G25-550 has a 48mm compressor, G25-660 has a 54mm compressor. Both are capable of impressive numbers, especially for their size! THE BEST OPTIONS ON THE MARKET FOR A QUICK SPOOLING TWIN SETUP!!

G SERIES COMPRESSOR AERODYNAMICS FOR MAXIMUM HP
48/54mm TURBOCHARGER COMPRESSOR WHEEL
80% MAXIMUM COMPRESSOR EFFICIENCY
MAR-M ALLOY TURBINE WHEEL RATED UP TO 1050° C
NEW TURBINE AERO PROVIDES HIGHER FLOW AND EFFICIENCY
STAINLESS STEEL TURBINE HOUSINGS RATED UP TO 1050° C
OIL RESTRICTOR AND WATER FITTINGS INCLUDED
FULLY MACHINED SPEED SENSOR AND PRESSURE PORTS

Forged fully-machined compressor wheel and new aerodynamics increase maximum horsepower output and boost response. The CFD (computational fluid dynamics) engineered compressor wheel increases air flow up to 15% for 60mm and 30% for 67mm with 79-80% efficiency. (Compared to GTX Gen II)

A new one-piece center housing and backplate increase durability and product safety by reducing the number of failure points associated with the turbocharger. The center housing to turbine housing v-band connection allows for 360 degree orientation when installing with Garrett® non-wastegated turbine housings

Four large water jacket ports increase cooling capacity and allow enthusiasts to customize water line routing to help improve the installation process. The turbocharger comes with two -6AN water fittings and two plugs.

A single stage oil passage directs pressurized oil to the new oil cavity ensuring proper bearing lubrication at both sides of the cartridge.

Each turbocharger includes (1) -4AN oil restrictor fitting with a 1mm orifice to provide the turbo with the recommended 40psi of oil pressure.

A shorter bearing cartridge allows us to incorporate twin piston rings on both sides of the shaft wheel assembly. This will reduce the likeliness of oil leakage at the seals from the center housing to the compressor and or turbine stage.

The turbine wheel features all new aerodynamics to improve flow and boost response. The new turbine wheel is made of Mar-M super alloy and is capable of handling exhaust gas temperatures up to 1050 degrees C. The new turbine wheel flows 15-20% more than GTX and has peak efficiency of 74%.

All G Series Turbine housings are made from stainless steel to provide ultimate durability and temperature resistance up 1050 degrees C. Internally wastegated housings are compact, efficient, and designed with maximum bypass port size to reduce boost creep and provide better boost control.