well, i'm not exactly sure. but i ordered a magnaflow muffler for my car. but being that it is a 2011, the guys at the muffler shop couldn't make it fit. we tried two different mufflers and they were both too long. apparently scion moved some under carriage stuff around this year and made it tough to fit.

so....i decided to go with straight pipe and no muffler. i love it!! saved me like $150 and i think it actually sounds better. pretty loud on acceleration, but settles out nicely when driving down the highway. performance is the same, at least not enough difference to notice. has a nice deep tone, not the real high pitched "pissed off bumblebee" you hear on some other cars.

if you want to save some money and get good sound, i would recommend the straight pipe with no muffler.

The muffler wouldn't create much if any issues relating to back pressure due to the CAT. Most to all back pressure to the engine will be created between the cat and the engine. muffler purely muffles sound. I have run with no muffler on this and a 1st gen xb with no issues. Been that way pretty much since bought the car. I have no ill affect in performance.

I have run multiple vehicles with no muffler some trucks with straight pipe and open headers. with no major issues other than loud and obnoxious on some and maybe some performance drop. but that I don't mind lol. except this car is my wife's and I am not running it like that. Most 4banger do not benefit from striaght pipe without mods.

but v8 can in some cases improve with straight piping.

but issues with straight piping is laws regarding emissions. if you straight pipe and remove the CAT you are in violation. You can remove the muffler without violation other than possible sound ordinance if metered, but as far as emission muffler does not effect emissions.

---------- Post added at 01:46 PM ---------- Previous post was at 01:33 PM ----------

Basically the perfect exhaust would be one that creates the perfect "suction effect" for lack of terminology. It would just be the right size to allow air to move while creating enough pull (suction)from the cylinder to make sure it gets all spent gases out. To small or restrictive and the gases can't escape quick enough and the flow will be slow because of lack space to move and rob performance. To big or to little restriction and the flow will be slow because it is only being puched out by the piston movement thus creating no suction effect which can cause the gasses to move out slowly and not fluidly and again can cause loss of performance.

Yeah our cars with no muffler do not really sound that bad, since we have resonators built into the exhaust it helps cut down on annoying rasp you normally hear with open exhaust 4 bangers.