Running without a muffler

[m3f_M3AutoXR]

My car came with a Hamman exhaust that has been "patched" on the muffler body itself. I was wondering if anyone has run without the muffler and just resonators.



any ideas?? comments?



JM

97 Estoril

[m3f_00poop6x_6dca3456a4]

i believe on OBDII you actually lose about 1-2 rwhp.

[m3f_04M3blur_1ceee0bbd5]

And what about the noise and passing the emissions test?

[m3f_Sirius_880bd69485]

Don't you need 'some sort' of muffler for a bit of back pressure? Or will the catback alone provide that. I was told that an engine needs some back pressure to preform right... running it without an exhaust system would be bad....

[m3f_96M3Power_4547fc3d60]

The car should gain some power by removing the muffler... as long as its past the last oxygen sensor... and as long as the cats are still in place... however you must be careful because now your sending hot gasses right under your rear seat. Maybe get some custom piping and aim in town, but that change in direction is only going to mean resistance, so it might be better to just send it straight out the back. Still there should be a gain and about a 40 lb wieght loss

[m3f_camshaft_3417d47b3e]

Don't you need 'some sort' of muffler for a bit of back pressure? Or will the catback alone provide that. I was told that an engine needs some back pressure to preform right... running it without an exhaust system would be bad....



Yes. The engine needs a little bit a back pressure. The reason is because of the way the headers are arranged. You have two seperate pairs of three primary pipes all merging into one collector. Now remember that the cylinders fire at different times. So one cylinder pushes the exhaust gas out the chamber and down the primary, past the merge and out the back. As that gas rushes past the merge of the primaries, it creates a temporary vacuum on the other two primaries. As this happens then, the next cylinder is in the process of pushing out its exhaust gas. The temporary vacuum created from the previous cylinder then helps **** the exhaust gas out of the second cylinder. You need some resistance in the system to fascilitate this vacuum though. That's why a completely free flowing system can cause a slight loss of power. A really good set of headers takes this vacuum effect into consideration and specifically makes the primaries a certain length to get the best effect.



Now on to the original question. I'm not sure for an M3 in particular. I think the stock headers and cats are restrictive enough that they would provide enough backpressure alone to prevent removing a loss of power from just removing the muffler. This is just my guess though. Also, you could run into resonance problems when you mess with the exhaust like that. I know a guy who custom fabricated a full exhaust system for his Z06, trying to mimick the one in the C5R race car. In short he didn't do such a great job. He had so much resonance that while the car was idling, he had to hold his teeth clenched to stop them from rattling against each other.



Austin

[m3f_camshaft_3417d47b3e]

Oh, sorry. I forgot that "s...u...c...k" gets filterd. Thats the word that went in where the asterisks were.