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New 08 owner, loving the car, told by dealer that catback is available for a good price. Is this a mod that will increase performance or is it only about the sound?
 

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It increases performance as well as sound due to larger diameter of the exhaust and design of the muffler. The SPT system deletes the resonator located in the stock midpipe. If I were you, I would jump on the exhaust before the end of this month when the dealerships jack the prices up to $860.00 +.
 

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From my experience with a variety of turbo small engine cars, the full TBE is what you want for the healthy gains. Im sure the cat back will give you somehting though like 10-15 HP's maybe?
It will sound great though as well. Which will feel like 30hp :)
 

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A cat-back will net you, on a good day, maybe 10hp. Probably less. It's mostly for looks/sound. The stock exhaust is really lame sounding.
 

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on the WRX, minimum gains.... but there should be some. The SPT exhaust diameter isnt much larger than stock. But it makes the right amount of noise IMO. If the price is still the 'intro price', then it wouldnt hurt to go for it.
 

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SPT has a min gain. If you are looking for a low Boxster Rumble that is not going to shake the car next to you, but you get into it and you will hear it.

It is a great choice for the Current price.

For me the SPT is the stepping stone to the TBE, I will be adding a Cobb DP ASAP and a tune. That is where you will get into the real HP gains.

Here is the difference for me between OEM and SPT

 

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well... i hate to sound like a geek here but it is not like adding horsepower as with nitrous, bigger cams or turbo. technically it will not add any horsepower (to the engine) but it will free up hp to go to the wheels (whp) instead of trying to force gases out a restrictive system. freeing up hp and lightening the vehicle weight are excellent ways to boost performance out of a vehicle. lightweight wheels, crank pulleys, high flow air filters, cbe's and dp's are all good ways to increase whp without going into the engine internals. o.k. maybe i did sound like a big stickler ;D

i love the spt on my sedan! it does sound so mean as well. ;)
 

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i noticed that after a while driving with the SPT its feels like its getting stronger, i reset the car on install and after a few week the car ecu seem have to learn
 

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well... i hate to sound like a geek here but it is not like adding horsepower as with nitrous, bigger cams or turbo. technically it will not add any horsepower (to the engine) but it will free up hp to go to the wheels (whp) instead of trying to force gases out a restrictive system. freeing up hp and lightening the vehicle weight are excellent ways to boost performance out of a vehicle. lightweight wheels, crank pulleys, high flow air filters, cbe's and dp's are all good ways to increase whp without going into the engine internals. o.k. maybe i did sound like a big stickler ;D

i love the spt on my sedan! it does sound so mean as well. ;)
Ok, diverging from the topic post a little bit and to elaborate on what REX said.

BHP (brake horsepower) readings are taken on an engine from the crank shaft with just the intake, exhaust and base engine...no accessories, no drivetrain.

WHP (wheel horsepower) is power to the wheels, this a net horsepower reading which includes all losses and gives a true reading of power to the wheels. (even though some dynos read a little high or low depending on the type).

So, changing your exhaust, intake, cams, turbo, and tune will directly effect your BHP rating.

WHP would also be affected logically by BHP increasing mods...but adding things like lightening accessories, light flywheels, etc will only affect the WHP rating, (ie, freeing up power).
 
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