How does a cylinder head sound?!

[Frenchbob]

Is this the Hate Harleys thread?......I started reading about how different engine characteristics might be responsible for different sounds, and........!!

 

Actually, I don't particularly like Harleys, either, but Harley owners in France don't seem like a bad crowd, on the whole, and quite often own and are interested in other bikes, too, especially elderly BMWs, Italian and Brit bikes. Vive la difference!

 

My 750S3 makes a sound through its competitzione Lafranconis not unlike a Sportster on open pipes when I let it idle low, as a matter of fact. When I rev it, though, it sounds entirely different.

[Greg Field]

I think a major amount of the H.D. 'character', has to do with it's 45 degree V configuration, along with the single crank pin, giving those engines the "potato, potato' idle, and obnoxious blatt at it's high rev area.

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Guzzi has a single crankpin, too.

[DeBenGuzzi]

Don't bow to peer pressure. If you want one, have one, no need to feel ashamed of your Harley-love.

86127[/snapback]

Its not the peer pressure, its the fact that I know they aren't going anywhere or going to change in any way other than for the good I hope (maybe get more power out of the pigs soon?) and there are lots of other bikes I'd like to try while I'm young. There will be plenty of time for the B roads on a hog when I grow up.

I'm not ashamed but a lot of the harley riders in this area bug the hell out of me, so many buy it for that culture and that is just odd who wants to be known as a loud arrogant jackaninny? I'll wait for more power at a decent price or maybe just build one with a harley frame and a buell engine be hella cheaper than their screamin eagle crap. Big bored engine $6-7K I can get a whole barely used buell for that money, this is starting to sound like a good idea Vrooom!

[Guest Nogbad]

Its not the peer pressure, its the fact that I know they aren't going anywhere or going to change in any way other than for the good I hope (maybe get more power out of the pigs soon?) and there are lots of other bikes I'd like to try while I'm young. There will be plenty of time for the B roads on a hog when I grow up. 

I'm not ashamed but a lot of the harley riders in this area bug the hell out of me, so many buy it for that culture and that is just odd who wants to be known as a loud arrogant jackaninny? I'll wait for more power at a decent price or maybe just build one with a harley frame and a buell engine  be hella cheaper than their screamin eagle crap. Big bored engine $6-7K I can get a whole barely used buell for that money, this is starting to sound like a good idea Vrooom! 

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But the Buell chassis is the best bit! The engine is good though. My race kitted one is smooth and even and fuels perfectly. ! Amazing what Buell have managed to turn the old Sportster unit engine into really.

[mike wilson]

There's another factor. Some time early last century, engine designers discovered an interesting fact: the valves controlling gas flow in and out of the cylinder didn't have to open at the beginning of the inlet or exhaust stroke or close at the end of them. The timiings could be stretched in both directions. Bizarrely, they could actually _both_ be open at the same time at certain points of the cycle. Thus was born the phenomenon known to all and sundry as "valve overlap". Up until then, the gases flowing as and when the designers wanted them to. This was true but some genius realised that it might be better for power production if the gases flowed when _they_ wanted to.

 

With the advent of overlap, we lost the "feeble teufing" of the Ixion books and gained the snarling, popping, roaring beast we know and love. Listen to the difference between a 1903 Werner (a classic "teufer") and a 1950s Rennsport NSU, whose exhaust note has been likened to tearing calico.

 

Apart from the differences in exhaust, I suspect that engine design parameters including V angle and valve overlap will have a profound effect in the eventual noise output of the motor. Not to mention the big nut holding the throttle on.

 

Here endeth the history lesson.

 

mike

[dlaing]

Thanks, Pete.  Best explanation I've heard yet!  

85970[/snapback]

see what I am up against? tag teaming guys that know everything about d i c k.

Just for your information there is a whole other world out there, and it is not all about d i c k.

[dlaing]

It's all relative. 

 

Some people like to go out to the symphony, some like to stay home and listen to the sounds of their own farts.

 

Rj

85988[/snapback]

Thanks, Ryan. Best explanation I've heard yet!

[dlaing]

Don't bow to peer pressure. If you want one, have one, no need to feel ashamed of your Harley-love.

86127[/snapback]

Thanks, Nog. Best point I've heard yet!

[dlaing]

snip

86158[/snapback]

Thanks, Mike. Best explanation (and actually focusing on the topic) I've heard yet!

[mike wilson]

I am _such_ a boring get.....

 

8-)

[Guest ratchethack]

So what IS the stock valve overlap diff. between the HD and the MG?

[Guest Nogbad]

There are significant mechanical differences. Take the base case of a trad Brit 360° parallel twin. Each cylinder fires once per revolution and the TDC firing positions are at the same angle, 0° and 360° for the sake of argument if straight up is 0°. There is therefore a power stroke every 360° of crank rotation.

 

In the Guzzi, the cylinders are displaced 90°. If the first cylinder fires at -45°, the next one fires at 360+45=405° the first one again at 360-45=315° This gives an uneven exhaust beat.

 

In the Harley, the cylinders are displaced by half this amount, and hence the HD engine more closely approximates the even firing intervals of the parallel twin. It fires at -22.5 then 382.5.

 

I would therefore expect the Guzzi to have a more pronounced character than the H-D if it was only cylinder angle.

 

Of course, this only applies to engines with a common crankpin axis. Yamaha made some versions of their parallel twin TRX/TDM engine behave unevenly like a V twin by having crankpins offset by some rotation, I don't know by how much. To me that is a crap idea. At least a 90° V configuration has good primary balance. If you offset a parallel twin you get an horrendous rocking couple set up that would need a second balancer shaft to remove.

[big J]

I dunno about that. Yonks ago I converted a BSA Golden Flash to fire 72deg apart, the crankpins almost being together. I made a new cam to suit. It ran a lot smoother than any normal Gold Flash.

72 deg was chosen cos a pal of mine who was good at maths worked out that the torque "push" from the pistons would be greatest at 72 deg apart.

[Guest Nogbad]

72 deg was chosen cos a pal of mine who was good at maths worked out that the torque "push" from the pistons would be greatest at 72 deg apart.

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Given that in a 4 stroke engine each cylinder fires only every second revolution of the crank, I can't see it. Was the engine set up as a sort of "big bang" split single with the power strokes closely following each other?

 

The standard BSA configuration was like every other Brit parallel twin with both pistons rising and falling together but with firing strokes 1 revolution apart.

[Guest Steve_W]

If you offset a parallel twin you get an horrendous rocking couple set up that would need a second balancer shaft to remove.

There are people cutting and re-welding the cranks of old XS650 Yamaha parallel twins to make them fire like V-twins. The theory, at least, is that with staggered crankpins the pistons are never stopped at the same time, a twice-per-revolution event with a parallel twin, and that itself reduces vibration quite a bit. A better explanation is available here: http://www.sense.net/~blaine/270.html

 

Yamaha did the same thing themselves with the TRX-850 sport twin (sadly not brought to the U.S.). They had a single balance shaft, like the TDM-850 from which they were derived, and I never heard of the TRX being particularly nasty.

 

Also, FWIW, some of the new Bonneville variants are set up the same way, the America and Speedmaster, I believe. They use a single counterbalancer, as does the standard new Bonneville (and Thruxton), and don't vibrate much at all.