Machine Design, Editorial Comment
July 6, 2000

What have you done? You have just vocalized the sound of an automotive V8 engine. Now try this one: Potato, potato, potato. That is the sound of a Harley-Davidson motorcycle at idle. How about this? Dewgee, dewgee, dewgee. That, of course, is a radial aircraft engine at idle.

By now you are wondering what this is all about. Well, back in our May 4 issue, this column talked about the euphonious sound made by the exhaust of automotive V8 engines. I went on to say that I could not figure out what gave the V8 its distinctive sound, which is so much more mellifluous than that of other types of powerplants. So far, more than 30 readers have written to us about the column. Some expressed the same puzzlement I had, but many of them had explanations for the V8's distinctive signature. The consensus is that the V8's sweet sound comes from two cylinders in each bank of the engine firing in succession, separated by firings in alternating banks.

So you have the following pattern from left bank to right bank: Left, left, right, left, right, right, left, right. If each bank gives a slightly different tone, you get the pattern of dewgs and deegs described in the first paragraph. One reader says the effect is similar to tones coming from two organ pipes. Thus, the V8 plays a chord rather than just a single note, with a chord being a much more pleasant sound.

Several readers suggested that the Merlin and Allison V12 aircraft engines sound even better than V8s, but I disagree. From time to time I have been able to get ramp privileges at air shows featuring warbirds, and until I amassed more than two hours of video, my hobby was taping engine starts while standing near the airplane. The sweetest sounds come from the radials, especially the 18-cylinder double-row engines.

With regard to the V12s, the first time I stood close to a Merlin at start up, it was in a Spitfire, and I was barely off the wing tip beside the engine. The prop began to turn, the engine came to life, and . . . fttt, fttt, fttt . . . the Merlin sounded like a Volkswagen Beetle.

What a disappointment! Where is the sound? Was the tone unimpressive because I was standing beside the airplane hearing just one bank of six cylinders, with the noise of the other bank blown away by the propwash? Would the Merlin have sounded better if I had been behind the tail where I could hear both banks? I don't think that was it. Even the legendary Mustangs, also Merlin powered, don't sound particularly awesome as they taxi by.

Incidentally, I have video of an S-51D Mustang, a 3/4-scale kit plane powered by a Chevrolet V8, and it is something to behold as it makes a low-pass over the runway. You see a Mustang roar by with the exhaust sound of an unmuffled 454 Chevy. It looks and sounds weird, like Top Gun running in Nascar.

Back to Harley-Davidson, a few years ago, the company filed for a trademark so it could have exclusive rights to the sound made by its 45° two-cylinder engine. I don't know how that came out. But what I do know is that when I hear potato, potato, potato, I know what brand of bike I'm listening to.

-- Ronald Khol, Editor