[Eastmeetswest]

So I slapped a Remus on and love the sound and all and was not doing that one for performance but thought it would compliment an intake nicely for sound and a bit of performance for the extra air coming in. But it is only a muffler pretty much with a pipe out one end and the nice tips which are beautiful.

But is it the muffler that is the restrictive part on a exhaust or is it somewhere upstream (providing you keep stock headers and such) like the y-pipe area. I figured a stock muffler would be somewhat restrictive for sound and emission reasons so some increased flow makes sense witha muffler but who knows

[Str8EJ]

increase in plumbing dia.
the muffler doesn't do jack for the flow of exhaust gases, only attenuates sound.
for an all out performance exhaust, you probably wouldn't need a muffler at all.

[PresaMat]

The stock mufflers are rather restrictive - also the cats kill power, shitty bends in the pipes, etc etc. From the headers down factory exhaust is very restrictive.

[jjhan85]

damn...too bad headers and stuff are hella expensive!

[esbezee92]

obviously its a little different with the 335i because its a turbo, but how much could you expect from a barely street legal exhaust on a non-turbod e90/2, i know people dont make much or any power from bolt on exhausts, but would a full on custom exhaust yeild some worthwile gains?

[SE3P_to_E90]

If you want the most power, take out all exhausts and put a straight pipe in it... it will probably make you def, but you'll yield the most gains.

Full exhaust systems are known to release noticeable power -- butt dyno... but usually, those exhaust systems (once again, since you're taking out the restrictive flow patterns) will be extremely loud.

Taking one example...
In my rx8... gains are extremely minimal -- b/c of the small 1.3, 2rotor engine... you really have to PUSH the car to get power. My HKS intake (the most expensive and best one out), yields .5-2hp MOST. my borla cat-back yields 3-5hp. With that combo, the car sounded great, and i "thought" it was faster, but that's all debatable -- butt dyno -- etc... plus the loudness makes the car "seem" faster... if you get what i'm saying

Then i put in the RP highflow cat (basically the midpipe with a small cat.converter)... that yields 8-10hp, and that was noticeable... that was the extent of power... i also put in a piggyback unit, but that was a huge Pain in the ass b/c it had to be tuned at every nook and cranny... adjusting and playing w/ AF ratios, etc... after a full days work of scrutinous tuning, that yields 15hp...

All those mods, were decent... not great. the canzoomer piggyback, i would never do again -- b/c it's a waste of my time. as for the exhaust, intake, midpipe, those were the best bang for buck mods... not because they yield the most power, but b/c they made my ride "feel" incredible -- the sound, attention, etc.

If you want true power, you'll have to go Forced Induction... my last mod for the rx8 was a greddy turbo... i ran approximately 15psi, and that yields about 40whp... you can really feel that badboy... but, custom mods lead to custom problems... and one bad vacuum hose lead to detonation, and eventually my rear rotor failing...

Don't expect your car to ever truely feel like a 335i... instead, just enjoy your ride every minute. and worst comes to worst, you can still bash on 325's and 328's lol

[Mr. M]

5 replies and not a single word about scavenging theory, flow dynamics, backpressure, resonance

OP. google it or use howstuffworks

[lux.sh]

Originally Posted by Eastmeetswest

So I slapped a Remus on and love the sound and all and was not doing that one for performance but thought it would compliment an intake nicely for sound and a bit of performance for the extra air coming in. But it is only a muffler pretty much with a pipe out one end and the nice tips which are beautiful.

But is it the muffler that is the restrictive part on a exhaust or is it somewhere upstream (providing you keep stock headers and such) like the y-pipe area. I figured a stock muffler would be somewhat restrictive for sound and emission reasons so some increased flow makes sense witha muffler but who knows

www.howstuffworks.com

Generally, in an exhaust system, cats restrict the flow the most. then resonators. Crappy exhaust bends play a role in this one too.

Most ideal setup(meaning, keeping the vehicle street legal & sound legal) is putting on proper high-flow cats, maybe small unrestrictive resonators with a nice muffler. Of course, bigger diameter straight piping will be required. Don't go too big in diameter. Thats when backpressure issue pops up and there has been billions of stories on whether backpressure is good or not. So far, no definite answer.