CT20 Turbo Specificationsby Richard Rowe
Manufactured by Hitachi, the CT20 turbo has been used on a number of factory turbocharged engines, the most notable of which are the Toyota Supra, Celica and the mid-engined MR2. On the outer edge of its rpm range, this turbo is capable of supporting over 300 horsepower on single turbo cars and about 600 horsepower on the twin-turbo Supra.
Turbine Side Specs
The CT20's high nickel content turbine housing inlet's ID -- the inside diameter -- is 36 mm and the outlet ID is 50.1 mm. The ceramic turbine has 10 blades and rides on a 10-mm shaft. Its outlet diameter is 48 mm and its inlet diameter is 59.8 mm. The CT20 has a housing-to-turbine aspect ratio of 0.35. The turbine housing outlet on a standard CT20 is 47.8 mm, but the CT20A -- which is a secondary turbo used on Turbo Supras -- has an exhaust outlet diameter of 52.6 mm. The exhaust outlet's outside diameter is 56.3 mm for both, and both use a T4-style inlet flange.
The CT20's compressor housing's inlet ID is 49.8 mm and the outlet ID is 32.4 mm. The ten-bladed -- technically "twin five-blade" -- investment cast aluminum compressor wheel's inlet diameter is 37 mm and its outlet diameter is 62 mm. The compressor housing has an A/R of .36.
The turbo's bronze main bearing has six oiling holes per side and is 8.96 mm wide. The bearing's outside diameter is 15.9 mm and its inside diameter is 10.05 mm.
The standard CT20 uses a wastegate with a 26 mm ID, but it is capable of utilizing an aftermarket 28 mm wastegate. The stock actuator spring is preset at 10 pounds. To increase boost you'll need to either install a heavier-duty spring or utilize some sort of boost control. The rear CT20A turbo does not utilize a wastegate; rather, it uses an internal exhaust bypass valve to help ease the transition from the primary turbo.
The stock CT20 turbo is factory set for 10 psi of boost, but it is capable of producing more when used with electronic or manual boost control. The CT20 will produce as much as 18 psi, but you run the risk of turbo overspeeding if you push it that hard. The CT20 is good for about 14.7 psi of boost for approximately a 37 percent power increase over stock. If you want any more than that you should purchase a larger turbocharger.
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