Turbo Terminology
http://forums.nicoclub.com/zerothread/290341

Aspect Ratio or Area / Radius: It is the area of the housing divided by the radius of the housing.

Wastegate: A wastegate is a valve that diverts exhaust gases away from the turbine wheel in a turbocharged engine system. Diversion of exhaust gases causes the turbine to lose speed, which in turn reduces the rotating speed of the compressor. The primary function of the wastegate is to stabilize boost pressure in turbocharger systems, to protect the engine and the turbocharger. The wastegate is controlled by a wastegate actuator in which the actuator is controlled by pressure coming from the intake manifold.

Internal Wastegate: An internal wastegate is an integral part of the turbine housing. The wastegate actuator is commonly attached to the compressor housing with a metal bracket. A flapper valve is generally used by internal wastegates. A boost controller is needed to control boost.

External Wastegate: An external wastegate is a separate self-contained mechanism typically used with turbochargers that do not have internal wastegates. An external wastegate requires a specially constructed turbo manifold with a dedicated runner going to the wastegate. The external wastegate may be part of the exhaust housing itself. External wastegates are commonly used for regulating boost levels more precisely than internal wastegates in high power applications, where high boost levels can be achieved. External wastegates can be much larger since there is no constraint of integrating the valve or spring into the turbocharger and turbine housing. It is possible to use an external wastegate with an internally gated turbocharger, though this generally involves welding the internal wastegate shut to avoid unwanted leaks.
External wastegates generally use a valve similar to the poppet valve found in the cylinder head. However they are controlled by pneumatics rather than a camshaft and open in the opposite direction. External wastegates can also use a butterfly valve, though that is far more rare.

Divorced/Atmospheric wastegate: A “divorced” wastegate dumps the gases directly into the atmosphere, instead of returning them with the rest of an engine’s exhaust. This is done to prevent turbulence to the exhaust flow and reduce total back pressure in the exhaust system. Divorced wastegate dumper pipes are commonly referred to as “screamer pipes” due to the unmuffled waste exhaust gasses and the associated loud noises they produce.
Internal gates cannot generally be vented to the atmosphere because the internal wastegate port and turbine exducer are built into the same housing. Occasionally an exhaust downpipe for an internally gated turbocharger will be called ‘divorced’ because it integrates two tubes where one is intended for the wastegate only. It should be noted that it is difficult to truly separate the exhaust flow of the turbine and wastegate. Thus, internal wastegate turbos will rarely if ever feature an external dump.

Boost Controller: Boost control is the principle of controlling the boost level produced in the intake manifold of a turbocharged or supercharged engine by affecting the air pressure delivered to the pneumatic and mechanical wastegate actuator. Boost controllers can be as simple as a manual boost controller which can be easily fabricated oneself. One may also be included as part of the engine management computer in a factory turbocharged car, or an aftermarket electronic boost controller such as those made by Apex-i or GReddy.

Manual Boost Controller: A manual boost controller is a simple mechanical and pneumatic control to allow some pressure from the wastegate actuator to escape or bleed out to the atmosphere or back into the intake system. This can be as simple as a T-fitting on the boost control line near the actuator with a small bleeder screw. The screw can be turned out to varying degrees to allow air to bleed out of the system, relieving pressure on the wastegate actuator, thus increasing boost levels. These devices are popular due to their negligible cost compared to other devices that may offer the same power increase.

Electronic Boost Controller: Electronic boost control adds an air control solenoid and/or a stepper motor controlled by an electronic control unit. The same general principle of a manual controller is present, which is to control the air pressure presented to the wastegate actuator. Further control and intelligent algorithms can be introduced, refining and increasing control over actual boost pressure delivered to the engine.

Blow Off Valve: A blowoff valve is a pressure release system present in turbocharged engines, its purpose is to prevent compressor surge and reduce wear on the engine.

SR20DE/T Engine Specifications

JDM Pulsar GTI-R: Manufactured between 1990-1994 with a 226 bhp rating @ 6400rpm, producing 209 lbs/ft @ 4000rpm.
Top Mount Inter-cooled / 444cc injectors / quad throttle bodies / T28 Turbo (part # 14411-54C00) / Engine compression ration : 8:3:1.

JDM Bluebird (U12): Manufactured between 1989-1991 with a 202bhp rating @ 6000rpm producing 201 lbs/ft @ 4000rpm.
Top Mount Inter-cooled / 370cc injectors / T25 Turbo part # (14411-79E00) / Engine compression 8:5:1.

JDM Bluebird (U13): Manufactured between 1991-1996 with a 206bhp @ 6000rpm, producing 201 lbs/ft @ 4000rpm.
Front Mount Inter-cooled / 370cc injectors / T25 Turbo part # (14411-1E000/79E00) / Engine compression 8:5:1.

JDM Avenir (W10): Manufacture between 1995-1998 with 226bhp @ 6000rpm, producing 203 lbs/ft @ 3600rpm.
Front Mount Inter-cooled / 370cc injectors / T25 Turbo part # (14411-1E000) Engine compression 8:5:1.

JDM Avenir (W11): Manufactured between 1998-2002 with a 226bhp @ 6000rpm, producing 203 lbs/ft @ 3600rpm.
Front Mount Inter-cooled / 370cc injectors / ball bearing T25 Turbo part # (14411-WA200/WF500) Engine compression 8:5:1.

USDM SR20DE: Engines manufactured between 1991-1999 with a 140bhp @ 6400rpm, producing 132lbs/ft @ 4800rpm. Engines manufactured between 2000-2001 had a 145bhp @ 6400rpm, producing 136 lbs/ft @ 4800rpm.
Natural Aspirated motor with 9:5:1 compression / 259cc injectors.

JDM SR20DE: Manufactured between 1992-1998 with 150bhp.
Natural Aspirated motor with 10:1 compression / 259cc injectors
*ONE INDICATOR OF THIS MOTOR ARE FLAT TOP PISTONS*

References:

http://en.wikipedia.org/wiki/Nissan_SR_engine
http://en.wikipedia.org/wiki/Wastegate