Morning chaps, sorry for the delay, ive been on holiday.

The T38 uses a ported rear end normally so does increase the engine's VE quite a lot which is where a lot of teh gains come from, but also remember this:

A T34 flat out with greys wil normally have a closed or almost closed wastegate at high rpm due to teh fact the engine is consuming more air than it can supply so we are running the compressor at max speed and usually well off its efficiency island.

A T38 will have an open wastegate at this point and as a result will increase the engines VE due to reduced T.I.P and teh fact the compressor is actualy still within a decent efficiency range. Allied to this larger compressor having a greater adiabatic efficiency and producing somewhat cooler air than the T34 did, you are looking at a serious leaning of the fuel mixture at high rpm on a t34 map.

One question always worth asking yourself:

"If it DOESNT make my engine run leaner, should i actually bother fitting it at all?"

Think about that one carefully...