what makes twins thump?

[DuciD03]

 

(ok... I know this is a question like …"why is the world round" … not flat;) (... not your twin chick fantasy, sheesh)

what makes twins, L twins, V twins and larger singles thump?

… form some limited experience, and what I know; is it the low compression pistons? or the size of the pistons or the rpms that its running at?  I wonder how much R&D time Ducati put into exhaust note tuning? Like the s2r udder.

… a high revving jap bike is more like a sewing machine with a propeller ready for takeoff when wound up, at idle like a  a quiet purring?

[S21FOLGORE]

<SNIP>
what makes twins, L twins, V twins and larger singles thump?
<SNIP> is it the low compression pistons?

No

or the size of the pistons

In case of big single, (sort of ) yes
)

or the rpms that its running at?  

No.

What you are feeling (the difference between inline 4 engine bikes and big twins) is mostly due to the firing sequence (intervals).

In case of inline four, the firing interval is 180 degree.
In other words, while crankshaft turns twice (720º), camshaft would turn once, firing all four cylinders once.
Every 180º of crankshaft rotation, one of the cylinders fire.

With inline six, such as CBX or KZ1300





Every 120º of crankshaft rotation, one of the cylinders fire.

Twins are, somewhat unique. (And, maybe somewhat complicated, to some.)

Ducati L-twins,

1) Horizontal cylinder fires

2)crankshaft turns 270º, then Vertical cylinder fires

3) crankshaft turns 450º, then Horizontal cylinder fires

The firing sequence of Ducati L-twins is uneven.



Firing of inline 4 is like,

BANG - 0 - BANG - 0 - BANG - 0 - BANG - 0 -
(Between "0" and "BANG" is 90º crankshaft rotation. So, above sequence shows one cycle of the engine, which means crankshaft rotate twice = 720º)


Ducati L-Twins are like,

BANG (H) - 0 - 0 - BANG (V) - 0 - 0 - 0 - 0 -

(You can count the number of hyphen, to know how much crankshaft turns. Between the firing of H. cylinder and V. cylinder, there are  three hyphens, so 3 x 90º= 270º, after firing V. cylinder, there are five hyphens before next firing of H,Cylinder, so 5 x 90º = 450º

As you can see, in one cycle of the engine (crankshaft turns twice), on Ducati L-tiwns

there are only two "BANG"s, and they are widely spread apart, and the interval is not even,

as opposed to four "BANG"s at every 180º of crankshaft turn.

The power delivery is smoother, the sound would be more even, ... you get the picture.

Okay, I have to go to bed now.
(It's 2:14 AM now.)






I wonder how much R&D time Ducati put into exhaust note tuning? Like the s2r udder.

… a high revving jap bike is more like a sewing machine with a propeller ready for takeoff when wound up, at idle like a  a quiet purring?
[/quote]

[stopintime]

.... they wouldn't be thumpers if they didn't 

[Charlie98]

The real question is why a Ducati 'thumps' but a Harley 'potatos'...

[Speedbag]

The real question is why a Ducati 'thumps' but a Harley 'potatos'...

The 45* angle of the V, primarily, which dictates that the cylinders fire at odd intervals.

I refer to the Harley sound as the Engineered Miss. And I'm somewhat of a Harley guy. The sequence is:

A piston fires. The next piston fires at 315 degrees. There is a 405-degree gap. A piston fires. The next piston fires at 315 degrees. There is a 405-degree gap. Etc.

[S21FOLGORE]

What you hear as the difference between the bikes is mostly the variations of firing intervals, NOT the number of cylinders.

Harley's firing interval is 405º then 315º.

1) The rear cylinder (HD calls this as #1 cylinder) fires

2)cranks shaft rotates 405º, then front cylinder fires

3)crankshaft roates 315º, then rear cylinder fires again

DOF .....DOF ...DOF .....DOF...

... actually, their firing interval is more even than Ducati's.

The reason you feel like HD sounding like more irregular firing order,
while in fact Ducati engines are more irregular firing than HD,
is because

1)You hear HD running at lower RPM than Duc.

2)That (low RPM nature) mostly comes from 45º (narrow angle) "V" bank.

At 45º, you really can't make them revving up high.
(Both pistons come to TDC fairly close together.)

BTW, the earth shaking big vibration nature of HD also comes from this.
Imagine two  big & heavy pistons moving up and down almost at the same time, right front of you.
(Riders would feel "up & down" vibration A LOT MORE than "front to back" vibration.)

Okay, I have to go to work.

[Charlie98]

If memory serves, Honda, I believe, when they introduced the Shadow V-twin... in typical Honda fashion, they engineered the motor for the best performance, the firing interval took the 'potato' out of the equation.  I guess they did some market research and decided they had to engineer the 'potato' back in to draw the cruiser V-twin crowd to the bike.

[DuciD03]

ah ha!

… the world is not flat!

and ...omg … some guys know a lot of shit!  
(and assuming you's didn't pull that shit off a google search)

so, Harley's potato IS an engineering mistake?! or an anomaly that couldn't be avoided; in a mistake that couldn't be avoided... in a 360 degree round world; of firing sequences …  im just trying to understand … ya, now that its explained, I see how you feel the Harleys pistons.

so from s21folgore's explanation, with thanks;

ok; … Harley's firing interval is 405º then 315º = 720 … in a 4 stroke sequence ....

interestingly;
Ducati L-Twins are like,

BANG (H) - 0 - 0 - BANG (V) - 0 - 0 - 0 - 0 -

(You can count the number of hyphen, to know how much crankshaft turns. Between the firing of H. cylinder and V. cylinder, there are  three hyphens, so 3 x 90º= 270º, after firing V. cylinder, there are five hyphens before next firing of H, Cylinder, so 5 x 90º = 450º
…. = 720
cylinders being oriented at H 270 and V 20 degrees necessitating this crank turning and firing sequence?


but we're hearing that thump from the exhaust, due to the overall size and stroke of the piston?; right? or is it due to a 4 stroke sequence? with just 2 cylinders?

… ach! alas …. the word is flat ...  

[S21FOLGORE]

If memory serves, Honda, I believe, when they introduced the Shadow V-twin... in typical Honda fashion, they engineered the motor for the best performance, the firing interval took the 'potato' out of the equation.  I guess they did some market research and decided they had to engineer the 'potato' back in to draw the cruiser V-twin crowd to the bike.

I believe what they (Honda) did was to change the amount of dual crank pin offset for US market.

At around that time (or shortly after) Harley was trying to "copyright" that "potato -potato" exhaust sound.
Yes, it's pathetic. But they were trying to just about everything getting copyrighted and trade marked.
(Another pathetic attempt was to get "black and orange color scheme" copyrighted.)

From the business point of view, that move was somewhat understandable.
When it comes to things like Harley, people pay money for an image.
Not for the performance, or build quality of the stuff, or excellence in engineering.
You don't need an engineer.
All you need is lawyers and marketing people.

[S21FOLGORE]

<SNIP>
so, Harley's potato IS an engineering mistake?! or an anomaly that couldn't be avoided; in a mistake that couldn't be avoided... <SNIP>

This is going to take some time.
So, let's try one by one.

About Harley's 45º "V" angled engine.
Why did they choose 45º, instead of, for example, 90º like Ducati?

You have to go back to 1909.

Harley's first V-twin engine motorcycle.



The "45º V" configuration was a result of trying to fit an engine into a bicycle style frame and make it work.



Ducati's first "L- twin" motorcycle was 750GT, 1970.



Ducati's L-twin bikes were intended for racing / sport riding purpose from the very beginning.

They way they were borne, there's a big difference in time and background.





Relationship between the 'V angle" and firing sequence of V-twin single crank pin engine (Bothe Ducati and Harely engines are single pin)

360 - angle of "V" = first cylinder's firing crankshaft angle
360 + angle of "V" = second cylinder's firing crankshaft angle

For example,
45º V-twin Harley

360 - 45 = 315º
360 +45 = 405º

60º V Rod

360 - 60 = 300º
360 + 60 = 420º


Ducati 90º

360 - 90 =270º
360 + 90 = 450º

[Speedbag]

Folklore also has it that the 45* layout of the H-D twin is due to it being based on radial aircraft engines of the time, some of which also had 45* cylinder angles. Internal construction with the fork and knife connecting rod arrangement is also similar. It's easy to simply see the resemblance too. 

[Charlie98]

At around that time (or shortly after) Harley was trying to "copyright" that "potato -potato" exhaust sound.
Yes, it's pathetic. But they were trying to just about everything getting copyrighted and trade marked.

I remember that as well... they were on a serious attempt to shut down the competition.  Funny how things change.

[S21FOLGORE]

<SNIP>
(and assuming you's didn't pull that shit off a google search)

<SNIP>

Very good point.

I actually wrote about this type of online article (The writer doesn’t know about the subject. The article is written based on minimal online search. )
http://www.ducatimonsterforum.org/index.php?topic=42312.msg1416859#msg1416859






Myth :Harley’s V-twins don’t rev high, are not smooth running because of uneven firing sequence. Ducati’s L-twin revs higher and smoother at higher RPM because 90º V-twins have even firing sequence.

Truth: I already wrote in above post.
Ducati’s firing sequence is even more irregular than Harleys.


Myth : Ducati’s engine can rev up to high RPM because of desmodromic.
Truth : Desmodromic doesn’t make engines being able to rev high. The advantage of desmodromic  is that it prevants valve-surging at higher RPM.

[ungeheuer]

No

In case of big single, (sort of ) yes
)No.

What you are feeling (the difference between inline 4 engine bikes and big twins) is mostly due to the firing sequence (intervals).

In case of inline four, the firing interval is 180 degree.
In other words, while crankshaft turns twice (720º), camshaft would turn once, firing all four cylinders once.
Every 180º of crankshaft rotation, one of the cylinders fire.

With inline six, such as CBX or KZ1300





Every 120º of crankshaft rotation, one of the cylinders fire.

Twins are, somewhat unique. (And, maybe somewhat complicated, to some.)

Ducati L-twins,

1) Horizontal cylinder fires

2)crankshaft turns 270º, then Vertical cylinder fires

3) crankshaft turns 450º, then Horizontal cylinder fires

The firing sequence of Ducati L-twins is uneven.



Firing of inline 4 is like,

BANG - 0 - BANG - 0 - BANG - 0 - BANG - 0 -
(Between "0" and "BANG" is 90º crankshaft rotation. So, above sequence shows one cycle of the engine, which means crankshaft rotate twice = 720º)


Ducati L-Twins are like,

BANG (H) - 0 - 0 - BANG (V) - 0 - 0 - 0 - 0 -

(You can count the number of hyphen, to know how much crankshaft turns. Between the firing of H. cylinder and V. cylinder, there are  three hyphens, so 3 x 90º= 270º, after firing V. cylinder, there are five hyphens before next firing of H,Cylinder, so 5 x 90º = 450º

As you can see, in one cycle of the engine (crankshaft turns twice), on Ducati L-tiwns

there are only two "BANG"s, and they are widely spread apart, and the interval is not even,

as opposed to four "BANG"s at every 180º of crankshaft turn.

The power delivery is smoother, the sound would be more even, ... you get the picture.

Okay, I have to go to bed now.
(It's 2:14 AM now.)






I wonder how much R&D time Ducati put into exhaust note tuning? Like the s2r udder.

… a high revving jap bike is more like a sewing machine with a propeller ready for takeoff when wound up, at idle like a  a quiet purring?

Awesome

[Duck-Stew]

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.