I have a Greddy Ti exhaust and want to achieve more hp. But I want to ask 2 questions.
1.What kind of hp gains did you get for adding a downpipe?
2.Would you recommend spending the money and installing a 02 Housing Turbo Outlet for a stock turbo?

 

I say a DP would be a great addition. I added my Helix DP & Helix Test Pipe after I installed my HKS Carbon Ti exhaust, and the butt dyno said the car felt more responsive. I don't know how much more power it added, but it did feel more "motivated", and the turbo seemed to spool a little quicker.

I have no idea about the O2 housing....

 

any turbo car, getting all the piping done really helps the car bring out its true power out.

I heard the 02 housing is good to a certain high horsepower (lik 400whp).

I also heard replacing the 02 housing isn't all that good unless you have a lot of power. That and it's pia to fix the cel problem with the o2 sensor, unless you go ems or something better.

 

No, it isn't worth it.

 

why is that?

 

the stock o2 casting is pretty good. Wastegate flow is kept separate from turbine flow for several inches until they are merged before the downpipe. The passages for both wastegate and turbine flows are pretty large, compare to a 2g eclipse. It should be sufficient for the stock turbos air flow capabilities, but an upgraded turbo with higher flowing abilities and I can see how it would be a restriction, but most turbo upgrades necessitate a new outlet casting anyways.