R975 Radial engines

[Hanno Spoelstra]

Originally Posted by Bob Phillips

Continental manufactured the R975 under licence from Wright and made many thousands of engines- far more than were ever made as aircraft engnes. The earliest tank versions were called R975-EC3 I believe, and rumour has it they used high octane (100) aviation gas - but none of my manuals confirm this. Hanno do you know?

Bob,

Thanks for posting this interesting info. I love the sound of radial engines! As you say they are not particularly well suited for use in tanks, but at the time aircraft engines were the only engines with the power output needed to propel AFVs.

Early M3 Medium tanks and Ram Cruiser tanks were fitted with the Continental R975-EC2, a licence produced Wright Whirlwind. My copy of Data Book: Tank Type Vehicles of Canadian Manufacture dated January 1944, states: "The R975-EC2 Series Engine requires 91 Octane Aviation fuel, while the R975-C1 operates on 80 octane motor fuel (the standard fuel used by the mechanized forces of the United States Army). This is accomplished by changing the compression ratio of 6.3:1 in the R975-EC2 to 5.7:1 in the R975-C1, by a design change in pistons and changes in spark advance and in the carburetor main metering jet."
It lists for the R975-EC2:
- rated horsepower: 400 at 2400 rpm
- torque: max. 890 ft.lbs. at 1800 rpm
The Data Book refers to: Hand Book Continental R975-EC2 Ordnance Engine. Continental Motors Corporation, Detroit, Mich., April 1941.

Regards,
Hanno