You won't necessarily need any fuel system upgrades, but it would be recommended to be on the safe side. While you're at it you may as well port your wastegate instead of waiting till later to do that. From the sound of your set up, you shouldn't really need an FCD or an AFC of any kind although it may be a good investment if you want to learn. If I had the money, I totally would have bought an SAFC of some sort so I can get the hang of tuning a bit. Might be something you want to look into, idk.

A wideband (Wideband O2 sensor) is a replacement sensor for your factory narrowband sensor. It measures afr, lambda and lots of other things. This is what you use when you're tuning a car messing with fuel maps and timing maps etc. Although there are lots of other ways of measuring this stuff, widebands are a beginner/intermediate's tool (from what I've gathered).

Your setup will be pretty conservative so I don't personally think you need that stuff but it could be a good idea, your call.

Most aftermarket downpipes cover the green and red areas you circled, so fabricating your own piece to go from the turbo to an aftermarket catalytic converter is definitely possible.

All this talk about fuel system upgrades and fuel controllers is getting ahead of yourself. Build your exhaust, and then see how the car reacts to it, you won’t know what your car will do until you build and run the exhaust. If you were buying a RB or some other full exhaust system then you could take the necessary steps to prevent things such as boost creep, but until you know what your car will do there is no need to spend a ton of money on AFC's and FCD's.

It might almost be less of a headache to buy a pre-bent downpipe. Rather than cutting up a bunch of mandrel bent pipe to get the correct angles I'm looking for. But I guess that depends on how much they cost, as that will determine the route I take. Like I said, not on a strict budget, but who doesn't like saving money? :)

As for the FCD and fuel controller, It would probably be wise to hold off. But I'm pretty sure at some point down the line, I'll want a fuel controller.

If and when fuel cut happens, does it damage the engine in any way? Or does it just feel/sound awful?

To answer the first part of that, yes the red and green circles are sold aftermarket as one piece called a downpipe.

As far as the Y-pipe, it is easiest to just buy one. You can many different variations at Jegs.

http://www.jegs.com/webapp/wcs/store...94913576&Nty=0

They don't seem to have one that does 2.5 to 2.5. My original thought was to cut a u-bend in half, then cut the half in half longways on both pieces, and weld them together. If that makes any sense....

you could do what i did, and just have an "emissions" exhaust.
and a "i wanna go fast and be loud" exhaust.

when u gotta go in for emissions or inspection, swap it out.

the cats will give back pressure building boost faster, but will have trouble breathing on the higher rpm ranges, and oppositely for an open exhaust.

exhaust only flow as good as its smallest diameter, so if u have a ''3inch" exhaust but have a restriction somewhere thats a 2inch. its only a 2inch exhaust.

i would def recommend boring out the wastegate!!! with a larger exhaust u will get
''boost creep''

you could get a fuel controller if you wanna make more power, but not a must.

there is no downfall of a FCD, itll save ur motor. it prevents the ecu from cutting fuel from the
front rotor, which will eventually damage the engine.

If you're putting on an aftermarket exhaust, you pretty much need an FCD. Or else you'll blow your motor. They aren't horribly expensive. Plus, I'd rather be safe than sorry.


I have a corksport downpipe + test pipe going to apex'i dual N1's. It's super loud plus I hit 13 psi sometimes. When I did emissions, I just put the stock cat + downpipe on + took the corksport stuff off. Took me about 45 mins to do.

You don't need to go from 2-1/2" to dual 2-1/2". A single 3" pipe will flow almost as much as dual 2-1/4" pipes will and actually is probably the size collector you should look to use. They've got those. If you want the 2-1/2" inlet it is going to have dual 2" outlets which is fine as dual 2" pipes flow as much as that single 2-1/2" do.

Ok, so I think I'm getting my head wrapped around this thing. So, I have two options.....

The first option:
-Buy RX7.com bonez cat and downpipe (2.5")
-Run 2.5" pipe to the "y"
-Run 2.25" pipe after the "y" to each muffler (Assuming I can go smaller without sacrificing power)
-Magnaflow stainless muffler on each side

The second option:
-Find a downpipe that is 3 inches
-Buy the RX7.com 3" cat
-Run 3" to the Y
-Run 2.5 to each magnaflow muffler

Are there chepaer options to any of the components listed above? Cats that are less than $250?

Will I EVER need 3" exhaust?

Any suggestions?

Nope.

I'll say it again. A single 2-1/2" pipe is equal in flow to dual 2" pipes. If you are running 2-1/2" up to the y-pipe, it won't matter if you run dual 2" or dual 22" pipes afterwards. The power will remain the same. I would however run the next pipe size larger in muffler though so if you have 2" pipes, run a 2-1/4" through muffler. If you run a 2-1/2" downpipe through a hi flow cat through an exhaust that separates into even dual 2" pipes through straight through mufflers, you will get lots more flow than stock.

Is 3" absolutely necessary? No. Then again the most powerful exhaust on a turbo car is no exhaust. Some people have claimed otherwise but they never retuned to take advantage of it. Realistically for what you are doing you probably don't need it. The stock wastegate will get into creep much faster. But, you'd make a little more power.

RotaryGod, I understand what you're getting at, and agree. I am still a little confused as to why I would use 2.25" mufflers instead of 2". Whats the benefit?

A 2" straight through muffler does not flow as much as a 2" pipe. A 2-1/4" straight through muffler does not flow as much as a straight 2-1/4" pipe and so forth and so on. You go up one size in muffler to take care of that.

Makes perfect sense. Thanks for clearing that up. So I'll need to add adapters to my shopping list :)

Thanks!

Wow, there is so much miss-information in this thread. If your exhaust is going to flow well, you will need a fuel cut defender or engine damage will occur from fuel cut. With an FCD you will want to get an accurate boost gauge so you know exactly how much boost the car is running. If it creeps up too high you will lean out and detonate. Porting the wastegate is a must and to do so does not require welding or a bigger door for the wastegate. The larger the port, the better off you will be. Just remember that backpressure is the enemy of the turbo. A larger exhaust will get quicker spool and more boost. Will you need a 3 inch exhaust now, probably not. Will you ever need a 3 inch exhaust, that depends on your goals for the car. Whoever said 2.5 inch is the mast you want to go is retarded and needs to do some reading on flow dynamics. With just the exhaust and even an intake, you will not need any fueling mods unless your boost levels go past 9-10psi. As for mufflers, I'm a big Borla fan but that's personal preference.

Tell that to mazdatrix, they recommend no larger than 2.5 inch exhaust. Also, if you yourself had a basic understanding of fluid dynamics (not flow dynamics), you'd know the importance of gas velocity and how that fits into the design of an exhaust system. I'd go into it, but I am sure you can read up on it on your own.

Here is a good arm chair explanation...

http://www.miata.net/garage/KnowYourCar/S4_Back.html

And a wiki article for further reading...

http://en.wikipedia.org/wiki/Fluid_dynamics

Good stuff right here!~

Although I no longer have a TII, I never had any issues with running just an FCD with a higher flowing exhaust. That car only had a downpipe and straight pipe in place of the cat although the mufflers were still stock. The car was noticably faster than stock but not a rocket by any means. It did have a boost gauge but also had a Profec-B boost controller. No larger injectors or fuel pump. The rest was all stock. The wastegate wasn't even ported. Worked fine. No blown engine.

Well I'm working on getting my hands on an FCD. I think I may already have one lined up, but I want to make sure I get one that clamps voltage, instead of reducing it by a percentage all the way through the boost level. That way the chance of a rich/lean mix are far less.

Does anyone know a brand of FCD that uses a volt clamp?

I do like Borla, but the cost is usually a bit much for my taste :/

Where does one go about installing an aftermarket boost gauge? Wish I could make the stock one work, nothing cooler than reading your boost in millimeters of mercury!

aftermarket boost gauge is pretty easy to install. And like already stated, the best exhaust is no exhaust, but not for a car your going to be driving everyday, and especially on the stock turbo.

my suggestion is to buy a cheap exhaust system and go from there....

http://cgi.ebay.com/ebaymotors/86-92...Q5fAccessories

I have learned its easier/cheaper to buy exhaust rather than make it yourself, unless you are using a lift and decent materials

We'res the fun in buying an exhaust??

The fun is in being able to install it in under an hour and be on the road enjoying it shortly after...

If performance and weight are your primary drivers then go Corksport.

If performance sound and looks are your primary drivers then go Racing Beat Rev-II. (But you will need to figure out a custom CC.)

Unfortunately none of that nonsense applies to turbo cars, necessarily. A turbo car simply wants the least amount of static pressure losses possible. In the upper RPM range on rotary turbo cars especially there is very little difference in temp and thus density of the compressible exhaust fluids. in a 2.5, 3 or even slightly larger exhaust. Quite simply, the bigger the better with an ever increasing diminishing returns effect.

Does anyone know the stock pipe diameter on the exhaust?