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Discussion Starter #1
I'm thinking ahead for next season and an exhaust mod is on my list of things to do. I doubt anyone will see big gains (>5hp) with catback swaps. So it's hard to justify spending much money for this.

What I'm wondering is if a cut-out just beyond the last cat might give decent gain at low cost. It would also be nice to close off the cut-out when on the street. One really cool set up I saw on a Z-28 was a cut-out you could open and close from the cockpit. I priced it out when I had a Z-28 myself and it would have been less than $200. for everything except installation.

Anyone have any knowledge about the impact of a cut out on turbo cars?

Thanks in advance for any help, Danno :D

http://www.quicktimeperformance.com/qtec.htm , here is an example, they even have a video of one on an impreza WRX, but on that particular car they placed the cut out on the down pipe.
 

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I was at an autocross in Las Vegas over the weekend and one of the STi owners had completely removed the muffler on his. It was replaced with a straight pipe. Don't know about the power, but the thing sounded totally awesome! Quiet at idle, but sounded really great at WOT! Only other engine mod he had was a K&N filter. There were 4 STis at the event and the 3 cars with the stock mufflers sounded tame by comparison.
 

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Guru pulled the exhaust on his after other work was done and didn't see any power gain, actually lost power I believe.

The gains in exhaust aren't the exhaust itself. If you could get away with a stealthback and replace from the turbo back to the exhaust, there's where all the power is. A stealtback with new muffler ~30hp. Stealthback with stock muffler ~26hp.

I wouldn't spend any time worrying about the rear section itself other than for sound reasons.
 

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Discussion Starter #4
Yeah, the benefits of modifying or bypassing the catback section would make it sound different and likely better, but I suspect there's not much if any improvement in power. I suppose if I had a cutom straightpipe installed without muffler I could drop 20lbs or more and improve the sound :D On my WRX I had a guy build a custom axle back with nice tip for under $150, it sounded awsome. Keeping the resonator intake while removing the muffler appears to sound better than catback straightpipe IMHO :)
 
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