque signal. Minimizing the inertial torque ripple of the engine leads to the good “feel and connectedness” that racers want.
Furusawa’s explanation addresses inertia, but not syncopated
ignition (big-bang firing). What he’s referring to is addressed by “V” or cross-plane engine configuration where piston’s can trade inertial energy to smooth output at the crank. Big bang firing is meant to create gaps in the points of highest stress at the tire’s contact patch. These are separate concerns.
It’s been awhile since I read the full article, but if I recall, because both concepts address traction at the rear wheel, they are not 100% separate concerns. In fact, the article seems to paint the concept of managing crank inertia as superseding the big bang idea.
That’s an interesting thought. I’m sure that they would have to brew up a new crankshaft. Even if it is a flat plane crankshaft they may need to install a new one so that two cylinders don’t fire at exactly the same time to prevent undue stress to the transmission. The transmission may have been designed to fire cylinders in pairs. but normally they are designed to handle one piston firing at a time. They can group them very close. But if they fire simultaneously, you are doubling the load on the transmission.
Or at least that was what the story was back in the big bang two stroke days.
go boys – time is a wasting. Kick it.
We need more motocross coverage instead of this sissy street bike crap.
I think that you have come to the wrong place buddy. Dirt bikes have slowly ceased to exist here. Almost like AMA road racing.
Don’t see no street bikes here. Move along.
Just clowning around… But, it would be nice if this website would provide some coverage for the dirt bike crowd similar to what they do for the road goers. After all, it is called ‘Motorcycle Daily’. Myself, I really enjoy the new models, prototypes, customs articles they do here. Things that I would otherwise never see or hear about. Maybe do the same for dirt bikes. There is a lot going on in China, India, and Europe we never hear about.
Right! ‘motorcycle daily’, not motocross daily. bookmark MXA and Racer-X, for a daily dose of mx. I don’t think this page is MX oriented, these are not the droids you are looking for.
http://www.dirtrider.com
why not let Roger D take a look at it?..
Gee, I don’t know, I kinda like screamers …
Who doesn’t desire a big bang?
There’s nothin’ like a big bang with screamer!
can’t we have both…?
Maybe its because of sketchy track conditions, however KTM is in the top 10 in FP2!
gorgeous ride…. go KTM
I was at the race in Austin and KTM had a noticeably different sound. I assumed it was a triple.
They sounded awesome but were at the back of the pack.
re: “They sounded awesome but were at the back of the pack.”
aw man.
Ready to Race?
oh look everybody there it is, the KTM variation on the “hammerhead” theme.
Is this the same as what the cross-plane crankshaft engine in the Yamaha’s have?
Same concept, firing intervals are likely different due to the different engine configurations (V vs Inline).
Big Bangs have been around in GPs since the 500cc 2-stroke days and long before that in AMA dirt track, when twins were retimed to fire on the same revolution (Twingles).
One has to ask, if all of the proven v-4 bikes used a particular firing order, why would KTM try something different?
Theory has (or had?) it, that traction control has become a better and more precise way of solving the problems Big Bang firing orders were previously employed to solve. Practice may have turned out differently…
re: “if all of the proven v-4 bikes used a particular firing order, why would KTM try something different?”
wait which F/O do you mean…? screamer or BB…? the proven V4 bike is the Honda which heretofore used a screamer with great success (albeit overtop B’stones) but now KTM may just “test” something different.
but keep in mind they are just “testing”, there’s no guarantee they are going to switch over completely, nor do they have to. in fact, I don’t think they even have remotely enough data to “cancel Christmas” on the screamer just yet…? they use a different chassis solution from the others so they may be able to make the screamer work, but technically they do need “some” BB data for comparison. the Lemans test I understand was partly cold and wet (shocking) so they definitely didn’t collect enough data on Monday.
if we recall, Duc and Stone won they’re championship with a 90V/screamer/half-trellis combo, but of course that was overtop 16/5 B’stones with Stone piloting so what we have here is a case of one too many variables (Strother Martin voice) thus KTM’s “mileage may vary”.
On point.
Ambitious? What do they have to lose?
Heh, that’s a good point. “I LOVE THIS PLAN!”