FasTT 225

and would this most likely turn out to be a complete disaster? just tryin to save some money, i know a pretty good exhaust guy

also, how do u get everything to run smoothly after removing the cats? i did a search and read that you will need a chip w/ fault code erase but will the car run fine after that? thanx guys

John P. (TT 225)

had one made.

FasTT 225

with some nice sounding mufflers i suppose it could work out beautifully, but it also makes me really nervous

RoninTT

key word there is *might*, since the computer uses the pre and post cat O2 sensors to determine whether you are running too lean/rich or not. I think I would want to keep that functionality since a bad MAF caused mine to run too lean and if the car hadn't had the O2 sensors there it wouldn't have been able to compensate very well.

I would assume, without cats, the car will think you're running too rich ALL the time and cut the fuel back, causing an extremely lean condition.

I wouldn't risk it for the minimal HP and turbo response you *might* get.

Ex-TT

<center><img src="http://pictureposter.audiworld.com/27876/customexhaust.jpg"></center><p>

SwifTT

in the making just this past summer.. sorry kinda dark, but you get the idea

<img src="http://pictureposter.audiworld.com/7670/dcp_2014.jpg">

<img src="http://pictureposter.audiworld.com/7670/dcp_2010.jpg">

<img src="http://pictureposter.audiworld.com/7670/dcp_2009.jpg">

sTTanford

the second O2 sensor (O2S2) is usually only used while the cat is lighting up, or warming up. during this period, the ECU is running on a closed-loop feedback system. once stable operating temperature is reached (determined by O2 levels on the second sensor) the ECU enters open-loop control, and no longer actively uses O2S2 to determine fueling and timing.

now you'll still get a CEL if you don't have a cat, whether or not you use the second O2 sensor or not.

also, a 2.5" DP and losing the cat boosted my car from 150 ft-lbs to 200, altho the turbo couldn't hold the torque curve up high. getting rid of the cat will result in a noticeable difference usually, but with tinya$$ K03s or K04s, i dont think it is worth it.

here is my custom exhaust:
<img src="http://images.fotki.com/v12/photos/4/42448/156750/IMG_0840-vi.jpg">

mcgilla

very nicely done...what muffler did you choose?

RoninTT

Correct me if I'm wrong, but here is how I've understood it...

It still checks O2S1 after warmup, otherwise, it wouldn't know for sure if it was running lean or rich. At least this was true in my case. It's open loop in that it bases fuel delivery on MAF readings(the open loop target) without 'past value' compensation(ie. O2 readings), but can be interrupted if the O2 senses the A/F ratio is drifting too far (the closed loop/error feedback part). Such was the case with my persistent CEL that turned out to be a bad MAF sensor.

I think about this stuff waaay too much.

sTTanford

but my memory fails me.

it might be open-loop (IE always running rich) until the cat warms up, then closed loop based on MAF and O2S1.

anyway, sounds like u get my drift =)

i also recall (i think) an OBDII compliant car switching feedback methods during transients (ie when u left off the gas, stomp on the gas of cruising, etc). this was on a Ford F150 or F250.