Sorry about the double-posts ... but I would highly reccomend a larger exhaust housing if you're going to do an exhaust for your car. On the 05cm^2 housing a couple quick calculations (did them just now) will show that gas speed is well over the local speed of sound at 5,000 RPM. Once the gas reaches the sound barrier it is governed by normal and oblique shock relationships and is now a compressible fluid.

Once the gas through the turbine reaches the local speed of sound the only way to increase the mass-flow through the orifice is to increase the

**absolute pressure** or the size of the orifice and pressure-ratio no longer has any significant effect. This means the backpressure from your

**post-turbo** exhaust system will have neglidgable effect beyond 5,000 RPM because pressure ratio no longer dictates flow, only absolute pressure.

Mean Piston Velocity @ 5,000 RPM: 2.0L 13 m/s ----- 2.3L 15 m/s

Exhaust gas temperature: ~1073*K

Local Speed of Sound: 656 m/s (1,466 mph)

Gas Speed Assuming No Speed of Sound in the 05 cm housing @ 5K RPM: 2.0L 662 m/s ---- 2.3L 765 m/s

If you look at the turbine maps at ATP Turbo you can see the choke flow; it's when the corrected exhaust gas flow no longer increases with pressure. (The mass-flow still goes up, but not the velocity.)

The same calculations for an 06 cm housing, the exhaust temperature, and thus speed of sound, are assumed to stay the same:

Gas Speed Assuming No Speed of Sound in 06 cm housing @ 5K RPM: 2.0L 551 m/s --- 2.3L 636 m/s

You can see that with the larger 06 cm housing neither the 2.0 nor 2.3L reach choke flow before 5K rpm. After getting the larger housing, a better flowing POST-TURBO exhaust will make a significant difference in top-end flow ... and power too if you get a good tune.

Adrian~