what makes twins thump?

[ungeheuer]

And here's me thinking only the Citroen 2CV ran a wasted spark....

Well there ya go.

[DuciD03]

As an unusual side bar:

When building the Coup D’etat (Monster Bobber), I wanted to play around with the sound the bike made, so since a carbed bike runs a wasted spark, I tried all three other cam timing scenarios to see how the bike sounded.  I didn’t run it long this way, just idled and revved a bit.

I phased the V cam only out 180’:  sounded like crap.
I phased the H cam only out 180’:  also sounded like crap.
I phased both cams out 180’: sounded like crap.

I returned the cams to original and it sounded good again.

In case anyone finds this useful....ever....in the history of time....this will be the thread they look for it in, so I wanted to share.

waow;  - this! - above - is what the subject question was / is getting at, perhaps along with the detailed explanations above.

not an unusual sidebar; glad to hear you tested all that out on your own amazing!

… and I wonder if Ducati & Harley & triumph, ural, etc,  made a conscious decision early on in the piston & cam setup with the resultant sound & vibration; etc in the engine design; to make there own unique moto sound that's still with us today; along with performance engineering, that's a part of what makes them unique bikes.
(...interesting to think about how Asian bike design came about too...)

Perhaps the further broader question is "what makes the ultimate moto bike?" ... and the Monster lovers will be in this corner, … and the Harley dudes will be in another corner …. etc,
ha see,
the world IS round!

 

[Duck-Stew]

I didn’t do the cam phasing for any power.  The Bobber runs a ‘W’ headed 900 so it’s almost worthless for power.  The bike is unique so I thought I would try something unique.

I doubt Ducati set timing for a particular sound.  They did it for power.  (I would wager.)

[S21FOLGORE]

<SNIP>
… and I bet Ducati & Harley & triumph, ural, etc,  made a conscious decision early on in the piston & cam setup and resultant sound & vibration; etc in the design; <SNIP>

 

No, they didn't.
Engines are not music instruments.
Engineers are NOT marketing people.

Deep inside their hearts, all engineers are warriors and philosophers.
Marketing people are merchants.

BIG difference.

NO engineers on the surface of this planet will design engine with "exhaust note as top priority".

Whenever the company make that kind of move, it is because the decision was made by marketing department.

Talented, able engineers tend to do opposite thing( performance first, form follow the function kind of mental set), and, as a result, the product sometimes are "failure" from marketing stand point.

As far as motorcycles are concerned, Honda did that more than anybody else.

Excellent idea from the engineering point of view, the market just didn't get it.



Ducati's iconic "L-twin" could have been one of those examples, if it had not been Fabio Taglioni.

Look at the GT750's photo I posted a while back.
Or, this may be even better example.





90-degree "L-twin" layout has some pros, but there are more "cons", inherent cons.

It takes someone(or group of people) who's really creative and passionate, committed to his own creation, to make things work.

Other example?

Much less exotic, and much less famous, but Honda CX (GL) 500's V-twin was, (still is) amazing example of what
really passionate engineers can do.
(IF you know anything about how to design an engine for mass production, you can easily see why this is so amazing.)

[Duck-Stew]

Remember, it’s a high performance motorcycle & not a musical instrument.

[diamonddog-2]

Jiminy Cricket!,  .....  you guys know a thing or two about a thing or two.

A Ducati guy once told me that the L twin cylinder configuration on a Duc was closer to the V-8 engine configuration and that's why, at least partially, the Duc engine has the "throatier" sound vs. V twin?

My 2 cents is the noticeable exhaust note difference between a single pin crank on a V twin and a dual pin crank. The single pin crank has that distinct "potato-potato-potato" exhaust note  vs. the less desirable exhaust sound from a dual pin crank on a V twin.  Honda made the Aero 1100 [ a stylized Shadow ] from 1998 to 2002. They went from a single pin crank to a dual pin in 2001. Big "sound" difference between the 2. Smoother engine with a little more power on the dual pin crank but no potato exhaust.  I don't know if they ever used a single pin crank on any of the other V twins.

...anyway, great topic and information.

[S21FOLGORE]

<SNIP>They went from a single pin crank to a dual pin in 2001. Big "sound" difference between the 2. Smoother engine with a little more power on the dual pin crank but no potato exhaust.  I don't know if they ever used a single pin crank on any of the other V twins.

<SNIP>

Yes, there was.






Offset dual-pin crank was first used by Honda, for reducing the vibration of narrow angle V-twin.

90-degree v-twin (that includes Ducati "L" - twin) has ONE major advantage over other configuration.

What is it ?

ZERO primary vibration, that's what it is.

Reciprocating engines have inherent balancing problems.

It comes from the fact that you have to convert reciprocating movement of the piston(s) (back and forth in line) to rotating movement (going round and round).

So, 90-degree V-twin is free from primary balancing problem, meaning it can rev freely without balance shaft (which adds weight, production cost, saps power) to higher PRMs.

When the engineers choose 90-degree V, that's the main reason.

Saying some hing like they had chosen that configuration for the sound is actually an insult to Taglioni.


"Free from primary balancing problem" was the reason Honda used 90-degree, on this one.

So which engine was it (the picture on top)?

...I have to go for now. I just moved, have tons of stuff to do ... will come back later.

[S21FOLGORE]

1983 Honda VT250F

This engine was in production up until 2017.
(The V-twin that red zone starts at 13,000RPM.)
It had been in production for 35 years, virtually unchanged.

In the early 80s. Honda was actually ready to ditch all their inline-4 series, and move onto "90º V" engines.
The first ones were V45 Sabre and V45 Magna, in 1982.

V45 Sabre


V45 Magna


They were 90º V-4. All of their new "V" engines were 90º, because of the primary balancing I explained in the last post.

Look at the Sabre and Magna's side view photos above carefully.
Then, look at these.


VT250F 1983


VTR250 2006



Pay particular attention to

1) Where crankshaft is located (where the engine is mounted)

2) Front fork Caster angle (rake angle)

3) Wheel base (How long does the bike look like)

Now, this,

1978 Ducati 900SS


Put a rider on,
now, can you see the "biggest con" of "Ducati L-twin"?

[S21FOLGORE]

Keira Knightley is 5'7", and look how she's stretched out on a bike.



Actually, this could be her stunt double ...hard to tell ...  but it doesn't matter.

The point is, ... can you see the biggest problem of "L" twin layout?

Look at V45 Sabre's side view again. Notice the engine is tilted forward, like Ducati's L-twin, whereas VT250F's engine is more conventional "V" layout?

"L" layout, front cylinder almost parallel to the ground, severly limit the chassis design freedom.

Because the front cylinder is sticking out forward, the engine must be mounted fairly far back, and the front forks are raked out in order to clear the cylinder.
That, inevitably makes wheel base longer.
(750 / 900SS wheel base 1500mm / 59 - inch,
    V45 Sabre wheel base 1562mm / 61.5-inch)

You can't mount the engine forward, like Buell.
Also, look at the difference in caster angle.
Buell like front end geometry is simply impossible with "L" layout.

The engine must be mounted in certain location, there's no room to move it forward / backward.
That forces you to make wheel base (and over all length of the bike) longer.
That forces you to put more cater angle to the front end.

So, why "L" layout was chosen?

If it (the engine) is tilted back (like most other 90º V engines, like VT), the chassis design would be much easier.
Or, it the angle of V bank is narrowed down, again, that would make everything so much easier.

So, the question is,

1)Why did it have to be 90º V-twin ? Not 45º, not 75º, BUT 90º? and "V"?
2)Why did it have to be tilted forward ("L" layout)?

There's a reason.
And it has nothing to do with exhaust sound.
(The distinctive exhaust note was simply a by product.
NO engineer would design an engine / vehicle in order to produce "nice sound".)
"
There are two key points, about choosing "V", not just any "V", but "90º V".
The more you get into engineering, the more "90º V" start looking like ultimate configuration.

One is primary balancing nature of 90º V.
The other is driveability, or, should I say, "traction" (tractorbility), especially coming out of the corner.

[S21FOLGORE]

Let’s go back in time, to 1902, for a moment.

When Harley-Davidson decided to choose 45º V-twin,
Was that a mistake from engineering point of view?

No. Not at all.

Did they do it for the sound?

Absolutely NOT.

Looking at pros and cons of 45º V-twin, it was perfectly understandable decision, and “cons” weren’t really cons, given the situation back then.


Pros of 45º V-twin

Relatively simple and easy to mass produce
(Not just the number of parts. The more time it takes at assembly line to assemble, the more expensive it gets.)
Better performance than single
Easy to design the chassis, or easy to fit into the existing chassis.

Cons

Vibrations, just as bad as singles
Because of the nature of being massive vibrator, it won’t rev up to higher RPM.



Cons weren’t really cons, back then.
And, … they weren’t, even after 40 years.

Harley Davidson WLA 1942



These side-valve 750cc v-twins tops out just a little bit over 4,000 PRM.

Transmission has three speed. And, shift change by HAND.
(The clutch is on the left foot board.)

On top of that, there's no CDI, no automatic ignition advancer back then.

You'd have to manually advance / retard the timing, while you are riding.
(U.S. Army's operating manual calls it "spark grip", which is on the left hand grip.)




You are not revving it up to 10,000RPM, quickly shifting through closed ratio transmission.

45 degree V-twin was still NOT a mistake, by any means.

And, they (H.D. and U.S. Army) didn't choose that layout because of the sound.

[S21FOLGORE]

Fast forward to 1969.
In order to understand the engineer’s thinking process, let’s pretend you are Fabio Taglioni, in the late 1960s.
So, you are the chief engineer / technical designer / director, for this company.
I’m not going to write the history of Ducati motorcycle from 1947 Cucciolo to the late 1960s. You can find the story about them on the net easily.



Instead, I’m going to explain, HOW the engineer’s mind work, when making a big decision, such as choosing engine layout.

Your job, this time, is to sketch out the bike for the next production run.

There are (roughly) two big things you need to keep In mind.

ONE: Ducati was in pretty bad financial trouble, at that time. (In fact, they were owned by Italian government since 1969.)

TWO: Japanese bike's domination, on both racing and street, had already started.

1969 Honda C750 Four


Honda CB750 Four already hit the market, practically sweeping away British twins such as Triumph , Norton which were the king of big sport bikes.
The company (Ducati) wanted / needed new model, in bigger displacement (a lot of it had to do with exporting to US market), and (preferably) something can be turned into production racer. (In other word, NOT a cruiser bike, they needed / wanted high performance sport bike, in 650 – 750 cc range.)
So, you have to put performance on top of the priority list.
The company needed something that performs good,
NOT something that sounds cool.

Since the company never produced the bikes in this class, you’d have to start from the scratch.

First, you need to decide the engine layout.

Single is out of question, since you are aiming at 750cc class. (And you're pretty sure, later on, it will be expanded to sub 1-litter class.)
(Technically, 750cc single is possible, but there’s no benefit. At that engine displacement size, the negatives outweigh the positives (of the single cylinder). Forget about sub 1 litter single engine.)

How about inline 4 ? , or, even, inline 6?
(Taglioni designed 4-cylinder, 8-cylinder,…. He had tons of experience.)

Well, you, and the market have already seen CB750 Four.

You (and the public) also have seen Japanese multi cylinder race bikes

1966 Honda RC166

250cc inline 6 that revs 20,000RPM


Mike Hailwood on RC166


No, you don't want to do inline-4 (or 6) the company have seen all of these. (And that’s why they abandon the idea of competing in small (250cc, 350cc) class racing.)

You know other Japanese manufactures will follow.

You know outperforming those Japanese inline 4 (or 6 ) with the “same layout” would be next to impossible.

You know the company (Ducati) needs something really special, to stand out in the market.

AND, (this is very important), that SOMETHING SPECIAL has to be, … something that can be brought into reality WITHOUT too much trouble.
Remember, the company IS in DEEP financial trouble.
Investing in new factory line and facility, that’s a pretty big gamble.
The last thing you want to do is to choose the engine layout because it sounds good.
(I’ve got to go to work now.)

[DuciD03]

yep Tangolini  designed by Miguel Angel Galluzzi, by Ducati in Bologna, Italy, in 1992. A naked bike, characterized by an exposed engine and frame, he created a (somewhat) unique bike design with the Monster; that fit the times; showing the trellis frame & Ducati desmo L twin along with some unique and decent performance and handling characteristics, with a resultant unique Ducati thump and chatter of a dry clutch; and not saying this is a a musical instrument; being a bit fachious (sp!? ok facetious!); but when you hear that sound, you look to see what Duc is being ridden; and yes of course performance would take precedence over the sound, but interesting to hear how the firing sequence, piston layout influences the sound. "Si, capisco?".

Mostro in Italian; is the naked bike designed by Miguel Angel Galluzzi and produced by Ducati in Bologna, Italy. It is a naked bike, characterized by an exposed engine and frame.

ok; always got to be on your toes with the dmfers,  I stand corrected; got the wrong guy; I ws close  

[S21FOLGORE]

Taglioni didn't design Monster.

What Monster was to Cagiva / Ducati was, what 240Z was to Nissan.



(I've got to run now)

[ducpainter]

Galuzzi designed the Monster

[S21FOLGORE]

Yup.
Some of you may not know, but Ducati Monster was very unique from the  very beginning, even before it was born.


One
They were both tremendous financial help to the companies.
Very, very low developing cost and great success in sales means HUGE profit for the company.

In fact, because of Monster’s success, Ducati was able ot pay off their debts.

TWO
They (240Z and Monster) were both cheaply put together “(existing) parts bin special.”
From engineering / technological point of view, there’s NOTHING to look at, on both vehicles.
Engine, frame, running gears, … everything is borrowed from the existing model.
Nothing new to develop = HUGE money (and time) saving


THREE
“Looking good is primary, everything else is secondary”
In both cases, “styling” was the most important key.
They guy who designed the 240Z’s body line had to work really hard.
The “long nose, short deck” classic sport car body design was the most important element of the project.
However, L24 engine is just too tall to fit into the original sketch body line.
(Can you see how the cylinder head is sticking out?)



The only way to solve the problem was to raise the engine hood, but it would destroy the elegant body line flow.


In the end, they came up with the idea of raising only the center portion of the hood, just enough to clear the cylinder head.





Yes, the hard work was NOT about developing the functional parts, but to keep the styling close to the original concept sketch.



Fast forward to 1992.

Ducati Monster concept sketch by Miguel Galluzzi





His famous quote
“All you need is: a saddle, tank, engine, two wheels, and handlebars”
(His design philosophy about Ducati Monster)

In order to bring this concept to the reality, the approach they took was the true “MAD MAX” style, “A bit from here, a bit from there …”



The frame from 888, the engine from 900SS, the front end from 750SS, …

Read his design philosophy again.
What do you need to enjoy the ride?
By 1990, Ducati had already established the “brand image”.
Unfortunately, that “brand image”, at least part of it, was deeply connected with snobbism.
So, those (some of )Ducati enthusiasts were MAD, at this cheaply put together (that’s how it looked to them) Frankenstein style parts-bin special bike.

BUT, that’s exactly why Monster became successful, that’s why it was, and still is, so unique.

IF the motorcycles were human, the superbikes, such as 916, Panigale would be serious athletes, who are on mission, to win the competition, to set the record.
Monster would be the guy who’s with a lot more relaxed attitude, having fun and looking good is far more important than seriously practicing sport.

Think someone like Fonz.



Or, think Superbikes are temperamental supermodels.

And Monster as, someone like Mary Stuart Masterson in “Some kind of wonderful (1987)”