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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Powertrain and Drivetrain Discussions > N54 Turbo Engine / Drivetrain / Exhaust Modifications - 335i > any one thought of gutting downpipes?



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      05-05-2007, 04:16 PM   #23
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Its not a big deal in some states.

+1
in some states in the USA it is NOT illegal to run no cats. so yes you are right
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      05-05-2007, 04:20 PM   #24
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If the stock units are not double walled then they are extremely large and aftermarket units may not provide any benefits. The bends are not too bad either...
regardles of bends which is not the reason of gaining power or losing...its the fact that there is a cat right off the turbo which is robbing the turbo. running no cats on this car is going to be a HUGE performance gain. so yes there will be PLENTY of benefit with running no cats.

the bends have nothing to do with it. Take out the cats and try to even see a peak of light from the other end....its imposible!!! its a wall that is robbing power from the car.
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      05-05-2007, 05:48 PM   #25
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+1
in some states in the USA it is NOT illegal to run no cats. so yes you are right
It is against federal law to remove or alter the emissions related equipment on vehicles used on the roadways. While some states may not require emissions related equipment they cannot circumvent the federal laws.
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      05-05-2007, 05:54 PM   #26
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regardles of bends which is not the reason of gaining power or losing...its the fact that there is a cat right off the turbo which is robbing the turbo. running no cats on this car is going to be a HUGE performance gain. so yes there will be PLENTY of benefit with running no cats.

the bends have nothing to do with it. Take out the cats and try to even see a peak of light from the other end....its imposible!!! its a wall that is robbing power from the car.
Agreed that the major contributor to releasing power in the exhaust is by removing the catalytic converter. However, many people will be required but local regulations or, for other reasons such as ethics, desire to retain the cats and so all aspect need to be explored.

BTW, it is interesting to see the number of Audi people here now. I just sold my 388WHP/416WTQ B5 S4 (with the main cats intact ) to make the move to the 335i.
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      05-05-2007, 07:40 PM   #27
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How do they manage the change in AFRs? That would be the biggest issue I'd think, though I'm not aware where the O2 sensors are located in the exhaust track but I'll assume they're after the pre-cats.

Also, DP is the standard abbreviation for downpipe. As is CB for cat-back, MP for mid-pipe (any open pipe replacing the main cat) etc...

And I'm going to ignore comments on the emissions thing else I'll go on a tirade against all the conservatives in the world.
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      05-05-2007, 07:47 PM   #28
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How do they manage the change in AFRs? That would be the biggest issue I'd think, though I'm not aware where the O2 sensors are located in the exhaust track but I'll assume they're after the pre-cats.

Also, DP is the standard abbreviation for downpipe. As is CB for cat-back, MP for mid-pipe (any open pipe replacing the main cat) etc...

And I'm going to ignore comments on the emissions thing else I'll go on a tirade against all the conservatives in the world.
The factory sensors, shown below (8 and 9), are wide band units and used directly in closed and open loop fuel control.



I am not sure what emissions controls requirements and conservatism have to do with one another. In fact, this seems to be a bi-lateral matter.
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