Five Of The Lowest-Revving Production Gasoline Engines Ever

Normally, we’re all about the highest revving, highest-performing engines here at EngineLabs. However, sometimes, the technical marvel isn’t in spinning it to the moon, but rather making solid power down low. Normally, the low-RPM range is the playground of non-gasoline engines, whether spark-ignition like liquid natural gas engines or compression-ignition engines like diesels, so doing it with traditional gasoline is a bit of a unique feat.

While the video in the article features a lot of different engine types, we’re going to pare that list down, and only focus on a select few engines. Make sure to watch the video all the way through to see all of the low-RPM marvels of mechanical engineering on the list. If you just want our take on five of the more interesting engines, read on.

Hudson H-145 Straight-Six

Debuting in the late 1940s and then “refreshed” in the early ‘50s for use in the Hornet, the Hudson H-145 engine was a “high-compression” engine in those days, with a stout 7.2:1 compression ratio. The large undersquare configuration of a 3.8125-inch bore and 4.500-inch stroke made it the largest six-cylinder production engine of the day at 308 cubes, but gave it a very low power peak, with the more performance-oriented “Twin H-Power” model producing 160 horsepower at 3,800 rpm and 260 lb-ft at 1,800 rpm

The H-145 also enjoyed factory performance support and saw dominant use in the NASCAR circuit in the early ‘50s, especially when tuners and engine builders jumped into the fray. This gave the H-145 the distinction of the first factory-backed NASCAR engine program. Its run in the Hornet lasted until the 1957 model-year, when the Packard V8 offered more power at a lower price point.

The H-145 engine’s upgraded factory variant was the “Twin H-Power, which used two single-barrel carburetors and made a peak of 160 horsepower at 3,800 rpm.

GMC Twin-Six 702 V12

Eagle-eyed readers might recognize this one from an article we published back in 2013. The GMC Twin-Six is a V12 engine that displaces a whopping 702 cubic inches. At first glance, it looks like two V6 engines welded together (probably due to the two intake manifolds, two distributors, three-cylinder valve covers, and exhaust manifolds used. Make no mistake, this is a single massive block, and a single-piece, forged-steel, 180-pound crankshaft (even though there are more than 50 interchangeable V6 parts used.)

Its main marketing message was that it could go 200,000 miles with proper maintenance before needing a major overhaul. Surprisingly for a low-RPM engine, the bore and stroke were oversquare, with a 4.560-inch bore and 3.580-inch stroke totaling up to 702 cubic inches. In its heyday, the 702 was rated at 275 horsepower at 2,400 rpm and 630 lb-ft of torque at only 1,600 rpm. Stout for a naturally aspirated gasoline engine, even by today’s standards.

The "Twin-Six" 702 cubic-inch V12 engine uses quite a few parts from GMC's "big-block V6" engine platform, but wasn't just two V6 engines combined. The one-piece block and forged 180-pound crank are their own parts.

Daimler-Benz 601 “Inverted” V12

If you follow our Facebook page at all, you know this engine has come up several times in the past few weeks. Known as the upside-down V12, the DB 601 was built to operate with the cylinder heads on the bottom and the oil pan up top in order to increase the field of vision for the pilots of the Messerschmitt Bf-109. Aviation engines don’t typically operate at high-RPM, so this really isn’t a shocker, but the amount of power made and such low engine speeds, is impressive.

The engine was undersquare, with a 5.906-inch (150mm) bore and a 6.299-inch (160mm) stroke for a total displacement of 2070 cubic inches, or 33.9 liters. It featured mechanical fuel injection and a dry-sump oiling system (obviously), along with a gear-driven centrifugal supercharger (which was later driven hydraulically). The DB 601 had a number of variants with the most powerful version creating 1,430 horsepower at only 2,700 rpm.

These Daimler Benz engines from the Me-109 WWII fighter were built inverted in order to increase the pilots’ visibility.

Ford N-Series Four-Cylinder Flathead

Used in the early 1930s in the N-series of tractors, the four-cylinder flatheads weren’t particularly powerful, only making between 23 and 28 horsepower throughout the range of variants, at an astonishingly low 2,000 rpm. However, the most interesting part of the N-series lineup, is that it used many of the same parts as the legendary Ford Flathead V8, with some hot-rodders even heading to the local Tractor Supply store to get two piston kits for their V8.

While you might be scratching your head at this one, these engines and the tractors they powered still enjoy a healthy enthusiast following today. While they might not be a low-RPM powerhouse, they are still an interesting low-RPM engine, nonetheless.

Aultman and Taylor 30-60

Another tractor engine, this one only made the list because of its incredibly low RPM limit — certainly not the 80 horsepower from its 1385.4 cubic inches of displacement. Granted, we’ll cut it some slack since the design is over 100 years old, but still, the fact that its redline is lower than most modern four-cylinder engines’ idle is impressive.

The hugely undersquare engine design features a 7.00-inch bore with a 9.00-inch stroke and creates a dismal HP/CI ratio of about 0.058 horsepower per cubic inch at its peak of 550 rpm (no, we didn’t leave out any digits) — a far cry from some of the other low-RPM engines on this list. In addition to its massive displacement, it also holds a massive amount of coolant: 120 gallons worth. Were not really sure what is generating all that heat, because it certainly isn’t from making big power.

The N-series Ford engines were based on the famous Flathead V8 architecture, with many interchangeable parts.

About the author

Greg Acosta

Greg has spent fifteen years and counting in automotive publishing, with most of his work having a very technical focus. Always interested in how things work, he enjoys sharing his passion for automotive technology with the reader.
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