read powerzone coment about muffler.for turbo, just leave it straight thru.the muffler is just for noise restriction.
for N/A set up, the extractor, mid section play the rules.size, shape depends on your engine combustion output.the best set up is to get the exhaust thru out without any pressure and leave a vacuum so that next combustion will be easy thru.so far extractor, 4-1 and CAT is the best.only that noise matter, we need to change to oval.now we're back to square.nothing change.the output mufler, also call a resonator is to reduce noise.thats it.
unless your engine has more than 1 output profile.e.g Vtec, mivec.to make it maximum, you have no choice except to concentrate at second profile (Vtec Open) setup so that you gain maximum performance.with this, you suffer noisy sound.
e.g bullet.
to enjoy improve in performance and still maintain the noise level, just use aftermarket exhaust system like, hotbits etc.they have proven at dyno and noise test.std factory use a blockage type while the aftermarket just release this with S flow concept, enlarge inner diameter and cover up tight with good fiber.
bear in mind, each time you change the exhaust, please do check the tuning.bigger output is not suitable any more for the std tuning.this is why speedwork recommend SAFC together with the K@N open pod to give good combination.the price wise?? errr...rm3+++k for all..expensive!
better stick to std and save money for others.
