I have a 2000 A4 1.8t atw engine code and I have friends telling me to remove the cat nd just put a straight pipe in just woungering if it weill be ok would have to cut into the pipe for the o2 sensor just looking for less restriction probley when I do this I want to order a neuspeed exhaust with the down pipe just woundering if anyone has done this or knows somebody that has tried it.

Thanks

 

You have to consider the O2 sensors. The precat sensor is important for accurate readings being sent back to the ecu.

But why the extreme obsession with "less restriction"???
If you get the DP's and the Neuspeed, you will have much better flow.

 

I askedcon of the tech's here and they told me there was a way to re wire it to trick the system.

 

Yes, that's true, but still...

 

I justb thought less restriction on a turbo motor is better the less the restriction the more the power my buddy has a 3 gen rx7 he took of his cats had his car tuned with a stand alone fuel management he is looking at 330whp

 

Well you have a good idea, but there's a fine line between increased hp and loss of torque. As you increase flow (decrease restriction) you do increase some hp, but you lose torque also. Also, the increased hp is minimal (with this sort of modification) and it is found at high rpms. More importantly, increases in hp, due to increased exhaust flow, inversely affect torque - torque decreases. There is a mathematical formula that calculates the optimal point of compromise; it determines where any further increase in hp is minimal while the torque decreases will be significant enough to suggest that the net result will not be optimal.

I don't know this particular formula off hand, but I do know (as an example) it has been shown that anything over a 3 inch pipe system, after the exhaust manifold, compromises the hp and torque values. I am assuming (only) that removing the cats would increase flow beyond the optimal value. I may be wrong about this, but something tells me that cat removal causes the same undesirable effect. Automotive engineers have to contend with this issue while designing the exhaust system; I imagine that Audi engineers did their job well.

Remember, that with the increased flow, the increased hp will be found at the top end of the rpms, only. You will have to be constantly revving the engine over 5500 to reap the benefits of the additional hp.

 

If you did this, how would the car sound?

corey

 

Here's the formula... Horsepower = Torque + RPM / 5252* OR Torque = Horsepower + 5252* / RPM. I can't remember how to correct for elevation above sea level.
I've still got my cat, but I took the factory mufflers off. The 5252 is suppose to be the RPM where your torque and horsepower are equal, not sure what that should be
for a 1.8T.

 

i know this thread is quite dead, so we will call it lazarus. anyways...

its widely known that the best exhaust for any turbocharged car is no exhaust at all. the turbo and the turbo manifold produce enough backpressure for the engine so that no exhaust after the turbo is necessary. think about it logically. if there is backpressure in the exhuast system, what do you expect it to do? slow down the turbo, and force its way up into the engine where the backpressure is needed? i don't think so. all backpressure after the turbo is usless on a turbocharged car, on NA cars its a much different story(and a different one so...). what you will get from removing the cat and having the least restrictive exhaust possible is more HP across the entire power band, and the power band will start earlier as the turbo will want to spool instantly(no exhaust BP clogging it up)

so with no restrictions you will be better off, note that it will be louder and you will probibly shoot the occasional flame out your exhaust(not ff style, just a puff) due to the unburnt gas traveling through the exhaust and meeting with fresh air at the end(catalytic converters burn unburnt gas by slowing it down and heating it up). and if you have a fully atmospheric BOV expect to have after fires almost every time you build boost and blow it off.

im planning on running a full catless exhaust with glass pack resonator and 3inch in 3in out summit turbo muffler for my exhaust system, because im all about the powa baby! oh and im cheap


oh one more thing, the secondary o2 sensor(the one after the car) is really only there to monitor the usefullness of the cat, it tells the computer wether or not the cat is doing its job. what do you think that the computer uses the o2 readings after all the fuel has been burnt out of the exhaust gasses? lol not such. the secondary o2 sensor is useless, just eliminate it with a o2 sensor emulator (or some resistors possibly) if you wanna run catless.

 

I will let you know when i install my labree test pipe, if your thinking about a test pipe id remove the mid muffler before that if the new exhaust comes with one, you dont have to worry about DTCs that route.