Custom Exhaust Build
 

I've decided for economical purposes, and for the fun of it, I'll be building my own exhaust. I'll be running three inch all the way back, and was hoping for suggestions from you guys for the cat and muffler combo. A friend that owned an FB had used magnaflow mufflers that were around 70$, and they sounded decent even on his 12a. With mine being a turbo though, are there any special considerations to be made? Do I need to worry about melting stuff on the cat or muffler? Do I need to buy "rotary" specific stuff?

I should also mention that I prefer nice, conservative exhaust notes. This build is sort of a "sleeper" you could say. And it needs to be emissions legal.

Go 3" down pipe to a RX7.com cat, then 2.5" back to the muffler. the 2.5 will keep boost kreep down (you will still get some) for a muffler just get a style you like but don't go and buy some knock off crap, it'll just fall apart.

take lots of pics :) if you need advice or help you can always come down to the shop and shoot the shit

Crash, thanks for the advice, sounds good :) I sort of forgot about the boost creep thing.

Gurew, may take you up on that, being as you're local. Where you located?

What size is the stock downpipe?

we should be moved into the shop sometime this week, if so it will be mcclintock and rio salado in tempe, right across the street from tempe market place

I couldn't comment much on keeping it to legal standards, I don't know what the smog laws are like in AZ, but i figured they are similar to CA. The set up I posted up should keep it pretty close to legal depending on the muffler you chose.

Oh one other thing, I've learned this from trial and error. When building something from scrach make sure you do loads of planing, take your time, and have pride in your work. GL and take pics!

So why did mazda use so many Cats in the stock system, if one cat would do the job?? Seems counter-productive....

Port your wastegate!

I read that I can do that. Would there be any reason not to just port the waste gate and run three inch? Any benefits to running 2.5 inch?

its about flow..more cats gets you more flow through the exhaust vs a single cat

If you port the wastegate you will need a bigger gate door(which requires welding), and still you will have boost creep, it does not cure it, to rid yourself of boost creep you need a good electronic boost controller and an external gate.

If you take a look at the RB exhausts you'll see that they don't use huge piping and yet they are one of the BEST exhausts for a lightly modded turbo rotary.

Bigger isn't always better.

Dual or single exit?

If your going twins you can attempt the set up im thinking of unless your thinking of a budget custom exhaust build.

3' down pipe, with WB02 bung at the end.
3' high flow cat with air pipe inlet
Multi layer resonator welded into the midpipe
into 2 Apexi World Sport2 Mufflers to keep the noise down while retaining power across the board.

With this you can bring up your boost levels, and see some power gains. Also keeping the emissions active down stream. And with 3 levels of noise reduction from the cat/resonator/muffler you can retain your sleeper status. Be sure you have a FCD ready in place.

If they are the magnaflow stainless glasspacks, those are supposedly bullet proof. I actually have a set on order right now.

Linky...

http://www.summitracing.com/parts/MPE-10415/

There is a youtube video with an s4 and a few 12A's with those on, and they sound great. Nice thing is, since it is stainless, and has a wire mesh support, they won't blow out. Stainless tubing and outer shell as well.

On the same note, I do caution you that 3" may bit a bit too much. Mazdatrix recommend not exceeding 2.5 inches for even racing applications.

Ok, so based on suggestions, I'll stick with 2.5".

I do plan on doing dual exhaust. However, I figured with the turbo, cat, and dual mufflers, I wouldn't need a resonator. (I suppose I can always add one later)

The Apexi mufflers, are they pricey? I'm not on a strict budget per-se, but I'd be happier spending less money :)

Gurew, I'm confused, how do more cats increase flow??

Does the air-pump inlet have to go "in" the cat? can it be in the pipe before the cat? I figured if I couldn't find a cat with an air pump inlet, I could weld the old one on the new one. Or are air inlets pretty common on most cats?

The RX7.com cat seems like it would work. It's a big chunk of change though, but I suppose it's the price to be paid to stay legal....

I'm pretty sure I want to stick with the magnaflow mufflers. But like I said, I REALLY don't want to be heard from miles away. Some people may enjoy that, I don't. I don't need to draw anymore attention from patrol cars than a bright red tuner car already does. And I just prefer/love the sound of a really conservative exhaust.

No. The "pre-cat" was a low temp catalyst that would reduce emissions during cold start until the main catalytic converter would "light off" and begin to do the main work of reducing the emissions once everything got up to temperature.

http://rightofmiddle.files.wordpress...03_468x572.jpg

So if i had all these cats in my exhaust, id have a free flowing exhaust?! Wow thats news to me!

You NEED to get a cat that has an air inlet pipe. This will help you pass emissions. It'll be hard as hell if you try to pass emissions without one.

You'll need a fuel cut defender. What this will do is trick the ECU into thinking that your boost won't go over stock (when it will creep up from your exhaust) whenever it goes over 8.8 psi I believe the motor will cut fuel to the rear rotor. Then pop goes the motor.

Another thing that is good to have is some sort of fuel controller also. With your wideband you can then tune it to a decent air/fuel ratio.

I have an FCD and an apexi SAFC neo for sale if you want either. PM me if you're interested.

Also post pics when you're done!

Forgive my ignorance incubus, but you'll have to clarify a few things if you can for me :)

On this fuel controller, you mentioned having a wideband? Not sure what you mean...

Are there any downsides to having an FCD?

Also, will a fuel controller be necessary at this point? What are the benefits to having one? Will it make more headaches than it's worth for me?

One cat won't do the job, not while the engine is warming up. Mazda has to meet actual emissions standards, unlike manufacturers of aftermarket cats.

I'd use a 3" downpipe to the y-pipe and then split it to dual 2-1/4" or dual 2-1/2" pipes and then proceed through dual Dynomax 2-1/2" superturbo mufflers. It would be very quiet and would flow more than your engine will ever require.

I hope you guys are ready for some crude drawings and odd questions. I'm trying to get my parts list together, and get an over-all cost drawn up.

http://i615.photobucket.com/albums/t.../s5exhaust.jpg

Can I replace the red and green circled areas with one down-pipe? Or do I need to buy a pipe that will bolt to the turbo, then buy or build something that will replace the green pipe?

And how do I re-create the "y" pipe in yellow in 2.5", since I want dual exhaust?