Ok I have come across a turbonetics t3/o4e 57 trim w/ .48 A/R Turbine. I want to get a bigger exhaust housing(a .63) A/R. Any draw backs? Also, I'm trying to compare it to a t3/o4e 50 trim w/ .63a/r. Anny differentces?

P.S.
I would have gone and read it at turbonetics site, but I do cannot read compressor maps. Also, I've searched already

I think for the SR20 it's a 50 trim with a .83 for max power.

The thing is I don't want max power. What are some Positves and negative with a .57 trim and a .50 trim?

high comp motor or low comp motor. if high the .63 is much better. slightly slower spool up, but better top end. the .82 ar housing is best for max hp, but is the slower spooling of the 3 housings. More info to help

I have a BB motor with s4 cams for internals

I hope this settles it for you Dan. The 0.48 A/R turbine housing is too small for the SR20 motor. The turbo will be very choked by backpressure at high RPM. You should use at least a 0.63 A/R housing in this case. The Stage III exhaust that you have in there is fine.

As for the compressor side, the 0.60 A/R compressor housing is okay, as compressor housing A/R does not affect power or spoolup very much. The 57 trim compressor wheel is too big for the 0.48 A/R turbine housing. This results in a turbine/compressor mismatch. As such, the turbo will not be very efficient. It will not make very good power and top end will suffer. If you buy this turbo, I would switch to the 0.63 A/R turbine housing (or 0.82 A/R for max power) and step down to a 50 trim compressor wheel. It has been shown that the 50 trim wheel is very efficient and kicks ass. This will also require a new compressor housing machined for the smaller compressor wheel.

Conversely, you can switch to a Stage 5 wheel in the 0.63 or 0.82 A/R turbine housing and you will have one hell of a turbo. This will allow you to keep the 57 trim compressor wheel. By the time you factor in the costs of making these changes, they will negate any savings you had in buying the wrong turbo for $300.

I think you will be quite happy with the T25 and the porting/Extrude Honing I am doing for you.

I hope you are a believe now.

Peace out,