Engine Sounds by type

Do all V twin motorcycle engines go 'potato-potato-potato'? Maybe the 'envelope' of the 'bangs per sec' is similar for each type?

It has to do with firing order, and the logical combining of exhaust pipes. A straight six with split manifolds 3/3 like a BMW makes for a smooth yet sweet sound. The V-8 "lope" is because the firing order is generally 1-8-4-3-6-5-7-2 yet the exhaust pipes are combined 1-3-5-7 and

2-4-6-8, so you have the 8-4 and 5-7 pulses right next to each other in the same pipe, with the delay between 1-3 and 6-2 being longer, so each pipe gets pulse-wait-wait-pulse-wait-pulse-pulse-wait, 180 degrees out of phase with each other (well, that's 180 degrees of *cam* but 360 degrees of *crank...* you get the idea, anyway) if a V-8 is set up with an even fire exhaust like some old mid-engine racers (GT40 comes to mind) it sounds a lot like a straight six, but more so, but the exhaust looks like a bundle of drunken snakes. A V-12 is basically like two straight sixes put together, so they sound really smooth as well.

V6's sound like shit because there's no natural way to even out a V6 and also have it balanced. Four cylinders sound like I-6's but a little rougher, which you'd expect. Boxers sound unique, and to be honest I'm not sure why, maybe it has something to do with the necessity to have the two main exhaust pipes separated for a while before they come together (if they ever do.)

Then there's esoterica like how V-8s with siamesed center exhaust ports, like old flathead Fords, Studebakers, and early Caddys might not be as efficient as a modern head/exhaust design but they sound oh so good... something about combining the 3/5 and 2/4 ports makes the exhaust get all nasty sounding...

nate

Only odd-fire ones like a Harley. I believe they actually have registered their exhaust sound as a trademark, although I don't know if that's ever been challenged. I don't know that anyone else would want to copy Harley's crank/vee layout; it works, but it's not the smoothest-running cat skinner.

nate

I'm pretty sure that they did, and it has, and the "Vulcan" engine had to be changed so that it didn't sound like a Harley because of it.

Huh. I like the sound of a V6, especially the old Buick (1960s type).

It's the boxer's firing order again. On an opposed four, the left two cylinders fire, then the right two, and since the cylinders on each side are usually plumbed together exhaust-wise, they have this (left)pop-pop(right)pop-pop sound to them. Some of them, notably in some aircraft such as the Piper Cherokee, have the exhaust plumbed so that they fire evenly; it takes a bunch more pipe and with the different lengths they end up sounding about the same anyway. Opposed sixes have a totally different firing order so thay have a unique sound of their own. There's an opposed eight, but I've never heard it. Not very common. It's the Lycoming IO-720, seen here:

The chrome pipes are intake runners, not exhaust pipes. Noexhaust in installed in this picture. I miss my old 13-foot Cracker Box-style boat with its completely-hidden Chev 283. Shoulda seen the looks on people's faces when that tiny boat fired up. I don't think I could build another one now, with all the new rules about how much power you can put in a given size of boat. Either that, or that V-8 would have to be "derated" to 50 HP or so...

Dan

Firing order as determined by crankshaft and camshaft geometry, and placement of the exhaust ports and the related exhaust plumbing. The V8, in particular, has its trademark sound because when you build it with a 90-degree crank (as 99% of street cars are because of balance) it causes a pair of cylinders on each bank to fire in sequence. IOW, if "L" represents a cylinder firing on the driver's side (left) bank and "R" represents a cylinder firing on the passenger's side (right) bank, then a 90-degree v8 firing order is L-R-L-L-R-L-R-R-L-R-L-L.... etc. The paired firings on alternate banks cause the "v8 burble" even if the pipes get plumbed into a single exhaust eventually. There are several possible physical firing orders for a v8 (for example, aftermarket cam companies often swap 2 cylinders on the small-block Chevy for better performance) but ALL the valid firing orders still have that pairing on each bank at some point during the order. V6 engines don't do that- they strictly alternate banks like a pair of 3-cylinder engines running slightly out of phase.

FWIW, a "flat crank" v8 does NOT make that sound. But as I said, most poeple never hear a flat-crank v8 because they're so rare. IIRC, the Indy Racing League used (or still uses) flat-crank v8s. I know they did when Oldsmobile and Infiniti were supplying the engines years back, anyway.

They filed for it in 1994 and gave it up after six years of contention against other motorcycle manufacturers. I'm not sure whether this resulted in any great landmark at the legal frontier of copyrighting of sounds, or just affirmed the well-known principle that a law fight can be dragged out for a long expensive time.

A friend once pointed out something that should've been obvious, but which I overlooked for many years: it's a special and simplified case of the engine layout known as a "radial," once commonly used for aircraft. Anyway, there are several vee-twin motorcyle engines (common crankpin or otherwise). It's one of the oldest arrangements and (thin ice ahead) may have seemed to early designers like the most logical way to build two cylinder engines after usually starting out with one cylinder. Indian and Marsh-Metz come to mind as companies that had V-twins (of one angle or another) even a few years before Harley and Davidson came out with theirs. It was an idea much in the air in the early 1900s, I guess, or at least the logical next step.

Some cool stuff:

Thanks to everyone for the replies. It's been an informative and entertaining read!

"bundle of drunken snakes" is my new favourite term.

-ph

That's not really true. a 60-degree v6 alternates banks, fires even, and is (reasonably, about like a v8) well-balanced.

and it's reasonably accurate as well :)

nate

Good point; I was thinking about 90 degree sixes.

However, the engine in my Impala still sounds like shit, while the I-6 in my old BMW 535i had a wonderful ripping-cloth exhaust note that was practically guaranteed to put a little woodrow in your wilson. Not sure why that is.

nate

A former contributor here (you should know who) has said for years that a slant-6 through Dutra Duals (front/rear split) sounds lovely, while a v6 through duals sounds like shit. I politely nod, but to me they *both* sound like equal shit (or at least wet farts). But I agree that an inline 6 through a *single* exhaust sounds altogether different, and for some reason plumbing a v6 into a single exhaust won't make it sound as silky an inline 6.

I imagine, although haven't had the pleasure, that a 225 with the exhaust you describe would sound an awful lot like my old Bimmer, at least until it ran out of revs. I would ASSume with a little howl added from the 4-bbl. carb (why bother with dual exhaust if you don't Hyper-Pak it as well?) Having owned both, the engines even LOOK very similar, with the main difference being that the Bimmer's exhaust is on the passenger side (crossflow head) and the Bimmer has an overhead cam.

The one V-6 that I have heard that sounds fairly sweet is the current VW/Audi V-6, its exhaust sounds quite similar to the earlier VR6 which I'm not considering to be a true V-6 for purposes of this discussion as it had a 15 degree bank angle and a single head; for all intents and purposes it was essentially a really cleverly packaged inline motor.

Your post reminds me, I have some 70's vintage Cibies that I was going to put in my '55...

nate