2 stroke thread (with occasional F1 relevance!)

[manolis]

Hello Brian Coat

You write:
“In 2016 thermo-structural FEA is not unconventional - it is taught to most / all undergraduates and open source code is readily available.
The trend in engineering is to more CAE prove-out with less/no prototypes and one of the big drivers of this trend is cost.
Would using open source CAE tools (FEA, CFD ...) provide a low cost way to further progress some of your your feasibility studies?”


The shape and the loading of the PatRoVa rotary valve is so simple that the “old way” of calculation is more than adequate.

On the other hand,
if you want to make the thermo-structural FEA of the PatRoVa rotary valve:



be my guest and let me know what you need.

Thanks
Manolis Pattakos

[Tommy Cookers]

Suppose: 50mm stroke 80mm bore (i.e. per cylinder capacity: 250cc)
100mm center to center con-rod 500gr mass of the assembly of piston, wrist pin and top 1/3 of the connecting rod.
peak torque: 110mN at 12,000rpm peak power: 200bhp at 14,000rpm.
At 10,000rpm a conventional four in-line (plane crankshaft) suffers from a free inertia torque of 700mN of 2nd order (it also suffers from a free inertia force of 14,000N (1.4ton), of 2nd order too, but this is another story).
At 10,000rpm, the cross-plane version of the same engine is actually rid of free inertia force and torque.
In the conventional (plane crankshaft) I-4, the rear tire receives the useful torque (the 40mN provided by the engine multiplied by the total transmission ratio), it also receives the useless inertia torque (the 700mN free inertia torque generated by the engine multiplied by the total transmission ratio).
With the typical shape / form of the instant combustion torque provided by the engine, in order to get an average of 40mN torque you need an instant torque varying from, say, -40mN to +100mN, i.e. a total variation of 140mN, while the free inertia torque of the conventional I-4 varies from –700mN to +700mN, giving a total variation of 1400mN (ten times higher).
Think for a second about it: the useful torque (i.e. the combustion torque) passes like noise inside a huge inertia torque that does nothing useful, only friction and stressing of the parts.
A bad thing for the plane crankshaft is that the basic frequency of the combustion torque is the same with the frequency of the free inertia torque. A high frequency torque absorber in the transmission cannot “kill” selectively one of them (even if there were such a shock absorber, by killing the free inertia torque you actually kill a part of the power; think of it).
So, there is a significant difference between the two arrangements.
The drawbacks of the cross-plane I-4 is the uneven firing and the need for an external counter-rotating balance shaft

imo much of the above is wrong for any real vehicle, because ......

much/most of the inertial torques energy is absorbed by the (rpm-maximal) natural oscillatory torsional deflections of the crankshaft
that's the basis of crankshaft design
so the cyclic crankshaft torsional oscillations largely cancel the cyclic rpm variation implied by the cyclic load variations
ie through torsion the crankshaft inevitably behaves as a very high capacity near-lossless energy storage device
by design (for natural frequency) the shaft will necessarily have an oscillation magnitude rather independent of configuration (crossplane or flat)
the flat crank is 4 pairs of webs in series, each pair deflecting simultaneously in the same sense then recovering
the crossplane crank is 4 pairs of webs in series, 2 opposite pairs deflecting etc simultaneously, then so the other 2 pairs 90 deg later
the crank will be designed such that any loss-type damper (if part of the design) would be within its (energy-absorbing) capacity

though even if there was no absorbtion crankshaft rotation would only vary by eg 100 rpm/rev (as crankshaft and conjoined inertias limit this)
corresponding in displacement to only a small total amount of free (backlash), Coulomb-load, and elastic, compliance from crank to road wheel
this compliance will act to inhibit or prevent the propagation of these pulses to the road
that's why the typical lossy transmission shock absorber suffers little (in either the road Yam or the conventional machines)

if these inertial torque pulses reached the road wheel, the tyre would be greatly heated by the internal hysteresis loss


as I have already said, the crossplane crank is a better design for racetrack performance

not because the flat crank causes much more friction
the flat crank's pistons exert from inertia exactly the same sidethrust as the crossplane's and have the same piston friction (5-10% of total power)
not because the inertia forces mysteriously cause energy loss
anyway inertial strain energies with the crossplane crank are about 75% of the flat crank's
(inertias are only summed downstream of the webs - unlike with a V engine's crank)

but because the loads that dominate crankshaft design (for sufficient torsional natural frequency) are evenly spaced in time
so allowing generally smaller dimensions etc and so smaller bearings and reduced bearing friction
this is further helped by the closer angles between consecutive webs giving shorter and stiffer load paths (even some overlap ?)
worth in today's guesstimate maybe 2 hp
and ok, together with the reciprocating inertias contribution, the crankshaft inertia reduction reduces effective shifting time loss

btw 1 - the crossplane crank Urs 4 cyl 500 cc machine won the Sidecar WC in 1968 (and 71)
it seems its creators were looking for less vibration than the traditional flat crank would give (no balance shafts with either, of course)

btw 2 - the 80 x 50 mandated dimensions for Moto GP remind me that in 1958 Ford UK's new (road car) engine was a then-remarkable 81 x 48.5
Cosworth made an industry around this block and/or bore centre from FJ/F3, Touring Cars, F2 1000cc, F2 1600cc FVA, and F1 3000 cc DFV etc
the F2 1000cc showed that with this b:s ratio 2 vertical parallel valves/cylinder were as good as any 2 valve/cylinder dohc hemi
ie there's no benefit in having more valve area than the engine needs
and the engine families (common bore, strokes varied by 60%) clearly show rpm based not on piston speed, but limited by piston acceleration

[Brian Coat]

More from Furasawa-san, Senior General Manager of Engineering Operations, Motorcycle Headquarters, Yamaha Motor Co., where actual measurements are briefly mentioned.

http://articles.sae.org/5586/

Yamaha are not always right (e.g. 5v/cyl ) but they claim to have measured data to support their SNR theory.

[manolis]

Hello Tommy Cookers.

The theory has been already and analytically explained in the previous posts.
I don’t think there is something to be added.
It is simple mathematics. And there is no way “to argue with mathematics”.



Here is a partial quote from the link of Brian Coat ( http://articles.sae.org/5586/ )
It confirms everything the theory predicts.


“His (i.e. Furusawa’s) ideal would have been a multicylinder, even-interval-firing engine with minimum fluctuations in revolutions, thereby getting the maximum amount of propulsion without inducing tire slippage. Ultimately, he added, something like an electric motor.

He said that uneven-interval firing itself was not the primary purpose of his design and development team, but that the 90° crankshaft was a fruit of strenuous work in minimizing fluctuations in engine revolutions. The natural result was that combustion intervals had become uneven because of the crankshaft design.

Furusawa’s team then pushed the uneven-interval-firing envelope to an extreme in one variation of the M1 engine that had all combustion occurring in a single revolution, the “Ultimate Long Bang,” Furusawa described. The exercise produced a change in the bike’s total traction, but no improvement in lap times.

“Whichever the engine configuration may be, inline or V-formation, targeted weight distribution should be no different, about 50/50. It could be a fraction of that at either end, but I am not going into that,” Furusawa said. “I believe the inline engine is more advantageous when fitted within a shorter wheelbase, which is more agile. In the V-configured engine, the rear bank tends to shift the mass rearward, which must be offset by lengthening the wheelbase.”

“What the rider wants is combustion torque proportionate to the throttle work, not inertia torque,” said Furusawa, who drew an analogy to signal-to-noise ratio (SNR), an electrical engineering term. “Combustion torque is a signal, and inertia torque is noise. Unfortunately, noise increases proportionately to the square of revolutions, greatly deteriorating the SNR.”

A typical road vehicle inline four may go up to about 7000 rpm on the high end, which is well within the engine’s effective combustion torque zone. In the MotoGP application, winding to 15,000 rpm, inertial torque would be significant. The rider must make best use of the signal buried deep within a large noise, and that would do no good to the essential connectivity between the throttle and rear tire.

His theoretical SNR graph shows a 180° engine model at wide-open 15,000 rpm, assuming no fluctuations in rpm, in which noise/inertia torque is greater than signal/combustion torque. The compounded torque value that drives the motorcycle is, therefore, reduced. In the 90° crank engine, noise/inertia torque is almost negligible; what little is there is generated by the leaning connecting rods. Net driving torque nearly matches the value of combustion torque and is efficiently transmitted to the rear tire at the rider’s command.

Verification of the Yamaha SNR theory was performed by directly measuring fluctuations in rear tire revolutions during cornering using frequency analysis. In the 180° crank YZR-M1, speed fluctuations by second order in revolutions occurred regardless of throttle opening. The 90° crank version, on the other hand, displayed speed fluctuations of the second order in only 1.5 revolutions when the throttle was opened. Furusawa concluded that the 90° crank engine transmitted the signal/combustion torque singularly and effectively to the driving wheel.

Furusawa recounted racer Valentino Rossi’s first reaction to the YZR-M1 in January 2004. Rossi was the World MotoGP champion in 2002 and 2003, riding for Honda. The young Italian had just switched camps to Yamaha, widely rumored to prove that it was not the song but the singer.
Furusawa put Rossi on both the 180° and 90° crank YZR-M1. On the 180° machine, he commented that it was as power-oriented as his previous Honda mounts. On the 90° crank version, he responded, “Very sweet!” The bike responded precisely to his throttle command, producing optimal rear-wheel traction during cornering, and demanded less physical strain on a long run.

END OF QUOTE



In the first paragraph of the Quote it writes:

“(The) ideal would have been a multicylinder, even-interval-firing engine with minimum fluctuations in revolutions, thereby getting the maximum amount of propulsion without inducing tire slippage.”

If this primary transmission:



were used in a conventional I-4 four-stroke (plane crankshaft, even firing), the inertia torque would not be allowed to arrive to the transmission.
It is a mechanism that, without killing energy, keeps the “bad inertia torque” away from the rear tire.

With the above transmission, the angular speed of the flat / plane crankshaft fluctuates, while the transmission and the rear tire rotate at constant angular speed.

It is the ideal moto-GP engine according Furusawa (the technical director of Yamaha).


I don’t need to see it in practice.
The theory and the mathematics say it works.
Practice will just confirm the theory.

The funny thing is that the gear wheel with the uneven / strange teeth is quite easy to be made with the existing CNC cutting machines (say, with a wire EDM CNC machine). It is a matter of a couple of hours, if you know what you are doing. The other gearwheel is a conventional one.

But who listens?

Thanks
Manolis Pattakos

[gruntguru]

. . . . though even if there was no absorbtion crankshaft rotation would only vary by eg 100 rpm/rev (as crankshaft and conjoined inertias limit this) . . .

Variation in rotational speed due to "inertia torque" would be a fixed percentage of engine speed.

[J.A.W.]

Hello Tommy Cookers.

The theory has been already and analytically explained in the previous posts.
I don’t think there is something to be added.
It is simple mathematics. And there is no way “to argue with mathematics”.



Here is a partial quote from the link of Brian Coat ( http://articles.sae.org/5586/ )
It confirms everything the theory predicts.


“His (i.e. Furusawa’s) ideal would have been a multicylinder, even-interval-firing engine with minimum fluctuations in revolutions, thereby getting the maximum amount of propulsion without inducing tire slippage. Ultimately, he added, something like an electric motor.

He said that uneven-interval firing itself was not the primary purpose of his design and development team, but that the 90° crankshaft was a fruit of strenuous work in minimizing fluctuations in engine revolutions. The natural result was that combustion intervals had become uneven because of the crankshaft design.


“Whichever the engine configuration may be, inline or V-formation, targeted weight distribution should be no different, about 50/50. It could be a fraction of that at either end, but I am not going into that,” Furusawa said. “I believe the inline engine is more advantageous when fitted within a shorter wheelbase, which is more agile. In the V-configured engine, the rear bank tends to shift the mass rearward, which must be offset by lengthening the wheelbase.”


“(The) ideal would have been a multicylinder, even-interval-firing engine with minimum fluctuations in revolutions, thereby getting the maximum amount of propulsion without inducing tire slippage.”



It is the ideal moto-GP engine according Furusawa (the technical director of Yamaha).


But who listens?

Thanks
Manolis Pattakos

Hi Manolis, the really funny thing is, if you 'read between' Furusawa-san's lines, the 'ideal' would be a 2T engine.

Even-firing & even inertia torque impulses ( with lower overall friction/inertia) & able to accommodate
the preferred V-angle engine architecture without concerns for excess wheelbase caused by bulk/mass
of a 4T with many complex moving parts above the piston..

Oh the irony, that such 'politics' causes needless technical problems to negate, & at a great cost too..

[manolis]

Hello J.A.W.

Kawasaki had the idea of the cross-plane crankshaft for the 4-stroke In-Line-Four.
But they had not a “Furusawa”.
So they left the idea unexploited for decades.

Yamaha had “the” Furusawa in charge; he realized the advantages of the cross-plane crankshaft and won several moto-GP championships (with Rossi and Lorenzo).


Suppose that Kawasaki understands the advantages of the “Variable Ratio” primary transmission (previous post), uses it in their 4-stroke plane-crankshaft even-firing In-Line-Four and wins Yamaha that uses Kawasaki’s old idea.

Wouldn’t it be THE irony?

Thanks
Manolis Pattakos

[FW17]

Manolis

When you did the PatRoVa: a disk Rotary Valve with counteracting fronts you used a 4 stroke cylinder with no ports

Supposed if you had used the Rotary valve only for exhausts while retaining the inlet ports in the lower end of the cylinder would you have been able to achieve better results? This would be similar to Diesel 2 stroke but with a rotary valve.

[Tommy Cookers]

Mr Furusawa's idea has not been rigorously established
ok with the flat crank the 2nd order motion apparent in some unspecified part of the tyre appears earlier
but there is nothing directly to show that this reduces the tyre's capabilities, and no such mechanism is suggested
also the idea is essentially opposed to the traditional view eg described by Kevin Cameron as linked by J.A.W

F's claim seems evidenced only from the crossplane engine lapping quickly
this is explicable (as the late Prof Blair's and other firing order work suggests) if the crossplane crank gave a better power curve than the flat crank
F implies/admits that the 'long bang' engine had the best traction ie was in some way better than the crossplane

regarding the ratio of (reciprocation) inertia torque to combustion torque - there's nothing new here (except calling it SNR)
eg Ingham's paper in August 1955 'Automobile Engineer' showed road cars at 4000 rpm having inertia forces greater than combustion forces
eg single cylinder race motorcycles even then had an ('averaged') SNR approaching F's case (eg factory Norton 93x73 c.8000 rpm)
the 'averaged' SNR for a single includes 3/4 of the strokes having an S of zero
(and F says pickup ie from medium rpm is crucial, but conveniently chooses 15000 rpm forces, exaggerating his case)

and remember, eg Yamaha sold 660cc single cylinder machines for the 1993 GP Supermono class
non-GP equivalents of this class are still active with eg 700 cc Rotax singles 103x81 safe to 9500 rpm
and all those other 'big single' dirtbikes and competition bikes ......
these have just as much 'bad SNR' as the 'bad' flat crank engines that crossplane crank Yamahas beat
but their 'bad SNR' doesn't stop them having good traction

remember also that the afaik flatcrank 4 cyl 1000cc Kawasaki dominates WSB etc and the Yamaha doesn't

ok I can see that the emergence of 1000cc MotoGP etc allowed/incentivised unprecedentally small (relative) crank inertia ....
by reduced stroke, 'slipper' clutches (not crank inertia) controlling downturn, and by traction control and self-shifters
(and as mentioned before, the crossplane crank would be smaller and have even less inertia)

so maybe the flat crank 4 did encounter unprecedented problems from this small inertia
but imo not at SNRs that singles or (even-firing) parallel twins haven't used satisfactorily
though also, conventional flat crank 4 cyl F1, Indy and dirttrack etc engines seemed to thrive

[manolis]

Hello Tommy Cookers.

A single has four times stronger combustion torque than a four-in-line even firing of the same capacity.

And it revs at way lower revs (the mean piston speed at the red line is, for racing engines, around 25m/sec).

So, a single cylinder 700cc Rotax (103mm bore, 81mm stroke, 675cc) has a mean piston speed of 25.7m/sec at the 9,500rpm wherein it still runs safely.

A four-in-line with the same capacity and the same “bore to stroke ratio” would have: 65mm bore and 51mm stroke.
For the same 25.7m/sec mean piston speed it runs at 15,000rpm.


Suppose the overall reciprocating mass of the single cylinder (mass of the piston, of the piston pin and of the upper 1/3 of the connecting rod) is equal to the total mass of the four pistons of the four-in-line (actually it is less).

Here is the calculation with the balance.exe program at http://www.pattakon.com/pattakonEduc.htm



So, the inertia torque of the four-in-line even firing is, more or less, equal with the inertia torque of the single of same capacity and same “bore-to-stroke ratio” (both at the red line).
The difference is the third order inertia torque of the single cylinder which is eliminated in the In-Line-Four with the plane crankshaft.

Each power pulse (combustion torque) of the four-in-line is four times weaker than the power pulse of the single.

So, the SNR is four times higher in the single cylinder than in the four-in-line even-firing (4 times stronger signal, same level of noise).


As you see, there is a big difference.
The conventional four-in-line (and the conventional flat four) is the worst arrangement as regards the SNR (Signal to Noise Ratio).
This is so because all the four pistons stop together (at TDC and BDC), and some 90 crankshaft degrees later all the four pistons move simultaneously near their highest speed.
The single of same capacity has four times stronger power pulses, resulting in a 4 times higher SNR.
The twin of same capacity has two times stronger power pulses, resulting in a 2 times higher SNR.

Thanks
Manolis Pattakos

[manolis]

Hello FW17

You write:
“When you did the PatRoVa: a disk Rotary Valve with counteracting fronts you used a 4 stroke cylinder with no ports

Supposed if you had used the Rotary valve only for exhausts while retaining the inlet ports in the lower end of the cylinder would you have been able to achieve better results? This would be similar to Diesel 2 stroke but with a rotary valve.





There is a version of the PatRoVa for 2-strokes.




A problem of the Detroit Diesel shown in the image in your post is that the poppet exhaust valves have to open and close at double rhythm than in a four-stroke engine. If it were a high revving gasoline, the valve train would soon gets into its own “red line”.

Another problem is the lubrication.
As it is now, it is a total loss lubrication.

Quote from http://www.pattakon.com/pattakonPatMar.htm

“The problem as defined in Wartsila's(*) Technical Journal, Feb 2010 ( here http://www.pattakon.com/tempman/Wartsil ... 2_2010.pdf is the full article):
"A slightly more ambitious idea is to apply the four-stroke trunk piston engine cylinder lubrication concept to the two-stroke crosshead engine, i.e. to "over-lubricate" the cylinder liner, apply an oil scraper ring, and then collect the surplus oil, clean it, and recycle it. This will of course be a radical change of concept, and whether or not it is viable remains to be demonstrated, but an outline exists and a patent is pending. The aim is to increase scuffing resistance and to achieve the same low specific oil consumption level as on the four-stroke trunk piston engines."

(*) Wartsila is a global leader in complete lifecycle power solutions for the marine and energy markets

The solution: The PatMar engine applies the four-stroke trunk piston engine cylinder lubrication concept to the two-stroke crosshead engine, i.e. it "over-lubricates" the cylinder liner, applies an oil scraper ring, and then collects the surplus oil, cleans it, and recycles it.
The PatMar not only increases the scuffing resistance of the two-stroke engines, but it achieves the same scuffing resistance as on the four-stroke trunk piston engines.
The PatMar achieves the same low specific oil consumption level as on the four-stroke trunk



End of quote.

The replacement of the poppet exhaust valves of the above PatMar engine by PatRoVa rotary valves would be an interesting solution.

Thanks
Manolis Pattakos

[Tommy Cookers]

@ Manolis
imo your plot (of the single's behaviour) strengthens my view that the SNR concept is a misleading descriptor of the 'Furasawa case'

also F says the Honda RC211V (Rossi's machine before the 2004 Yamaha) had the same driveability issues as the 2003 (flat crank) Yamaha
but the RC211V (5 cylinders at 75.5 deg V angle) would show a 'good' SNR value ? - I guess
(btw - regarding 'downturn' the 2003 Yamaha had 2 of the throttle plates managed for downturn response)


what is happening (with the 4 cylinder flat crank machine) is surely quite simple and has been underappreciated ...... mainly this ......

twice per rev (because of inertia forces) the crankshaft rpm quite briefly and quite rapidly increase and then similarly decrease
these rpm excursions involve piston reciprocational etc energy converting into crankshaft etc rotational energy and vice versa
but the excursions accumulated rotational distance in advance or in arrears of the mean rotation of the rear wheel is quite small
and as the tyre is rather compliant in rotation, any change in tyre thrust at the bead with these excursions is rather small
(also, at this very high frequency of wheel rpm excursion the tyre tread will not follow the tyre bead excursions)

ie the high rate of change of inertia primarily transfers energy into and out of crankshaft (and driveline, and rear wheel) rotation
and so rather little of the calculated inertia effect ('noise') propagates as far as the rear tyre


also there is presumably undamped elastic compliance (quill shaft effect) shock absorbtion functionality incorporated in the power train
this functionality should also have a substantial effect, to further relieve the situation
helping to cancel (inertial load) 'noise' and providing useful smoothing

this having surely having been and now being applied to all machines

and for managing driveability of all machines, they surely also use the electronic systems ?

[gruntguru]

The single of same capacity has four times stronger power pulses, resulting in a 4 times higher SNR.
The twin of same capacity has two times stronger power pulses, resulting in a 2 times higher SNR.

Not sure if you are using the same definition of S/N as Furasawa. I assumed the "signal" he refers to is the average torque output. If so, the power pulses would also be considered as "noise".

[manolis]

Hello Tommy Cookers.

Furusawa of Yamaha followed the correct steps.

He modified a conventional I-4 to cross-plane and asked Rossi to drive both versions.

The basic difference was on the arrangement of the crankpins.

Besides the better lap times, it was also the driver-friendly running (“sweet” running) of the cross-plane that keeps the rider calm (not tired) till the end of the race.

Then Furusawa changed the firing order of the cross-plane to Big-Bang. No improvement.

Then Furusawa tested the idea on the motoGP and took several championships confirming the theory in practice.




According the http://www.sportrider.com/bikes/yamaha- ... stop-watch it seems that Yamaha was so confident about the need for the elimination of the inertia torque (higher SNR), that they proposed a Three-Cylinder Crossplane Engine.

The crankpins are arranged at 0, 60 and 300 degrees while in the conventional even firing I-3 the crankpins are arranged at 0, 120 and 240 degrees around the crankshaft rotation axis.


Is it worthy the I-3-“cross-plane” of Yamaha?
Or it is just an advertising trick, an effort of Yamaha to exploit to the limit the "fame" of their M1 / R1?


Take the 677cc I-4 (previous post) and compare it with a I-3 (same capacity, same bore-to-stroke ratio) having 56mm stroke, 71.5mm bore and 333gr mass of the each piston assembly. The red line is at 13,700rpm (wherein it has the same mean piston speed with the I-4 operating at 15,000rpm).

Here is what the balance.exe program at http://www.pattakon.com/pattakonEduc.htm “says”:



While the combustion torque pulses of the In-Line-4 are 25% weaker than the combustion torque pulses of the In-Line-3, the inertia torque pulses of the In-Line-4 even-firing are 2.7 times stronger than the inertia torque pulses of the In-Line-3 even firing.
The overall SNR (Signal to Noise Ratio) is 3.6 times higher in the In-Line-3 even firing.

Now see the difference of the “cross-plane” In-Line-3 of Yamaha from the conventional even-firing In-Line-3.

According the plot, the maximum value of the inertia torque of the cross-plane I-3 is half than in the conventional I-3.

But the inertia torque of the conventional I-3 is already small.

The cross-plane I-3 is uneven firing.
The cross-plane I-3 is also worse balanced than the conventional I-3 (it requires a pair of balance shafts).

So, is the gain worth the pain?

The reasonable answer is no.



And if you think that with a properly shaped gearwheel on the crankshaft (primary transmission, as described in previous posts) no inertia torque is allowed to pass to the transmission and to the rear tire, neither the cross-plane I-4 (of Yamaha M1 / R1) is “worth the pain” (uneven firing, need for an external balance shaft, extra weight, extra friction).

Worth to mention: the variable ratio primary transmission is not consuming extra energy; on the contrary, it saves energy. Because it deals with the transfer of a substantially weaker torque (only combustion torque passes to the gearbox and to the rear tire).

Thanks
Manolis Pattakos

[manolis]

Hello Gruntugu.

You write:
“Not sure if you are using the same definition of S/N as Furasawa. I assumed the "signal" he refers to is the average torque output. If so, the power pulses would also be considered as "noise".”


Quote from http://articles.sae.org/5586/

“Furusawa _ drew an analogy to signal-to-noise ratio (SNR) _ “Combustion torque is a signal, and inertia torque is noise. Unfortunately, noise increases proportionately to the square of revolutions, greatly deteriorating the SNR.”

End of quote.


According Furusawa, noise is “the inertia torque”.


The SNR should give the ratio of the useful torque (or energy) that goes from the engine to the rear tire (wherein it is consumed, in the contact between the rear tire and the road, pushing the motorcycle forward) to the useless torque (noise) that reciprocates between the engine and the rear tire.

Actually, the inertia torque is not just useless, it is harmful because it adds friction and stressing.

If the combustion torque is added to the denominator of the SNR, then the SNR in the single 700cc, in the Twin 700cc and in the 4-In-Line 700cc (previous post) would be the same.
However in the one case the power pulses dominate (every combustion generates a noticeable push forwards), while in In-Line-4 the power pulses are hidden by the strong inertia torque pulses (the noise).


Reasonably, together with the SNR another number should be given indicating the variation of the combustion torque versus the average torque provided.

Thanks
Manolis Pattakos