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Old 03-04-2002, 03:08 PM   #1
Scooby Newbie
Member#: 5738
Join Date: Apr 2001
Location: Ontario, Canada
2002 WRX Sedan
Sedona Red Pearl

Default Merit (performance-wise) of catback exhaust

I am thinking about getting a catback exhaust system. But I am still a bit confused on the performance merit of such a system.

Do you get the catback mainly just for looks and sound?

What kind of performance improvement would you see? I looked at some dyno numbers for the Scoobysport catback and results seem to be mixed (mostly no performance gains at all). And I also heard that with a freer-flowing catback, the low-end torque might be compromised due to less backpressure.

I know this topic has probably been beaten to death by you experts out there...and there seemed to be a lot of conflicting opinions when a search is performed (at least when I did a search). And my browser is unable to view the exhaust website hosted by atf78.

If there is indeed performance advantage to installing a catback, it would be great if someone can come up with a performance/loudness ratio comparison chart for the different catback systems.

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Old 03-04-2002, 06:50 PM   #2
Scooby Guru
Member#: 4414
Join Date: Feb 2001
Location: Dublin, CA
2002 WRX Sedan
Midnight Black


shiv was cool enough to show us this dyno plot comparing his Stage 0 configuration, and what happened when he threw on a catback (SPT optional muffler)

The highest HP run is with the muffler

You can see that the range in which the catback showed improvement is from about 4500 to 6500, and it's not a huge increase, but a reasonable increase. This is already with all the improvements of Stage 0, so I'd guess that the effect is larger than it would be with the stock exhaust tract.

I'd expect it would have a bigger improvement if a less restrictive downpipe were used. However, in all cases I'd expect gains primarily in the higher RPM range...4000 - 4500 RPM and up. No real gains in the lower half of the RPM range.
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Old 03-04-2002, 06:54 PM   #3
Scooby Newbie
Member#: 14475
Join Date: Jan 2002
Location: Northern Virginia
02 WRX



Really... there is not much merit too it... there are very minimal horsepower gains to be had..depending on the catback system you install... you can expect 4 to 6hp in gains from a good hi-flow system. This is hardly worth your hard earned $$$ on a WRX considering the 400 to 600$ costs of a cat-back. Mark from TurboXS was honest with me on the phone when I ordered the Unichip/boost controller/drop in K&N and told me that the cat-back was only worth 5-6hp over the stock kit with their Stage 1 kit.

Do yourself a favor, and get a unichip and boost controller setup...without the cat-back exhaust. You will get 4-5 times the horsepower gains offered over just the catback for 750-800$.

Shiv from Vishnu also offers a similar setup but had no "plug and play" harness like TurboXS to make things sweet and simple.

I have been running the TurboXS stage 1 unichip and boost controller for over 6 months and love it... great power gains, easy mod to install.... well worth my $$$.

Some guys would just tell you to install a 45-50$ boost guage and 50-100$ manual boost controller for similar gains... I myself like the added security of the Unichip that adds the necessary A/F ratio and Timing curve changes for added boost.

UP to you... Good luck!

02 Subaru WRX... TurboXS Unichip
99 Vortech Mustang GT.... way too many mods to list...
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Old 03-04-2002, 08:16 PM   #4
Vishnu Performance
Member#: 14494
Join Date: Jan 2002
Location: SF Bay Area, California
WRX Porsche 996
blue & black


The SPT rear muffler section was worth, on average, an additional 8 wheel hp over Stage Zero with no additional Unichip mapping. Torque was higher across the board too. Those are pretty significant gains for just a muffler section. I suspect there's another few hp if I had retuned the Unichip and replaced that skinny stock intermediate exhaust pipe with a larger-diameter unit. But even if one just replaced the muffler section, he'd see some good bang for the buck ($300-odd for another 8 wheel hp). Of course, these predicted gains are for a car that is already flowing more air than stock.

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Old 03-05-2002, 01:06 AM   #5
Ken C
Member#: 6605
Join Date: May 2001
Location: PA, USA
Default Cat backs

To echo some comments here:

A good cat-back will add hp to the high end of the car, as seen in the plots. The ScoobySport has done anywhere between 9 and 14 hp in dyno runs that we have seen, but mainly to the top end of course. The real increase in driveability and low end torque comes in through other methods like deleting cats and using a good downpipe, as with our full exhaust, or by taking an careful approach like Shiv has done with his stage O.

You really can't just gloss over the cat back saying that it doesnt help, as it is part of an equation (increase low and midrange torque, increase high end hp, etc)

To say it again:
We don't recommend increasing boost without good engine management coupled with it, by the way, and I think others here would agree.

Rally Performance
ScoobySport N.A.
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