Ima,

The T34 IS a T3 derivative!!!! The exhaust wheel is identical to the std turbo and hence why when fitted with a 0.48 exhaust housing a T34 is very similar to the std turbo. The only difference a T34 has is a slightly larger compressor wheel and the larger A/R 60 compressor housing. This essentially makes the T34 60bhp potential up on standard.

I.E a std turbo will sit at 300bhp as its reliable limit where as a T34 is at 360bhp. (320bhp for the 60 trim 4X4 T3)

Even with a 0.63 exhaust housing the exhaust wheel is just as restrictive and why a T34 is not even in the same ball park as the T4.

Don't get me wrong I like the T34, its a fantastic little turbo, but they simply don't have the flow potential to give you increasing power all the way to the limiter like a T4!