Since there is an exhaust thread pretty much every other day, I thought it would be good to make one for those looking to make their own custom exhaust. Many people tend to go this way because the aftermarket systems for our cars are becoming more and more difficult to find. Let's begin?
What size piping would be best for my GT/ST//GT4/etc?
This question really depends on your goals for the car, and what you do with it. My typical rule of thumb that has worked best for me, is 2.5" and below for N/A vehicles, and 3"-3.5" for turbo'd vehicles. The bigger the piping on an N/A, the more bottom end you will lose, however, you will gain better top end. Find your trade off point.
What about mufflers?
This is where it gets interesting. The muffler you use will determine how your car sounds. There are many different ones out there, and different types. You can have the traditional canisters, which you see mainly in the tuner scene, then there's the Magnaflow/Flowmaster type. Here are pictures showing each:
Canister:
Flowmaster/Magnaflow:
The difference in these mufflers comes from inside. Quality mufflers will have better construction and better quality inside baffling, which will bring out nice sound from your exhaust. Cheap mufflers like the ones you see on Ebay will use sound metallic and tacky. My personal recommendation if you choose to get a canister would be either the Megan Racing N1 replica ($70-$80 on Ebay), or the OBX B10 ($50-$60 on Ebay).
How do I get the piping?
Now here comes the fun part. After you've purchased your muffler and decided on your piping size, you get the piping itself. You can buy DIY exhaust kits online, which are fine if you know how to weld, but otherwise I recommend going to a local exhaust shop. From here, you can tell them what you're wanting out of your exhaust system, plus you can customize your muffler placement/angle, as well as the design of the piping, so that you can get the most straight piping possible for your setup. I paid $130 for 2.5" piping on my Supra, this included the piping itself, a resonator, and the labor to put everything on. You will want to get piping from the cat to the back of the car. Basically they cut the piping off from where it runs into your cat, and then weld on bigger piping. Many exhaust shops will NOT condone the removing of your cat, nor do I condone it. This brings problems with emissions, as well as state inspections, not to mention your car will sound like crap. I highly recommend getting a resonator added in with your piping to ensure a better sounding exhaust, you'll be glad you did it.
Here is my final result with my Supra:
I hope this will give you guys a better understanding on what to look for and get when wanting to get an exhaust system.
-Matt