if I were to get a custom set up should I buy the mandrel bends and take it to them and have them put it on or just not mess with it and just have the piping 2.5 and have it flow around what a 2.25 would....also I have a muffler that has a 2.25 inlet and having 2.5 welded on wouldn't the inlet bein a lil smaller help keep some backpressure for low-end torque......just a thought thanks

ok let me start with your backpressure issue...from what i have seen, heard, read, and felt with my own car the whole backpressure and torque thing is crap..i went from stock to 2.5" madrel bent and didn't notice any difference in low end..i could still burn the tires with ease...the easiest was to do a custom exhaust is to find a shop that has a mandrel bender and have them make you an exhaust...and having a muffler with a 2.25" inlet basically kills the whole rest of the exhaust since the gases will have a nice free 2.5" to flow then have to bottleneck into a 2.25" muffler..best thing is to sell that one and get a muffler with at least 2.5" inlet...

is it cheaper to go to a muffler/exhaust shop?

damnit nooB...read the post before you respond... here is a direct quote from my post...

"the easiest was to do a custom exhaust is to find a shop that has a mandrel bender and have them make you an exhaust..."

no one does mandrel bends thats y I said should I buy the bends and have them weld it......I already have the 2.25 inlet muffler and I like how deep it is......

Go to a realiable muffler shop.
Make sure they don't use those pre-crushed bends.
Get a flange welded to a 2.5" pipe and have them work from the cat to the muffler.
You're right, a 2.5" pipe will probably end up being around 2.25" in the bent areas. However, this will only cause turbulent flow because the gases will be going from larger to smaller diameter sections in several areas. Since you already have your muffler, just go ahead and do it.
It shouldn't cost you more than $200 for the pipe/hangers/welding.

If the shop doesn't do mandrel bending... any of these will be better than a custom exhaust:
http://search.ebay.com/ws/search/SaleSearch?from=R8&ht=1&sasaleclass=2&satitle=eclipse+cat+exhaust&sbrbin=t&sokeywordredirect=1&sosortorder=1&sosortproperty=3

This is so ricey man. ;) LOL

First of all, this has been discussed dozens of times - there is no such thing as good back pressure! You can have acceptable levels of back pressure since it's nearly impossible to remove it completely, but exhaust system performance is a measure of exhaust gas velocity. You don't want any back pressure, you want the exhaust gases to get the fuck out the tail pipe as fast as possible. The faster they exit, the easier your engine can exhale. Exhaust mods should make the most difference after you've done equal intake mods or you're just taking a laxative without eating anything imo. Okay that was dumb, but what are you gonna do? :P

EDIT:
To actually be useful here, you can buy the Mandrel bends from ERT and JCWhitney among other places. Then you buy the lengths of pipe you need for the straight sections. Have it welded together to match the bends of your OEM system and call it good. This is what I will be doing here pretty soon. (So many projects, so little time/money!) If you can weld and don't need to have SS piping, you could probably make your own for under $100 plus a muffler. :thumbsup