I’m installing my new exhaust system including Headers 60mm inner diameter at exit, down pipe 60mm inner diameter throughout, front pipe 80mm, and cat back 60mm

My question is… I’m I going to regret my front pipe being larger for performance reasons? For example, are there repercussion to the inner diameter expanding and shrinking again? Would a uniform set up perform better?

  • Welcome to Motor Vehicle Maintenance & Repair! What is the car in question? Year/make/model/engine? What type of header? Is it tube headers and what length (shorty/mid/full)? Commented Mar 14, 2023 at 12:45
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    Commented Mar 14, 2023 at 17:40

1 Answer 1


Headers should not be changed, unless you know what you are doing. Otherwise everything that goes from headers to rear wont have much affect on your performance.

Only way you would see decreased performance is, if you change exhaust diameter smaller than your header's is and if this new exhaust system is alot bigger than your OEM, then you can have issues with the Oxygen sensor, which affects perfomance and fuel consumption. This can be fixed with reprogramming ECU at the tuner.

Having midway 80mm isn't gonna do any harm, if its not near Oxygen Sensors.

Example: Your headers are 60mm, and as long you make your exhaust 60mm or above, it wont matter. Smaller than 60mm could lead to choking the engine.

Reason do not change headers: Headers are designed exacly the same way as your intake manifold. Manufacturers precisely calculate the headers lenght and diameter with using the parameters that the engine produces. Gas velocity, overlap, desired max torque @RPM, gas harmonics ect..

  • I understand what you’re saying about the headers… but I purchased what could be considered bolt-on replacement… however, I will be getting assistance with this issue due in large part to your response. Thanks for the advice.
    – MegaMark
    Commented Mar 26, 2023 at 22:35

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