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larger diameter exhaust systems that are cat back can increase you exhaust flow slightly. better breathing engine is a happier engine to an extent
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replacing the muffler will give you nill performance gains ... cat-back replaces all the pipes between the catalytic converter and the muffler ... allowing better exhaust flow from the cats out as mentioned above ... efficient exhaust flow means ~5hp in gains ... combine with high flow cats and you get better gains, ~7 - 10hp combined ...
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Originally posted by Chooch@Dec 14 2003, 01:57 PM replacing the muffler will give you nill performance gains ... cat-back replaces all the pipes between the catalytic converter and the muffler ... allowing better exhaust flow from the cats out as mentioned above ... efficient exhaust flow means ~5hp in gains ... combine with high flow cats and you get better gains, ~7 - 10hp combined ...
i agree. and the catbacks usually install at a bolted flange point which makes for no welding or cutting requirements resulting in a cheaper/easier modification. i think cat-backs are great mods, well worth the couple quid extra due to the increased exhaust efficiency not only resulting in modest hp gains but also in custom looks and sound.
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most exhaust systems only add more performance noise than performance itself. usually when mod like this are done yes you do gain HP (very little i might add) but you usually gain that performance from the bottom end , your changing the breathing structure of the car, thus changing the air flow dynamics and the HP curve changes as well. typically on an everyday driver you wont see much in the way of performance gains. the only time that i can think of where an exhaust system actually is a good mod to do is if you force your car or if you car is of high HP to begin with. ie-that red corvette in the post above mine.
here is a dyno of one of the biggest gains youll get on an e36 M3 you can see that bottom end is lost and top end is gained (but mid range is quite good) and also note that the gains arent that much to begin with, this chart is one of the highest i have seen for a simple exhaust mod. only 6.3hp gain i think
True Furious, but that's using a car that has been tweaked to the max allowable as it is. The M3 is a car built specifically for performance, so it's already got the most efficient exhaust design allowable by law (thus no straight pipes and the cats have to be factored in). Also keep in mind that the M has dual exhaust pipes.
When you take a car that isn't as engineered as the M, I'll use (Oh the HORROR) an Integra as as example (but you can use just about any non-performance oriented car here) and change the exhaust the right way you will get more gains than that. I have seen Dyno plots of Integras gaining as much as 10 horses (rare however, mostly the average was 8) and almost comparable torque.
The trick is to acurately match your exhaust diameters to maximize airflow from the engine out. The more efficient you expel exhaust the better performance you will get out of your car. From what I remember, exhaust gasses are expelled in pulses. Too big of a diameter and your pulses don't expell efficiently causing exhaust gasses to actually re-enter the combustion chamber. Too little and you have too much back pressure due to the build up of pulses on their way out.
Anyway, where was I going with this .... oh yeah, if you match a set of high flow cats with your cat back exhaust on your car you will get better gains than what you've got posted obove Furious. I'm not saying you'll be outrunning M3s! For God's sake calm down. I'm saying more than 1 - 2 horses. Add a set of aftermarket performance headers and it gets better. Do a complete hookup - Headers/Intake/Cats/Exhaust and you'll have very noticeable gains.
I think I'm done here.
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