ok, so I was told that this turbo is a bit bigger than the legacy turbo, correct? So if people are using the legacy turbos on their RS's, the wrx turbos should do fine, right?
The WRX should work fine if you can get the WRX OEM Up/Down Pipes to fit into your RS (or have custom one's made). I think that there are several people undertaking this type of project. As far as 5 psi, you would need to get some type of new wastegate, since the spring in the TD04 is set for something around 14 psi. The WRX turbo is probably a little bigger than the Legacy RHB5, but like the Legacy turbo, you will probably run out of steam in the upper RPM range.
get a manual boost controller and set it low and you can keep it around 5 psi. as for when you hit the upper range, the turbo will run out of steem so you won't have the top end like with a garrett t3/t4 or vf23.
The way I see it. If a TD04 from a WRX can flow enough air for 217hp on a WRX, it can flow enough air for 200+ hp on a 2.5. It is a little bigger than the RHB5, I've actually had both installed on my car, but have not run the TD04 since it's not mine.
If you go that route, I have some of the parts you will need on my site. You might also check my turbo parts list for recommended parts for the swap you are considering. A basic setup with this turbo will run around $1500.
I have one up pipe in stock for $200 if you are interested and can have a downpipe in about a week. I'd suggest Jet-Hot coating though.
Oh, and AZ Scooby is right, you can raise boost with a boost controller, but you can't lower it any less than the spring setting. I explain that on my site under the FAQ.
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