It’s natural for us competitive two-legged critters to want to present our favorite engines in the best possible light, but we do have to accept that it’s all relative.
After all, a Harley-Davidson or Indian Big Twin, making peak power at a low 5,500 rpm and peak torque of more than 100 pound-feet at an even lower 3,500 rpm, is a low torque, high-rpm engine when compared with Wärtsilä’s 100,000-hp marine application, delivering that power at 102 rpm—less than 1/50th of the Big Twin’s peak rpm—along with 5,000,000-plus pound-feet of torque, which is roughly 45,000 times greater than the peak torque of Big Twin motorcycle engines.
Wandering off the subject, you may object that the Wärtsilä marine engine is not in a bike, but who knows? Busy Australian enthusiasts are constantly building giant V-twin motorcycles around pairs of air-cooled cylinders from 1950s aircraft engines. What will they build next?
A cylinder sitting in my office is a case in point, taken from a 3,400-hp Wright 18-cylinder radial of 6-1/8-inch bore by 6-5/16-inch stroke. Two of those cylinders add up to a stout 372ci. Takeoff rpm for the original engine was 2,800, making today’s Big Twins, which rev twice as high, look like low-torque, high-rpm engines.
I decided to present torque in the form of pound-feet per cubic inch of displacement because it can be used to compare the torque-producing abilities of all engines.
Comparing specific torques measured in pound-feet per cubic inch of displacement, we find that Big Twins give just under 1.0, sportbike engines manage 1.25, our aircraft engine example gives about 1.9, and the marine engine about 1.87. A BMW Megatron 91.5ci inline-four of Formula 1’s 1980s turbo era, making 900 hp at 11,000 rpm for racing and maybe as much as 1,300 hp for qualifying, made peak torque around 600 pound-feet, for a specific torque of 6.5 pound-feet per cubic inch. That makes sportbike engines seem positively feeble. No doubt nitro-burning Top Fuelers make even more—10 or more pound-feet of torque per cubic inch—but they won’t get you to Sturgis because they have to be rebuilt every four seconds.
Once again, these engine types were designed to do very different jobs, so we soon find ourselves arguing nonsense questions like, “Is it hotter in the city or in the summer?” Let’s agree that we all enjoy motorcycling and get on with the different kinds of riding we enjoy.
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