Here's some measurements to help identify what dump pipe (O2 housing) you have. I found info hard to find so i took pics at times when Ive had them side by side.
A quick way to narrow it down on the car, drop the front pipe off and measure the outlet on the O2 housing/dump pipe, evo3 is 61mm ID.... vr4 and evo1-2 are 55mm ID.
Note the differences also between the inner and outlet lip on the joins with the O2 housing, and the exhaust housing.These are often easily ported, such as removing the flame ring between exhaust manifold and exhaust housing. And the exit from an O2 housing where the front pipe bolts up.
So the inner lip is what limits your flow, and can easily be ported out to the outer lip size, in both cases.
O2 housings/ Dump pipes
VR4:
Main entry behind exhaust wheel: 55mm
Outlet to front pipe (outer lip): 55mm
Outlet to front pipe (Inner lip) 50mm
Evo 1-2:
Main entry behind exhaust wheel: 63mm
Outlet to front pipe (outer lip): 55mm
Outlet to front pipe (Inner lip) 50mm
Evo 3:
Main enrty behind exhaust wheel: 63mm
Outlet to front pipe (outer lip): 61mm
Outlet to front pipe (Inner lip) 57mm
The exhaust housing outlet size matches the entry into the O2 housing. The evo 1-2 and evo 3 are the same size in to match the 070 housing.
The vr4 inlet is smaller to match the 060 housing outlet.
The differences i can see with the evo 3 dump. (See pics in post below.)
Its very close to 2.5 inch on the outlet.
The flange surrounding the outlet is larger allowing for more porting potential.
You can easily port the inner lip out to 2.5 inch. Or you can take it out further. 2.75 inch looks achievable, some get it close to 3 inch apparently. But you'd be getting close to the edge of the flange and need some material for the seal.
I also ported inside the inside of the bend behind the exhaust wheel, where it comes in around the bolt holes. To keep it as close to 2.5 inch internally. This along with the 2.5 inch outlet porting is the basic porting, then you can spend more time from there.
The merge of the wastegate passage is also smoother than the other 2.
While we are at it some exhaust housing measurements.
060
Entry from exhaust manifold, (Outer lip) where the flame ring sits inside: 54mm
Entry from exhaust manifold, (Inner lip) to match inside the flame ring: 46mm
Outlet behind exhaust wheel into o2 housing: 52mm
070
Entry from exhaust manifold, (Outer lip) where the flame ring sits inside: 60mm
Entry from exhaust manifold, (Inner lip) to match inside the flame ring: 53mm
Outlet behind exhaust wheel into o2 housing: 61mm
A quick way to narrow it down on the car, drop the front pipe off and measure the outlet on the O2 housing/dump pipe, evo3 is 61mm ID.... vr4 and evo1-2 are 55mm ID.
Note the differences also between the inner and outlet lip on the joins with the O2 housing, and the exhaust housing.These are often easily ported, such as removing the flame ring between exhaust manifold and exhaust housing. And the exit from an O2 housing where the front pipe bolts up.
So the inner lip is what limits your flow, and can easily be ported out to the outer lip size, in both cases.
O2 housings/ Dump pipes
VR4:
Main entry behind exhaust wheel: 55mm
Outlet to front pipe (outer lip): 55mm
Outlet to front pipe (Inner lip) 50mm
Evo 1-2:
Main entry behind exhaust wheel: 63mm
Outlet to front pipe (outer lip): 55mm
Outlet to front pipe (Inner lip) 50mm
Evo 3:
Main enrty behind exhaust wheel: 63mm
Outlet to front pipe (outer lip): 61mm
Outlet to front pipe (Inner lip) 57mm
The exhaust housing outlet size matches the entry into the O2 housing. The evo 1-2 and evo 3 are the same size in to match the 070 housing.
The vr4 inlet is smaller to match the 060 housing outlet.
The differences i can see with the evo 3 dump. (See pics in post below.)
Its very close to 2.5 inch on the outlet.
The flange surrounding the outlet is larger allowing for more porting potential.
You can easily port the inner lip out to 2.5 inch. Or you can take it out further. 2.75 inch looks achievable, some get it close to 3 inch apparently. But you'd be getting close to the edge of the flange and need some material for the seal.
I also ported inside the inside of the bend behind the exhaust wheel, where it comes in around the bolt holes. To keep it as close to 2.5 inch internally. This along with the 2.5 inch outlet porting is the basic porting, then you can spend more time from there.
The merge of the wastegate passage is also smoother than the other 2.
While we are at it some exhaust housing measurements.
060
Entry from exhaust manifold, (Outer lip) where the flame ring sits inside: 54mm
Entry from exhaust manifold, (Inner lip) to match inside the flame ring: 46mm
Outlet behind exhaust wheel into o2 housing: 52mm
070
Entry from exhaust manifold, (Outer lip) where the flame ring sits inside: 60mm
Entry from exhaust manifold, (Inner lip) to match inside the flame ring: 53mm
Outlet behind exhaust wheel into o2 housing: 61mm
