Need help understanding this guys. Someone told me it reduces backpressure plus more lag . What about top end TQ ect!!!!!

Before



After: One less blade

 

Looks like an evo 20g or 22g? Larger turbine wheel = later spool=more lag=max boost later in the rpm band=lower low end torque.

 

Without knowing what the comp wheel is, you could throw the whole thing out of whack is what it might do. Pushing the turbine side size up might send the comp side out of its efficiency envelope at the higher revs, which is the main worry. The turbocharger is a two-part problem that needs both ends to be considered when trying to reach any solution. And then you have the proportion of flow through the turbine and the gate, which might be as simple as a change in gate cycle at the ECU, or a new spring that goes with it(normally the tune is good enough, unless yer making HUGE boost)

Upping the comp side without knowing what the turbine side is doing can at times have the opposite effect: the comp side may never reach its max efficiency and therefore you'd be better served going down in the comp wheel to get your drivability back.

So yer, its either test on your own to develop your own solution, or depend on someone who has done all the homework for you and buy off-the-shelf. Note that not every off-the-shelf turbo does what it claims: the FP Red and Green are not as effective or drivable overall as say, ATP's Evo Gold. And FP markets the sh*t out of these things.

 

Wow! Lets play guess the Turbo and its specs! Like everyone said, in general a larger turbine wheel with less blades will increase spool time and depending on the turbo may or may not increase top end HP and Torque. The KEY is in sizing the turbo's A/R, Trim, Turbine wheel and compressor inducer/exducer sizes to your engine and its modification level.