my au2 is a 6 banger. I am using advanced headers, which is a south australian company, the guy that makes them spends hours and hours on dynos making sure they perform to their best, the guy selling me them and helping me fit them sells alot of others like pacemaker, but has alot of faith in these advanced and reckons that they are the way to go... he has fitted them on monaros, heaps of SS commodores and XR's...
The extractors are mild steel because a few fitters recommended that they wouldnt use the Stainless them selves as it increases engine bay heat. They said that the mild steel extractors are one of the last things to rust out as its so hot in there that little condensation happens.
From the cat back i am going stainless steel, 2.5" piping mendral bent (which means it doesnt change thicknesses on bends in case ya didnt no). I have been told that anything over 2.5 on a 6 is an over kill. Mendral bent is definately the way to go if you can get it as the pipes arent constantly changing sizes and dont have sharp bends, this allows a smother air flow.
For the cat i am using a high flow cat made by car sound. These are the people that own magnaflow. They spend alot of time designing them so they dont have any sharp edges and have good prices.
For the muffler i am using Genie. A pretty big name. Its a pretty small muffler so it should screch! if it gets too loud i mite have to stick in another small muffler. I am thinking probably a megaflow muffler, because i have been helping to fit them on alot of cars this week, and am impressed with them compared to most.
Really though you have to do alot of talking to people, ask to see other peoples cars up on the hoist to see what sort of job they do! its not just how pretty they are! See how well they clean up there pipes on other cars before they use them, even little bits on weld and metal are restrictions and created distorted sounds.
any good, honest company should be happy to let you see other cars as they are doing them. Not just when they are finished because anyone can polish a pipe and make it look pretty, its whats inside that counts! Also make sure that you get a warranty! if its stainless it should be at least 10 years.
Take your time though and make sure you are happy that the company will do a good job.
If i have forgoten anything hear or if you wanna know anything else just ask!
AU2 S-pack Owner: Silhouette Black, XR6 Wheels, Tickford Sunroof, C2R rear bar, Checker Plate Floor Mats, Chrome Door Sills, Blue Backlite Dash, Blue Painted Brake Callipers, Advanced Extractors, Magnaflow High Flow Cat, 2.5" Stainless Steel Mandrel Bent Custom Exhaust, Genie Muffler. Sony Explode 50w x 4 deck, Kenwood 140w speakers (front and rear), Boss 1200 watt Amplifier, 12" Orion Sub in custom box. More To Come!!