i was wondering if any one knows if its legal to have your exhaust exiting behind the rear wheel (as in out the side not just in the wheel arch)???

In the old days it was not a drama,had a HZ V8 pano that I did that to & rego was never a prob,but these days most cars have a rear muffler that the tail pipe comes out of-so if you were to mod it as you say then obviously you will be doing without that rear muffler & that could be your problem with the law.
Best to ask an exhaust shop,but make it a well known company as they have more to lose if it is illegal.
Small shop may say its ok just to get your cash.
These are my opinions & anyone with more knowledge of this please feel free to correct me.
Cheers, Dave.

Basic QLD rules are here, see if you can make sense of the bit about exhaust outlets cause i cant?

http://www.transport.qld.gov.au/resourc ... icles2.pdf

this may help you out it may not but here in Victoria the exhaust may exit on the side as long as it is more than 30 cms back from the last door/opening of the passenger cabin.

i heard the same thing but 100mm ive got a 3" twin tip cannon im wanting to put on it so that might count as a rear muf

i know it has to be 6' away from your nearest opening. thats for nsw