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It's a good approach you've got matching wheel diameters. A modern turbo is going to be more efficient and spool faster even if it's got similar size and geometry. This is mostly because blade shapes are better now.

But if you want to spool sooner/faster drop down turbine housing A/R size. That same SX200 should be available with a range of turbine housings.

I don't know how much boost those engines are good for.
 

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Comparing turbine size. The original turbine (63.5/73.5mm, 0.81 A/R) calculates out to a CCF (corrected choke flow) of ~28lb/min. This isn't a real flow number, it's intended to represent the flow size of the turbine.
Garrett get the same number with a 0.82A/R turbine in the maps above. Going smaller than that drives the turbo harder and generates boost faster.

Turbine trims grew to about 0.84 as understanding of the flows developed. Larger trims are more efficient and have a wider operating range Early turbines with smaller trim numbers choked out sooner and couldn't get as much energy from the expanding exhaust gas (because they didn't let it expand).

A good task next is to map out compressor air-flow and see what you need. Best plan is to map out max torque and max power points.
 
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