Designing custom exhaust

[Ja2Mike]

I have a 92 Toyota Camry LE with the 4-cylinder engine and an automatic transmission, and have been wondering about a catback exhaust system.

Since this car is so old, no one makes them anymore, so i was wondering about building my own custom catback exhaust for it. Ive searched the forums and FAQ and havent quite been able to find the answers ive been looking for.

1. How difficult is building your own catback? I know how to weld, and can design and plan projects out somewhat well.

At first glance it seems like buying some tubes and connecting hardware, two mufflers, copying the stock design (except with bigger piping and less restriction, obviously) and welding it all together. Is there anything im overlooking or underestimating the difficulty of?

2. How much will it cost? Ive looked at some pipes and they seem pretty cheap, but i dont know about mufflers or hardware.

3. How long will it take? If i do all the designing before I actually take off my exhaust and start building, how many days should this take?

4. Is it worth it? What is the optimum exhaust diameter for the most power gain in a 4 cylinder for a daily driver (ive heard 2.25" or 2.5")? And will i gain enough power to make it worth the cost and effort?

[Brian R.]

For a muffler, you might consider using a 3rd gen Camry V6 muffler. I've heard they are less restrictive than yours.

I had a Midas shop build me a custom exhaust for an old Camaro I put headers on many years ago. For them, it was pretty trivial. Took them a couple of hours.

[jdmccright]

The old mantra "bigger is better" is only true up to a point with exhaust diameter. You want good, smooth exhaust flow. Too large and you lose the scavenging effects that the exhaust airflow velocity does to pull more fresh air into the cylinder to dilute residual exhaust gases. And too small causes back pressure...also bad for scavenging. What's the best size? Good question. Stock ID is 2", so upping to 2.25" or 2.5" isn't unresonable.

1. Welding is one part, so is fitting and pipe bending. And don't forget about the hangers too. You'll have to either cut them from the original or fab new ones...adjusting for the increased diameter. (it's always been a peeve of mine that the Camry exhaust hangs down from the undercarriage!)

2. The pipes can be cheap (steel to aluminized steel) or expensive (409 stainless). Also remember again the bolt-up flanges and hardware. The most expensive pieces will be the cat and the muffler. If I were just starting, I'd learn on the cheap stuff and use flanges to bolt up the cat & muffler. If you don't like it, you're not out alot of $$$ and your cat & muffler aren't trashed.

3. Length of time will probably depend on how quickly you can find the parts to fit your design. Higher dollar stuff may take longer to find & ship. IT'll also depend on how much custom fitting you'll have to do...lots of bends, welds, oopsies, can drag it out...remember you're learning at this, so the time factor is eventually well worth it in knowledge and experience.

4. An exhaust mod is probably one of the better ways to effectively increase HP...but we are talking a 4-cyl Camry here. Most of the gains will be in the higher revs, but it'll only be worth it if you like the feeling in the seat of your pants. I would hazard to say ~10HP for a well-designed, free flowing system. For a 5s-fe, that's about a 7% gain, but it will be noticeable. A good AM header would help, too, but those are also rare for the 5s-fe.

Here's a good, layman's description of exhaust design:
http://www.nsxprime.com/FAQ/Miscella...austtheory.htm

Good luck!

[jdmccright]

Update...I have seen a few OEM exhausts for sale on eBay. They were running in the $220 range including shipping. Thsis should at least give you a price floor to compare to when compiling your materials list for your custom job.

Let us know how it goes...I for one would be interested since my exhaust is looking pretty rusty too and and am thinking of going the same route.

[Ja2Mike]

For designing the exhaust, since im new to it, i was thinking of taking a weekend to get my car up in the air, blast those damn rusted bolts with some penetrating fluid and take everything behind the catalytic converter out.

with the exhaust out, i was going to dimension it and look at the way everything was mounted and attatched to eachother, then reinstall the exhaust and modify the original specs to handle 2.25 or 2.5 (maybe even 2.36" pipes, but since those are measured in metric usually i thought it might be hard to get an adapter for it).

with the new specs to work off of, i would order the piping i need, mounting hardward, and prebent pipes so i dont need to get them bent and just weld them together in series (from the flange where it would bolt to the cat to the mid muffler or silencer of w/e it is, then the mid muffler, then from where it would bolt to the mid muffler to the rear muffler, etc.) so it would go together more easily and with less chance for mistakes.

I probably wouldnt replace the catalytic converter. i think its been replaced before, and im fairly sure its in good shape either way. I was thinking of just getting a universal cherrybomb or magnaflow muffler, maybe an N1 (a friend of mine has it on his corolla and it sounds great, but how well does it really work?). Im looking for good flow but i would like nice sound (but not one thats obnoxiously loud, just a classy slightly understated roar)

although i doubt it, if anyone had an actual layout for the exhaust it would make my life a hell of a lot easier.

oh and thanks for that article jdmccright!