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Discussion Starter #1
I am running EM @ 17.5psi and a COBB DP with cat but I still have the original STi cat-back exhaust. How much more power am I missing by not running an aftermarket 2.5" or 3" exhaust? I wanted to keep the car quiet but if I can gain 10-15hp from a full TBE it might be worth the hurt ears!

Anyone know?
 

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Stee said:
The catback isn't going to make much of a difference- the DP is the best way to make power, especially catless.

tests have shown little hp gain differences between going with a catless downpipe over catted. im looking for little noise so i will probably go catted.
 

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I have nearly the same set up - I do not believe based on COBB's statements that a full TBE will do more than a K&N panel filter would to your HP.


COBB was pretty unspecific when asked exactly how much a Stage II install would suffer sans a full TBE
 

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import111 said:
A catback on an STI gains 8-15whp generally.
8-15 WHP sounds quite high for a catback. Maybe crank but definitely not whp.
 

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JJ18Sniper said:
8-15 WHP sounds quite high for a catback. Maybe crank but definitely not whp.
I'm totally with Sniper here. Not much gain if any without proper tuning. No, I'm not saying tuning is required here either.
 

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A magazine dynoed a bunch of catbacks on a WRX a while back. The results would be about the same on an STI.

Factory Subaru
Manufacturer Factory Subaru
Type Stock
MSRP $715.00
Weight 37.4 pounds
Tip Diameter dual 72mm tips (2.834 inch)
Sound Decibel @ Idle 87dB
Sound Decibel @ 3000 rpm 86dB
Peak Horsepower 191. 8 Hp @ 5600 rpm
Peak Torque 197.1 Tq @ 3800 rpm
Largest Horsepower gain over stock N/A
Largest Torque gain over stock N/A
Piping Diameter 52mm (2.047 inch)
--------------------------------------------------------------------------------


5Zigen
Manufacturer 5Zigen
Type Fireball
MSRP $700.00
Weight 31.3 pounds
Tip Diameter 100mm (3.937 inch)
Sound Decibel @ Idle 98 dB
Sound Decibel @ 3000 rpm 105 dB
Peak Horsepower 198.7 Hp @ 5625 rpm
Peak Torque 201.3 Tq @ 4400 rpm
Largest Horsepower gain over stock 12.0 Hp @ 4400 rpm
Largest Torque gain over stock 13.7 Tq @ 4400 rpm
Piping Diameter 70mm (2.756-inch)
Exhaust System Construction Polished stainless steel canister with coated mild-steel piping.
Source 5Zigen USA, Inc., (310) 608-5575

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Manufacturer Tanabe
Type Racing Super Medalion
MSRP $650.00
Weight 24.0 pounds
Tip Diameter 100mm (3.937 inch)
Sound Decibel @ Idle 101 dB
Sound Decibel @ 3000 rpm 107 dB
Peak Horsepower 197.7 Hp @ 5600 rpm
Peak Torque 199.6 @ 3600 rpm
Largest Horsepower gain over stock 8.7 Hp @ 4200 rpm
Largest Torque gain over stock 10.1 Tq @ 4200 rpm
Piping Diameter 70mm (2.755 inch)
Exhaust System Construction Polished stainless steel canister with stainless steel piping.

Source Mackin Industries (Tanabe Distributor) (562) 946-6820

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Manufacturer Blitz
Type Nur-Spec Racing
MSRP $698.00
Weight 37.2 pounds
Tip Diameter 115mm (4.527 inch)
Sound Decibel @ Idle 104 dB
Sound Decibel @ 3000 rpm 103 dB
Peak Horsepower 200.2 Hp @ 5600 rpm
Peak Torque 204.2 @ 3725 rpm
Largest Horsepower gain over stock 13.9 Hp @ 4400 rpm
Largest Torque gain over stock 15.3 Tq @ 4400 rpm
Piping Diameter 80 mm (3.150inch)
Exhaust Construction Polished stainless steel canister and piping
Source Blitz North America, (714) 777-9766

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Manufacturer GReddy
Type Evolution
MSRP $699.00
Weight 37.4 pounds
Tip Diameter 115mm (4.527 inch)
Sound Decibel @ Idle 94 dB
Sound Decibel @ 3000 rpm 92 dB
Peak Horsepower 200.9 Hp @ 5600 rpm
Peak Torque 201.6 @ 4600 rpm
Largest Horsepower gain over stock 9.8 Hp @ 4600 rpm
Largest Torque gain over stock 10.6 @ 4600 rpm
Piping Diameter 80mm (3.150 inch)
Exhaust System Construction Polished stainless steel canister with coated mild steel piping
Source GReddy, (949) 588-8300
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Manufacturer Cobb Tuning
Type N/A
MSRP $575.00
Weight 26.6 pounds
Tip Diameter 90mm (3.543 inch)
Sound Decibel @ Idle 97 dB
Sound Decibel @ 3000 rpm 103 dB
Peak Horsepower 200.0 Hp @ 5600 rpm
Peak Torque 202.7 @ 4000 rpm
Largest Horsepower gain over stock 12.6 Hp @ 4400 rpm
Largest Torque gain over stock 14.1 Tq @ 4400 rpm
Piping Diameter 75mm (2.952 inch)
Exhaust System Construction Polished stainless steel canister with stainless steel piping.
Source Cobb Tuning, (972) 771-1555
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Manufacturer Supersprint
Type N/A
MSRP $850.00
Weight 29.0 pounds
Tip Diameter 90mm x 145mm Oval Tip (3.54 inch x 5.70 inch)
Sound Decibel @ Idle 95 dB
Sound Decibel @ 3000 rpm 101 dB
Peak Horsepower 198.0 Hp @ 5700 rpm
Peak Torque 201.3 Tq @ 3700 rpm
Largest Horsepower gain over stock 12.2 Hp @ 4400 rpm
Largest Torque gain over stock 13.7 Tq @ 4400 rpm
Piping Diameter 63.5mm (2.500 inch)
Exhaust System Construction Polished stainless steel canister and piping
Source Supersprint, (800) 648-7278
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Manufacturer HKS
Type Hi-Power
MSRP $670.00
Weight 30.7 pounds
Tip Diameter 120mm (4.724 inch)
Sound Decibel @ Idle 97 dB
Sound Decibel @ 3000 rpm 102 dB
Peak Horsepower 202.9 Hp @ 5625 rpm
Peak Torque 204.9 Tq @ 3650 rpm
Largest Horsepower gain over stock 13.1 Hp @ 5620 rpm
Largest Torque gain over stock 13.6 Tq @ 4200 rpm
Piping Diameter 75mm (2.952 inch)
Exhaust System Construction Polished stainless steel canister with [email protected] mild steel piping.
Source HKS USA, Inc., (310) 491-3300
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Manufacturer A'PEXi
Type GT Spec.
MSRP $749.00
Weight 26.2 pounds
Tip Diameter 115mm (4.528 inch)
Sound Decibel @ Idle 100 dB
Sound Decibel @ 3000 rpm 104 dB
Peak Horsepower 201.1 Hp @ 5625 rpm
Peak Torque 201.5 Tq @ 4600 rpm
Largest Horsepower gain over stock 9.9 Hp @ 4600 rpm
Largest Torque gain over stock 10.6 Tq @ 4600 rpm
Piping Diameter 75mm-85mm (2.953-3.346 inch)
Exhaust System Construction Polished stainless steel canister and piping
Source AÕPEX Integration (714) 685-5700
---------------------------------------------------------------------------------

Manufacturer Skunk2 Racing
Type N/A
MSRP $599.00
Weight 30.6 pounds
Tip Diameter 100mm (3.937 inch)
Sound Decibel @ Idle 102 dB
Sound Decibel @ 3000 rpm 106 dB
Peak Horsepower 199.3 Hp @ 5625 rpm
Peak Torque 203.6 Tq @ 3600 rpm
Largest Horsepower gain over stock 13.0 Hp @ 4400 rpm
Largest Torque gain over stock 15.7 Tq @ 4400 rpm
Piping Diameter 75mm (2.953 inch)
Construction Polished stainless steel canister with stainless steel piping.
Source Skunk2 Racing, (909) 808-9888
--------------------------------------------------------------------------------

Manufacturer MRT Performance
Type N/A
MSRP $795.00
Weight 30.5 pounds
Tip Diameter 100mm (3.937 inch)
Sound Decibel @ Idle 96dB
Sound Decibel @ 3000 rpm 104 dB
Peak Horsepower 198.8 Hp @ 5700 rpm
Peak Torque 202.8 Tq @ 3675 rpm
Largest Horsepower gain over stock 13.6 Hp @ 4400 rpm
Largest Torque gain over stock 15.5 Tq @ 4400 rpm
Piping Diameter 75mm (2.953 inch)
Construction Polished stainless steel canister with stainless steel piping.
Source Renick Motorsports (MRT Dealer), (714) 871-9300
---------------------------------------------------------------------------------

Manufacturer M2 Performance
Type N/A
MSRP $795.00
Weight 34.9 pounds
Tip Diameter dual 76.2mm (3.00 inch)
Sound Decibel @ Idle 94dB
Sound Decibel @ 3000 rpm 94dB
Peak Horsepower 195.9 Hp @ 5700 rpm
Peak Torque 198.9 Tq @ 3675 rpm
Largest Horsepower gain over stock 7.1 Hp @ 4200 rpm
Largest Torque gain over stock 8.7 Tq @ 4200 rpm
Piping Diameter 76.2mm (3.000 inch)
Exhaust System Construction Polished stainless steel canister with stainless steel piping.
Source M2 Performance, (925) 686-9047
-------------------------------------------------------------------------------

Manufacturer Thermal Research & Development
Type N/A
MSRP $694.95
Weight 26.2 pounds
Tip Diameter 80mm x 111mm (3.150 x 4.370 inch) oval tip
Sound Decibel @ Idle 101 dB
Sound Decibel @ 3000 rpm 108 dB
Peak Horsepower 198.3 Hp @ 5700 rpm
Peak Torque 201.1 Tq @ 4300 rpm
Largest Horsepower gain over stock 11.4 Hp @ 4400
Largest Torque gain over stock 13. 4 Tq @ 4400
Piping Diameter 76.2mm (3.000 inch)
Exhaust System Construction Polished stainless steel canister and piping.
Source Thermal Research & Development, (818) 998-4865
----------------------------------------------------------------------------------
 

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Nice way to back up your claims import, but i really believe those numbers must be inflated. I've yet to see a dyno graph show a catback truly making that extent of a difference. The downpipe is what opens up the power, but catback has been known for noise and modest power increases. Obviously the larger turbo and more modded you go the the more the catback becomes a bottleneck on the system.
 

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import111 said:
As I said before, this was done on a dyno. Those #'s are to the wheels.
If this was the case those numbers would be labeled WHP and not HP which usually means at the crank.
 

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JJ18Sniper said:
Nice way to back up your claims import, but i really believe those numbers must be inflated. I've yet to see a dyno graph show a catback truly making that extent of a difference. The downpipe is what opens up the power, but catback has been known for noise and modest power increases. Obviously the larger turbo and more modded you go the the more the catback becomes a bottleneck on the system.


I have seen some dyno plot automatically correct for estimated driveline loss - maybe the dyno mentioned is using correction? The numbers do sound too big for WHP :p
 

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If it is not whp and it is crank hp than why is the stock WRX 191. 8 Hp @ 5600 rpm
Peak Torque 197.1 Tq @ 3800 rpm. Wouldn't it be 227hp? Trust me, all the runs were done on the same dyno with the same car in the same week. I use to have the Turbo Magazine with the exhaust shootout that these #'s came from.

Just cause a catback adds 5whp to a Civic doesn't mean that's all your gonna see on a turbo car. However I have seen 1 catback dyno that on;y gained 3whp on a WRX (I don't remember the brand of exhaust).
 

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Discussion Starter #18
JDM-STI said:
I'm sure those are crank HP/TQ ratings. That's not much at the wheels. Good post though:)
Yes that is a good post and even if the gain is at the crank I would be happy to ditch my stock STi catback for a 10hp gain! However the WRX has a 2.25" catback vs the 2.5" on the STi so I am not convinced that an STi would pick up as much power. Anyone else?
 

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The cat-back makes HUGE gains on the *WRX*. It is MINIMAL on an STi.

Putting an oem STi cat-back on a WRX makes a HUGE improvement.

The gains from doing a big high-flow cat-back on an STi are going to depend on it's impact on boost creep. Some cars are going to gain less than 0.5 pounds, and likely less than 5 whp. It you do gain some creep, it could be more, but it could be BAD when it gets colder...

If you are happy with the sound on the stock cat-back, keep it. If and when you want more sound, then start researching cat-backs...

SS
 

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Discussion Starter #20
Subaru of Gwinnett said:
The gains from doing a big high-flow cat-back on an STi are going to depend on it's impact on boost creep. Some cars are going to gain less than 0.5 pounds, and likely less than 5 whp. It you do gain some creep, it could be more, but it could be BAD when it gets colder...

If you are happy with the sound on the stock cat-back, keep it. If and when you want more sound, then start researching cat-backs...

SS
This makes sense. I would like a bit more sound than the stock cat-back gives so I am in the market for a quiet aftermarket system, probably the EVO2. I will be happy if the car gains 5whp and spools a little faster - am I dreaming?
 
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