jcaldwell

Ok, basically I want to "dump" my FD's exhaust. Just have the main cat and then nothing. I want to do this because I think it would look alot better, granted it dosen't look horrible with my Greddy PE, and it sounds great, but I would rather not the 4" tip, or anythign for that matter.

Really my only major concern is running too lean. My mods other than the reliability ones are Bonez Dp + cat combo, and the cat back. With that I am boosting to about a max of .8~.85 bar. Would taking the cat back off put my engine at risk? Would it make a difference if I swithced back to the stock cat and took the cat back off? Oh and are there and O2 sensors in the catback, I could see that causing a problem. Thanks.

TwinTriangles

Thats the dumbest thing Ive ever heard...
Have you ever heard a rotary with no exhaust ?!

Narfle

iTrader: (16)

look better as in have a big hole on the right hand side of your bumper where an exhaust is supposed to go? youre already running lean. you should not be boosting over 0.7 bar. unless you have an upgraded ecu. it will sound horrible. yeah, replacin gyour high flow with the stock cat might keep you from leaning out. but it wont save you from lookign stupid and sounding even worse. 02 sensors reside as close to the exuast ports as possible w/o melting = no there are no 02 sensors in your catback. you go ahead and do what you want.

JTurtonRX_7

I sense a "OMG my I popped my motor" thread in the near future.

Think man, do some reading and learn what you are getting into.

When you remove the catback + mid-cat that will give you far less backpressure which in makes your turbos produce more boost than your ECU can compensate for and that = boom its rebuild time

Gadd

Do you realy mean NOTHING not even a pipe to the rear of the car??

I sence a "OMG, my car is on fire" thead.

jeremyb

I ran open DP for a bit... its a liiiiiiiittle loud...(i hope you saw the sarcasm in that ). Do you have an aftermarket ecu? If you're stock... you're probably already running lean and on the edge running .85 boost. What do you mean you wanna dump the exhaust system? As in run open DP? I don't really think anyone can REALLY help you until you clear your question up.

MazdaSpeed93

He must of found out that that was a stupid idea, he hasn't even written back on his own thread. He must not want anymore put downs, Its his car and he can do what he wants but he should REALLY look at your guys' thoughts and opinions, they MIGHT be right IMO.LOL

jcaldwell

Not sure what wasn't clear about that but my exhaust path would go something like dp then main cat then possibly some pipe over to near the passenger side.

Would it not look any different than the other side?

Or I could have gone to sleep alittle early.

And their thoughts would be right except, oh wait, all six of you have the reading comprehension of a 3rd grader.(Except Barban I went back and read it again and he managed to atleast answer most of my questions)

How much of a difference would an performance cat back make. I know it still creates back pressure but say it cuts the back pressure from the main cat back in half from stock. Then removing it would make me boost like what maybe .5 bar higher to .85~.9 bar or about 12.5#s. I don't see why this wouldn't work using the 3 mod rule... counting the no cat back as 2 mods and the dp as one.

TwinTriangles

There are so many reasons why this is an extremely retarded idea, how dont you see this ?
Your car is going to sound like absolute ****, some of that exhaust is going to creep inside the car while you sit at stop lights and its going to make you even dumber, its going to look stupid with nothing coming out of the exhaust cutout in the back & its going to over boost & run like ****

broken93

Well, aside from the obvious engine management issues, I can attest that my twin turbos through only one muffler (a large magnaflow in the center) is absolutely loud as ****, so I run two mufflers, the mag and a PFS cat back in the rear... you have no idea just how loud an unmuffled rotary engine is... when I was testing with no exhaust, the police came to my house...

cletus

I wouldn't completely rely on the "3 mod rule" as an exact science. I wouldn't just add up different things and say "well, that only counts as one" and so forth. That can be a really expensive assumption. I would definitely verify if you are running lean somehow (of course I'm paranoid and put in an A/F gauge and I only have a cat-back).

As for the exhaust, my catback is just a 2.5" (or 3, I forget) pipe, no muffler. It isn't very loud honestly (my rotary shop commented on how they thought it would be a lot louder). It's basically all I can get away with though and stay in SS class for autocross. But because of that and the fact that I live in an area with emissions testing, I still have the stock pre-cat and cat. I am sure that helps quiet it down some. It's quieter than the riced out civics riding around by a good bit.

And I agree with others, you do need to get that exaust out from under the car somehow before terminating it.

Narfle

iTrader: (16)

You have to understand that the exhaust is touch and go concerning the 3 mod rule. The three mod rule is not a rule at all, just a crappy standard. When you free up youre exhaust you create more boost than you can control. If you do not already have a boost controller or modified ecu you really must get one. Boosting anyhting over 10psi on the stock ecu is driving your engine straight into the ground, at a very fast pace. Even the 10psi debate is under heat as i have heard it is cfm, not psi, that matters. I have no idea how the cfm/psi relationship works but i am absolutely certain that you need a new ecu! Take your time! Do it right! SAVE YOUR ENGINE! they are not cheap...

jcaldwell

Yea I understand the whole relationship between freeing up intake/exhaust resulting in more boost and more boost on stock ecu being bad. Also I really don't see how running anything over 10 psi is driving my engine straight into the ground at a fast pace, there is no way mazda set the a/f ratio that close to detination, the engines have run rich form the factory, therefore a few mods being ok. Thats like saying having an aftermarket ecu with a slightly aggressive tune is completely killing your engine. And FWIW I would get a PFC but ofcourse that voids the Mazda warranty (Lets not get into the I'm a dumbass for getting the engine done at a dealership).

And this "exhaust cut out" every one talks about is almost non-existant, go look, it is like a 1/2" of black plastic cut off, other than that it looks JUST like the other side.

cletus

EGTs are too high to dump it under the car constantly, plus it's just not good to breathe.

As far as the cfm/psi thing, I'll see if I can explain it (poorly). It's the amount of air in the engine that matters, the amount of O2 molecules for the combustion process. At 10 psi, in theory, you could be flowing 5cfm or 500 cfm through a system, all depends on the system. Obviously there is a lot more O2 molecules around with the higher cfm (more air mass). Opening up the intake and exhaust will allow more air (O2) through without ever increasing the boost. Hopefully that will get the point across. And don't forget the FD uses a MAP sensor, just checking incoming pressure, not actual air volume, and the stock maps were created assuming a stock flow for a set pressure.

As far as what Mazda did for tuning, they probably didn't take into account people modding their cars very much. In the end, they are most likely worried about their money and meeting gas milage and emission standards. They don't have to do warranty work if they can just say adding stuff on caused the engine to blow, so that would save them money anyway.

There is a lot of experience on this board. It would be wise to listen to some of these people. They have already been the guinea pigs. But then again, it's your money, do whatever you want, although I wouldn't recommend it. You seem to have your mind made up.

hemlock

I see you've got a few of the all too common "what the hell is wrong with you" replies. Not very helpful.

Cletus has done a good job trying to explain the downfall of increase boost and increased airflow, without upgrading the ECU. More boost isn't bad - but a lean airflow mixture is. In layman's terms it boils down to the fact that if you're going to add more air, you need to add more fuel. If you don't the mixture gets leaner. Sounds simple doesn't it?

You are correct that Mazda did design the engines in the 3rd gen somewhat on the rich side. Just to make sure that even on an extremely cold day at sea level with maybe an injector failure at WOT you don't bring them a warranty claim for new engine. They cover their ***. Can you run leaner than stock? Certainly. Where is the limit to how lean? Your car - your rules. Personally I am against your set of modifications and increased boost on the stock ECU for the same reasons that Cletus mentioned. I also know that for extended periods of WOT the other components in your system (i.e. bypass valve, etc.) will not be able to keep up and you are going to see boost creep. Making your mixture that much leaner. But again it's your car. Do what you like. To avoid a potential catastrophe I would highly recommend the installation of a A/F Gauge if you haven't already done so. If it looks too lean, stop driving until you fix it. Or pay the piper.

I do have one question for you though. You mentioned that an aftermarket ECU would void your warranty. How does increased boost and no exhaust NOT void the warranty already?

jcaldwell

Heh, don't ask me about the warranty but the car was taken to them with a bad motor with the exhaust mods on it and the new engine was put in with all the exhaust mods on it. They did specifically say though that any ecu other that stock would void it. And I do understand the relationship between running lean, opening the air flow, and blowing engines. That was basically why I started this thread, to see how much the cat back restricts the flow.
Also I have no problem boosting my car to 11.5 psi on the stock ecu, that is 15% more air, if it can even be measured like that, and I am willing to bet that that falls within the margin of error set by the factory. And for what its worth I'll be leaving the exhaust the way it is. Thanks.

jcaldwell

ghey