BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > catless dp vs. catless exhaust

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      08-09-2009, 10:34 PM   #1
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catless dp vs. catless exhaust

hi foks -

I am trying to move on to my next mod (already have JB+ and Helix FMIC). Would like to do both DP's and exhaust at some point in the near future.

Trying to understand the benefits of going catless in either or both the DP's and exhaust. Its intriguing since the price difference is 300 per for catted. But I am not sure of the OBD (and sound) ramifications of going catless on both. At the same time tryiing to understand power dymamics of catless dp w/ catted exhuast vs catted dp w/ catless exhaust.

While I am at it. WTF is an O2 sim? Does it mimic the o2 sensors somehow to fake the presence of a cat in a catless system?

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      08-09-2009, 11:07 PM   #2
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From this URL: http://www.o2sensorsimulator.com/

All performance enthusiasts are looking for any possible way to increase the power and efficiency of their engine. Most have added a cold air intake with a K&N type air filter to allow maximum airflow into the engine for starters. The engine itself and the Engine Control Module (ECM) are then modified in thousands of different ways for horsepower gains.

The modified engine now produces a larger amount of exhaust gases then the stock exhaust system was designed to handle so it's time for another upgrade. Aftermarket headers, larger pipes, high flow catalytic converters and high flow mufflers are all employed to allow these gases to exit as freely as possible reducing the effort of the engine to expel them.

All cars and light trucks made since January 1, 1996 have an On Board Diagnostic system (OBDII) that monitors all of the sensors in the car. When one of the sensors sends a signal that is not within the manufacturers specifications the OBDII system logs an error message. Why is this important? If you have removed your catalytic converter or even installed a high flow cat you probably already know why: an error from the secondary oxygen sensor will illuminate the Check Engine Light (CEL) and you will not be able to pass emissions.

Catalytic converters of often removed because they are the single most restrictive part of the exhaust system. With the increased flow comes another increase: pollution. The oxygen sensor will sense the high content of carbon monoxide and hydrocarbons and signal the OBDII system. This will illuminate the CEL and can cause the car to run on limp mode actually reducing performance. To prevent the error caused by the increased emissions an Oxygen Sensor Simulator can be installed.

The function of the Oxygen Sensor Simulator or O2 Sim is to mimic the signal of an O2 sensor sensing the proper levels of emissions. The O2 sim has an output signal wire that will replace the O2 sensor's signal wire to the engine control module. Now, with the cat removed, the check engine light will be off and no error message will be logged.

It is advised to use one of these devices for off road use only. They are NOT street legal. The oxygen sensor simulator may allow you to pass today's emission inspection because the test merely reads the OBDII log to see if there are any emission related error codes.
Also, try asking in this subforum: http://www.e90post.com/forums/forumdisplay.php?f=58
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