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Originally Posted by Ricks15
2.5in wont loose low end tourqe but if you bolt on a big ol Turbo size N1 muffler to that pipeing then you loose backpreasure,
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You want to lose back pressure. Back pressure is a sound deadening effect that prevents your exhaust from getting to loud. All it does is send pulses back up the exhaust sooner than later, which isn't all that good either, unless you like lots of scavaging, or hot exhaust gasses sent back up the EGR into the mani.
Back pressure does serve to maintain good smog emissions, and is no way a performance enhancer to have it. This is true and has always been determined by increased piping diameter as a performance enhancer, or doing to the effect of what is called header out, or cutting pipe where it goes cold.
The fact is I live in Cali so I selected a 2.5" pipe to deaden a little bit of noise, and to keep it lower than 95dB. I understand that perferatted pipe is a sound deadener (resonators) and is associated with back pressure, and pulses to run back up my header and cause flow issues. So I selected a cat back exhaust with no resonators. I just didn't want a 3" horn blaring out the rear of my car, weither it had a resonator or not, i just wanted constant, uninterupted FLOW.
The 2.5" over 3" debate is stupid, bigger is better. It's just the crap added to the CAT back that can make or break a CAT back as a performance enhancer. It's just a matter of what works with purpose over function.
For purpose and function I have selected a 2.5".
But if I didn't need a purpose, and just to serve for function, I would use a 3"....