Turbo
From Celica GT-Four / Alltrac - ST165 ST185 and ST205
Available Unit IDs: C01, C02, C03, C04, C05, C06, C07, S01, S02, V01, V02, V03.
Example: <google uid="C01"></google>, <google uid="C01" position="left" ></google>
3 Types
AFAIK there are 3 main types of turbo on the Celica GT4, two CT26's and a CT20b. The CT26s original version on the ST165 was a single entry item I think - correct me if you know more on the 165. The 185s had twin-scroll CT26s which came with ceramic exhaust turbines if they were JDM cars. ST205s have the "CT20b" - a better turbo (though not as hybridisable) than the CT26 - flows more efficiently at higher speeds, it has a larger compressor and slightly larger inducer internal diameter, though the pipework is the same. Also came in steel and ceramic turbo I'm told.
The CT26 in standard form is considerd good for ~14psi, the CT20b for ~16psi. They can be pushed further but are then outside their efficiency envelope and tend to produce a lot of heat.
The CT20b can be swapped onto a 185 without much problem, you will have to rig up another turbo support bracket and may have to tweak the routing of the oil drain hose, and re-drill the heat shield, but it will go on with minimal effort and makes a nice and noticable upgrade - only worth doing if your CT26 is dying though.
Twin-scroll or Twin-Entry
When all 4 exhaust ports exit into one chamber of a single entry turbo they interfere with each other. The pulses of exhaust gas counteract each other to some extent, making the turbo less efficient. The twin-entry turbo feeds pairs of ports into their own "side" of the turbine to reduce this interference and make the turbo more efficient and spool earlier.
Toyota CT26/CT20 specs and diagrams
Images
