Fast Talk With Jeff Smith: Big Engines – Really Big Engines

I found a data plate the other day in my tool box that had been covered up for at least a few years. It’s a little bit different than your normal VIN plate or option code plate found on the firewall of a Camaro. This one came off the engine of a Pratt & Whitney Aircraft engine. Specifically, a R-2800 Double Wasp WWII aircraft engine. The 2800 designation stands for the engine displacement – in cubic inches. We’re talking a beast of a radial with two rows of 9 cylinders. The WWII-era photo gives you a clue about how big this rascal is – the specs I found online report that depending upon its configuration, the engine could weigh anywhere from 2,150 to 2,550 pounds!

These engines were used in several famous WWII planes including the F-4U Corsair, the B-26 light bomber, the F6F fighter and even the P-47 Thunderbolt, affectionately called the Jug. The engine has a 5-inch bore and a 6-inch stroke (that computes to 2,804ci with 18 cylinders). The plate lists the compression ratio at 6.65:1 because these engines all used a centrifugal supercharger to boost power since these planes typically flew at altitudes of 30,000 feet and higher  – the P-47’s rated ceiling was 43,000 feet!

Other plate goodies include maximum ignition timing of 20 degrees BTDC. A couple of the more interesting specs are Valve Timing Clearance numbers. For the intake, the spec is 0.143-inch at 76 degrees ABDC for Intake Closing and the same spec and degree figure for exhaust opening BBDC. I’m going to assume this clearance is the valve-to-piston clearance so the mechanic would crank the engine over until the intake valve was at 76 degrees after bottom dead center and then measure the valve to piston clearance. This is not the actual cold valve lash clearance – that spec is also stamped in the plate telling you to look it up in the manual. I found that spec at 0.060-inch! Remember, this is an all-aluminum radial engine that is downright huge. That means the engine probably grows by at least 0.040-inch – perhaps more.

While poking around the internet, I found a maintenance manual that listed the required oil as 100 viscosity rated at 210 degrees F. Remember, this was the 1940’s when oil wasn’t nearly as good as it is today. That led me to find a recommendation for cold weather operation where the mechanics were required to mix high-octane gasoline with the oil as a percentage based on the ambient temperature. This was done to essentially reduce the viscosity of the oil. Think about that – SAE 100 oil at 30 degrees F would literally be a solid chunk. So they’d have to reduce the viscosity by mixing gasoline with it. That’s probably why you see vintage footage of these radial engines starting with a man standing next to the engine with a giant fire extinguisher. If that engine back-fired for any reason, that could get ugly pretty quickly!

This particular R2800 is a model 75 which I found listed as making 2,200 horsepower. I found specs on a different version 2800 engine with the peak horsepower rated at 2,400 rpm. I used the classic horsepower equation to work backward to get the torque. At 2,400 rpm at 2,000 horsepower, the engine is also making a mind-numbing 4,376 lb-ft of torque. That will move some air!

 

My buddy Tim Moore’s shop was located behind a company called Aircraft Cylinder that used to rebuild these engines until the company reorganized a few years ago. While they were moving out of their building, we found this data plate on the ground. Ironically, at the bottom of the plate, you can see that this engine was built by the Ford Motor Company. So there’s our tie-in to cars – as if we needed one!

About the author

Jeff Smith

Jeff Smith, a 35-year veteran of automotive journalism, comes to Power Automedia after serving as the senior technical editor at Car Craft magazine. An Iowa native, Smith served a variety of roles at Car Craft before moving to the senior editor role at Hot Rod and Chevy High Performance, and ultimately returning to Car Craft. An accomplished engine builder and technical expert, he will focus on the tech-heavy content that is the foundation of EngineLabs.
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