Jay Honeck wrote:
I think he might have meant that a direct
drive unmuffled flat-four sounds rough
at idle compared to most cars. And I'd
agree.

It's that "unmuffled" (or partially muffled, at best) part that gives
it that characteristic quality.

Our friend has an airplane powered by an unmuffled Chevy V-8, and it
sounds just as sputtery at idle...


Funny cars and TF dragsters sputter. Most street cars don't even come
close! :-)

Matt