Interesting debate how a Vulcan V-twin is different than a HD V-twin

[hayes]

The original hd was made from a 10 cylinder plane engine. You get that sound because the crank is still based of ten cylinders. You get fire on 1 then 2 but then you have 8 missing fires. That's the "hesitation" you're hearing.

I was told that by a Harley historian and it made sense. I have no idea if it's true, but I believe it...

[ubernomad]

Originally Posted by hayes

The original hd was made from a 10 cylinder plane engine. You get that sound because the crank is still based of ten cylinders. You get fire on 1 then 2 but then you have 8 missing fires. That's the "hesitation" you're hearing.

I was told that by a Harley historian and it made sense. I have no idea if it's true, but I believe it...

That makes no sense to me. It's a 4-stroke engine. You wouldn't have 8 missing firings unless they purposely skip power strokes by disabling spark or fuel.

[Jllm02199]

Originally Posted by ubernomad

That makes no sense to me. It's a 4-stroke engine. You wouldn't have 8 missing firings unless they purposely skip power strokes by disabling spark or fuel.

On Harley both cylinders fire on the same cycle. 45 degrees apart.

[Navigator]

Very interesting thread. Historically the "potato-potato" sound described the panhead/shovelhead. My 78 FLH shovel had a distinctively different sound than my 1988 Evo Electra Glide and my present 2002 Dyna Twin Cam 88. All have that common "hesitation" and all sound great. An old Harley guy can recognize the sound of a shovel starting up and idling without seeing it. The Evo and TC not so much. And unlike the Evo or Twin Cams, the shovel can idle at a lower RPM without the possibility of engine damage which somewhat contributes to the difference.

I am curious about the firing sequence discussion. I installed a Crane Hi-4E single fire coil on my Evo and expected it to change how it idled and sounded. It did not. Now I'm curious.

As an aside, the 2-1 Thunderheader for my Dyna Super Glide arrives Thursday and I'm looking forward to see how it sounds and performs.

[andyvh1959]

Originally Posted by Jllm02199

On Harley both cylinders fire on the same cycle. 45 degrees apart.

Yes, but, no. The cylinders are 45 degrees apart, and on a "dual spark or wasted spark" ignition system both plugs fire together but not 45 degrees apart. The combustion stroke of a 4-cycle v-twin with dual/wasted spark ignition, and a shared air/fuel intake system is what creates the sound. Some say the valve system has influence on the sound. Nope. 2-valve or 4-valve heads, pushrod valves or overhead cam valves heads have no impact on the sound.

Its the odd firing order of a Harley; 1st cylinder combusts the air/fuel mix and 315 degrees of engine rotation later the 2nd cylinder combusts the air/fuel mix. In between is the partial combustion we can hear during the wasted spark in the cyclinder with the exhaust valve slightly open. That also creates a sound pulse in the intake. So we can hear each specific combustion event out the exhaust. That, and the fact that many Harleys get that air/fuel mix into the cylinders through one shared intake system, whether that's one carb or one fuel injector. On a 45 degree v-twin it is tough to package two carbs, two intake runners, or two FI throttle bodies between the cylinders. Spread the cylinders out a bit, 50 degree VN1600 or 52 degree VN1700 and there is more room for dual intake systems. Also, water cooled v-twins don't have the required large diameter cooling fins. Vulcans have fins on the cylinders (mostly for looks), but the diameter is much smaller, allowing room for carbs or throttle bodies.

But a Harley, 45 degree v-twin, with two carbs, nothing else changed sounds unique to the same 45 degree v-twin with one carb. The sound of a twin air intake 45 degree Harley is much closer to the sound of a VN1600:

Here is an easy way to compare the sound difference:
1st, stock Harley one carb:
2nd, piped Harley XR1200:
3rd, Harley XR1000 two carbs:


Now, compare that 3rd one with a VN1600:

Takes a bit of audio discernment, but I hear a similar sound pulse from the dual carbbed XR1000 and the VN1600. Also, doesn't matter that I used a Sportster to compare with the 1600. The larger Harleys and the Sportster both have 45 degree v-twin engines and single air intake systems. There are some twin carb conversions for Shovelheads, but no sound tracks that I've found.

[ponch]

I think Twin cam and later use single fire as do later sportsters.

[OldSchool]

Originally Posted by hayes

The original hd was made from a 10 cylinder plane engine. You get that sound because the crank is still based of ten cylinders. You get fire on 1 then 2 but then you have 8 missing fires. That's the "hesitation" you're hearing.

I was told that by a Harley historian and it made sense. I have no idea if it's true, but I believe it...

V Twins were around way before airplanes ever flew.

http://en.wikipedia.org/wiki/V-twin_engine

[Sparks500]

I'm no mechanic, but, a few years back I read an article about this same thing. They did mention the simultaneous firing plugs and the fact that most, if not all, metric v-twins have 4 valves per cylinder compared to Harley's 2.
Harley's do have a nice sound, I'm just leery of an engine without an oil sump.

[macmac]

Originally Posted by Sparks500

I'm no mechanic, but, a few years back I read an article about this same thing. They did mention the simultaneous firing plugs and the fact that most, if not all, metric v-twins have 4 valves per cylinder compared to Harley's 2.
Harley's do have a nice sound, I'm just leery of an engine without an oil sump.

Dry sump works upside down, and so is no problem at all. This may have come to be in WW-1 for air planes but I don't know that is the reason. Porsche 911's had that system and maybe still do.

[ubernomad]

Originally Posted by Sparks500

I'm no mechanic, but, a few years back I read an article about this same thing. They did mention the simultaneous firing plugs and the fact that most, if not all, metric v-twins have 4 valves per cylinder compared to Harley's 2.
Harley's do have a nice sound, I'm just leery of an engine without an oil sump.

The newer 2014 model year Twin Cam 103 motor in my father's Dyna LR is not a wasted spark design....it has dual (2) coils for true 1-2 firing just like the Vulcan engine. One coil for front cylinder and one for the rear cylinder. But it still sounds like a Harley should, which leads me to believe the ignition system (aka wasted spark) does not contribute to the HD sound. According to what I've read HD has moved away from the wasted spark design due mostly to emissions control and the fact that modern day electronic ignition systems are pretty darn reliable. The only reason they used the wasted spark design was to simply production, reduce cost, and provide a more "reliable" ignition system by having only one coil and no distributor.