I've read articles on IS350 dynoed with HKS HiPower with 7 WHP gain, so a 250 would probably be like 5WHP

 

No exhaust alone with produce gains of 12-18hp,

You will get 5-7hp and you wont notice the difference. If you do, your confusing sound for power

 

An axle-back exhaust for our cars are not the most restrictive part. It's especially the catalytic converters right after the headers and then midpipe. You can refer to the link on the gains for the f-sport exhaust which is essentially a re-branded hks axle-back exhaust. http://www.importtuner.com/powerpage...s/viewall.html

 

There is a vendor marketplace and classifieds section for this

https://www.clublexus.com/forums/clu...rketplace-118/

https://www.clublexus.com/forums/is2...assifieds-173/