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Nissan Repair/02 sensor


Just thought of another ? after researching catalytic converters and seeing a straight test pipe that is supposed to increase HP by 12-15% which has me wondering if leaving things the way they are with the converter removed is going to end up giving me the same mileage as if I replace it and the sensors?

Hi Clem -

Not sure if I understand your question, but I will try to target my answer.

The CAT does cause a certain amount of back pressure in the exhaust which can rob both gas mileage and power. I have seen many with so much back pressure that the CAT actually got red hot because it disintegrated inside and clogged the system.

Replacing it with a straight pipe is a common practice, however one has to worry about local emission laws which vary from state to state. It also causes the check engine light to come on because the O2 sensors cannot detect a change in the emissions before and after the CAT.

I think you are asking if a new CAT is the same as a straight pipe as far as performance? The answer is no. A straight pipe will always allow exhaust gases to escape faster consequently resulting in more power and better fuel mileage, but as mentioned it might be against the local emissions laws in your state.

Hope this helps -


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Calvin Iwashita


All general car repairs for all models of vehicles, except technicals (overhauls) on A/C systems and transmissions.


16 years as a car mechanic from 1974 to 1990, and still repair cars on the side.


High School and college graduate

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