I am putting a 2.5 inch system in and am looking at options as to where to run the pipe apart from the factory place to avoid as.many bends to aid ease of installation reduce cost and increase flow. Can anyome who has done custom piping show me pics of your plumbing? Also undecided in mild steel or stainless.

Depends on how long you want to keep your ride. If only a few years and on a budget, then it's more cost effective to go mild steel.
Going stainless will negate any cost savings. Keep in mind that you will have to relocate your hangers if you don't want to use the original piping locations so that would cost you even more time and money!

If you are keeping your ride N/A, you are not going to see any HP increase by relocating the exhaust and trying to make it physically straighter.

Mitsubishi did a test on the ralliart magna back in the day where they replaced the exhaust from the cat back as a straight through with no resonators or muffler and it didn't make any discernable difference to the power or torque figures.

The TJ models and onwards had very good flowing exhaust systems standard anyway. Installing a VRX/Ralliart style free flow rear muffler alone will give you 5kw or so power increase and for FWD magnas this is the cheapest & best bang for your buck performance upgrade.
To complete the package, you can install a set of HM Perry headers and Y pipe, however this will be dearer (approx $500-600) and won't net you as much power gain as the rear muffler. But it would bring your exhaust system up to magna ralliart spec.
This combination will give you max flow and HP increase from your exhaust.

Any other exhaust mod is purely aesthetics and or potentialy worse performance and more noise.

Several members have been through the gauntlet of spending literally thousands of $$$ on various exhaust configurations only to revert back to a ralliart style set up in the end.

i have hurricane extractors, a lukey centre and a lukey rear to go in. have some damged pipe so am unable to bolt on new rear until pipe is replaced. all parts waiting to be installed. also high flow cat. all my parts are 2.5 in piping. is this close enough to the standard pipe size? also it is the pipe from my rear muffler that is rusted out at the end could i clean up the rust and weld new 2.5 inch pipe on is the size diff close enough? and i have been told the factory piping is mandrel bent however when i look under the pipe that goes over the rear axle appears to be however the 90 degree bends after cat seem more crushed and to me appear to be press bent.

If you are running only 1 lukey resonator and a high flow cat, then expect the sound to be raspy (if that's your thing). Otherwise you have all the components you need to maximise flow and pick up extra power. No need to change anything else to the system. ;)
BTW, stock cat already flows well so it's doubtful that a hi-flow cat will net you much more if any power. but from what I've read on these forums, user experience seems divided on this.

i will be prepared to add another resonator i am not happy with the sound. i have seen some magnas have multiple resonators stnadard and some only 1 what is the difference? mine only has one. alright well will leave the piping stardard for now mayb change it to stainless wen cash is a little better.

Most TJ's have 2 resonators. My previous '02 magna exec had 2. My TJ AWD has one tiny (4") resonator that is easy to miss and a larger 12" secondary just infront of the rear muffler. 2 resonators are used to minimise rasp and exhaust boominess in magnas.

I'm pretty sure that all TJ sedans from '01 (not sure about wagons) scored 2.5"mandrel bent systems from the cat back. Both my TJs did anyway. So ì can only talk from personal experience although other members have echoed similar.

mine is 00 TJ has the larege resontor behind the cat only and appears to be not mandrel bent pipe as there is a big difference to the diameter and you can tell there is a section on the inner edge of the curve that comes back out after the bend. i am not the most knowledgeble on mandrel bends but from what i have seen on mandrel bends these do no look the same.

Yeah sounds like pre '01 models had the 2.25" and press bent pipes. All I know is that later TJs had around 5kw incease over earier one's so undoubtedly, the revised exhaust size and mandrel bends had something to do with this.

No most j series had 1 resonator as did a lot of the h series. Mostly in the h and j series the 3.0 has the 2 resonators oddly enough

Hi flow cats are a waste of money, best setup on a std motor is the stock pipe work with a VRX .. Sports rear can. Hm rip is $830 but as you have hurricanes no need to replace them

i want to do the exhaust to also allow for better flow if/wen i go go down theroad ofmore power. definately would just a matter of whether or not i can afford the mods. if i went a 380 motor still stock piping good enough??

Yes, whatever suits the 3.5l will be fine for the 3.8l as well.

Bigger than 2.5" is only of use if you are going down the route of forced induction (turbocharging). Otherwise 2.5" mandrel bent system is plenty for high hp N/A motors. I've also decided to go the 3.8ltr motor route when it comes time for engine mods down the track. On a side note, I'm pretty sure that 2.5" freeflow is fine even for supercharged applications, although other members with S/C magnas can verify this.

just got a piece for my exhaust and realised i stuffed up. i was puerchasing what i thought was the right part to use for a centre and realised it is a 6" round. now it is a high flow lukey see here (http://www.ebay.com.au/itm/330671927368?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649#ht_500wt_1182) so the performance side of things will be great however it is too big obviously. what i wanted to know is how big is the standard centre and will this fit?

If you are refering to the resonator then it is 4" round body with 2.5" inlet/outlet. 6" body would be too big with the positioning of the stock exhaust. To make a 6" body fit you would most likely have to drop the exhaust 2" to accommodate which I wouldn't recommend as that affects ground clearance. Better off to exchange for correct item.