Toyota 20R engines: details and photos
Introduced in 1975 in the Celica, Corona, and Half-ton Pickup, the 20R engine used a semi-hemispherical head design for optimal fuel-burning and power generation at high rpm; it was however designed to meet and beat emissions standards as well, without the power-sapping add-ons other manufacturers were resorting to. The 20R was a 2.2 liter (2189cc) single-overhead cam (SOHC) design, using an aluminum alloy cylinder head with cross-flow design to reduce premature fuel vaporization (surging) and percolation (flooding) in hot weather.
Externally, the 20R featured both an electric fuel pump (still unusual at the time) for steady fuel delivery and to avoid vapor lock, coupled with a better fuel return system that smoothed idling by keeping a constant supply of fuel at a more even pressure and temperature. The two-barrel downdraft carburetor featured a coolant-driven automatic choke, for more even operation.
The 20R also used electronic ignition, whose worldwide first use was in 1971 (by Chrysler Corporation); by no means was this system commonplace. The 20R was used with a larger, more efficient three-row radiator core and seven-blade viscous-driven fan to prevent overheating.
The 20R engine was a single-overhead-cam design, chain-driven, with eight valves (two per cylinder).
* USA numbers. 1975 introduction: 96 horsepower @ 4,800 rpm except California, 90 hp @ 4,800 rpm in California. By 1979-80 this had changed to 90 hp @ 4,800 for all 50 states.
Because of its new design with emissions in mind, the 20R engines required “less tubing and plumbing” and fewer moving parts, yet emissions were well within regulations when introduced in 1975. Part of the improvement was in the air injection system itself, which was still used. A catalytic converter was used on Corona and Celica in the United States, but not the half-ton, which could use either regular or low-lead gas; the cars, due to the converter, had to use unleaded (but regular unleaded).
Toyota claimed more usable power than with the 18R, because maximum torque was achieved at about 55 mph in fourth gear (which was a function of both engine and gearing); and claimed that the 20R was simpler, more durable, and easier to maintain than the 18R.
The 20R was coupled to a five-speed or four-speed synchromesh manual transmission, depending on model, or (again, depending on model) a three-speed automatic. The clutch diameter was 8.8 inches regardless (only Corolla and Land Cruiser got different clutch sizes in 1975; neither used the 20R). Gear ratios, as of 1975, were: