Harley Davidson motorcycles . . . . .

[Cyberian]

Anyone know why they have that odd, distinctive rhythm espescially at idle?

I don't need any HD, bike or biker bashing right now.
I just want to know about engine/exhaust dynamics.

 

[GasX]

The engine is a V-2. The pistons are not connected to the crankshaft 180 degrees from each other, so the engine does not have a symmetric cadence. When they aren't too loud, it's a beautiful sound.

 

[Urinal Mint]

I think it's the way the cams are set up, but don't take that as gospel.

 

[Zenmervolt]

I'm not at all certain of this, but I have heard that Harley's are basically 1/9th of a rotary (NOT wankel, an otto-cycle rotary, like in the P47 in WWII). This means that both pistons share a single attachment point (for all intents and purposes) to the crankshaft, which cause both cylinders to fire quickly in succession, then a lull until the pistons come around again. This would put the dynamics near those of a single cylinder (I think). As I said, i'm not ceratin of this, and I am curious to know if it is correct.

Zenmervolt

 

[GasX]

I don't know if it is a single attachment point or near to it, but you have the right idea.

boom boom <pause> boom boom <pause>

 

[Moonbeam]

A computational fluid dynamics analysis of an engine exhaust/test cell/diffuser combination can be presented. The full Reynolds-averaged Navier-Stokes equations are solved by application of a Beam-Warming algorithm on a numerically generated, body-fitted computational grid. Axisymmetric numerical results and correlations with experiment may be presented for a high-bypass .... engine and for a subscale model also. Correlations with experiment can indicate that the current solution technique provides both a qualitative (overall flow field) and quantitative (surface pressure distribution) analysis capability for engine exhaust/test cell/diffuser flows including test cell recirculation. The results presented indicate a potential for applying this technology to the assessment and correction of test cell effects in high-bypass engine testing and sound charactic determination. It's very simple really.

 

[Pliablemoose]

I believe it's because of a staggered crankpin arrangement...

 

[BreakApart]

Odd, distinctive rhythm? Compared to what?

The Harley is a V-twin -vs- most rice-rockets that are inline-4s.
The popular Harleys generally have more cc-(1300-1500, where inline-4s have 600-1100)
They do make smaller cc Harleys, but they are rather wimpy sounding.
An inline-4 fires 4 times in the same time a V-twin only fires 2, so the sound waves are closer together and tend to reflect off each other, where the V-twin has pauses.
So the engine has larger cylinders than inline-4s, thus you get a deeper tone. Compare a chevy 350 -v- Chevy 454, much deeper sound. An inline-4 with straight pipes makes a lawnmower type &quot;bap bap bap&quot;, where the V-twin makes the &quot;thump thump thump&quot;.

Suzuki makes a few V-twin sport bikes, and with a nice exhaust, sound sweet.
Here is a link, the exhaust clip is a Suzuki SV650 with a Renegade single exhaust pipe.


Sound Clip-on Renegade home page
Link to a picture of this sport bike-> SV650 with renegade exhaust

 

[Cyberian]

Thanks, moonbeam !

(what was I thinking??)

 

[BreakApart]

Moonbeam,
Thanks for explaining how a turbofan engine exhaust works.

Now can we talk about V-twins please.

 

[GasX]

BreakApart - the question was about the cadence not the tone.

Most internal combustion engines no matter how many cylinders are designed to have cylinders firing evenly throughout the cycle.

e.g boom boom boom boom boom.

The Harley engine does not do this. It fires both cylinders in rapid succesion and then there is a pause until they fire again. It is a VERY unique sound and only harleys have it.

 

[Moonbeam]

 

[Tripleshot]

>>Anyone know why they have that odd, distinctive rhythm espescially at idle?<<

It's to create spontanious orgasims in jiggly breasted, small minded women, and Harley owners know it. It's all about the women,bubba. No other reason. Sex sells.

 

[GasX]

Moonbeam - do you factor octane emmision into the Navier-Stokes equations or do you wait until you apply the vector differential in the Reynolds iteration?

 

[Moonbeam]

Yes I do.

 

[Red Dawn]

<< It's to create spontanious orgasims in jiggly breasted, small minded women, and Harley owners know it. It's all about the women,bubba. No other reason. Sex sells >>

Sheer Genius

 

[Urinal Mint]

<<

<< It's to create spontanious orgasims in jiggly breasted, small minded women, and Harley owners know it. It's all about the women,bubba. No other reason. Sex sells >>

Sheer Genius >>


You don't see many chicks crawl on a rice burner for this precise reason.

That, and they probably don't want to meet death head-on.

 

[GasX]

combine that with the &quot;If you can read this the bitch fell off&quot; T-shirts and you can see why Harley riders are a breed apart.

 

[BreakApart]

Ok, i thought my explaination was funner. (not funny like moonbeams though)


Answer: 45* V-twin (boring isn't it)

Example:
cyl-1 fires, waits 45* crankshaft rotation, cyl-2 fires, now must wait till the crankshaft rotates 315* till the cycle starts over again.

Boring isn't it...

 

[BoberFett]

Zenmervolt has the best explanation, AFAIK, and Tripleshot has explained the motive behind the science.

 

[GasX]

45 degree v-twin - that's the phrase that was dancing around in the back of my mind.

that is exactly what it is.

 

[SammyBoy]

breakapart a 4 cylinder car doesnt fire all 4 pistons at once!

 

[Fausto]

Side note: Harley actually tried to get their &quot;sound&quot; patented. Sheesh.

If you'd like to hear a really neat sounding engine, check out the Benelli Tornado

site

Fausto

 

[BreakApart]

Sammyboy,
I fail to see where you thought i ment, or even said anything like that?

I explained the sound/cadence is caused by timing. 45* engine, 360* full-crankshaft turn, thus a 45* engine forces each piston to fire 45* apart, then a long pause before it begins again-approx 315* pause...


A 4 cyl engine:
Inline-4 = 360* full-crankshaft turn, thus (1) piston fires at approx every 90* of rotation. This leads to a balanced sound.
V-4 would/could either balance and fire (1) piston every 90*, or (2) every 180*.

 

[Moonbeam]

I tool a look at the new Indian motorcycle store in Redwood city yesterday. Fun. The side car models are way cool.

They have a very Harley big bike sound, I thought.