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 inside diameter (ID) is 36mm and the outlet ID is 50.1mm. The ceramic turbine has 10 blades and rides on a 10-mm shaft. Its outlet diameter is 48mm and its inlet diameter is 59.8mm. The CT20 has a housing-to-turbine aspect ratio (A/R) of 0.35. The turbine housing outlet on a standard CT20 is 47.8mm, but the CT20A (which is a secondary turbo used on Turbo Supras) has an exhaust outlet diameter of 52.6mm. The exhaust outlet's outside diameter (OD) is 56.3mm for both, and both use a T4-style inlet flange.
The CT20's compressor housing's inlet ID is 49.8mm and the outlet ID is 32.4mm. The ten-bladed (technically "twin five-blade") investment cast aluminium compressor wheel's inlet diameter is 37mm and its outlet diameter is 62mm. The compressor housing has an A/R of .36.
The turbo's bronze main bearing has six oiling holes per side and is 8.96mm wide. The bearing's outside diameter (OD) is 15.9mm and its inside diameter is 10.05mm.
The standard CT20 uses a wastegate with a 26mm ID, but it is capable of utilising an aftermarket 28mm wastegate. The stock actuator spring is preset at 4.54kg. To increase boost you'll need to either install a heavier-duty spring or utilise some sort of boost control. The rear CT20A turbo does not utilise 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 per cent power increase over stock. If you want any more than that you should purchase a larger turbocharger.