A larger exhaust will help conduct more heat way from the engine quicker and make it possible to run higher fuel levels. I'm not sure, on it's own that it will contribute much power but I'm pretty sure that it won't cost power.

Eventually, I'm going to be running a larger exhaust system on my car with an Aeroturbine diesel rated muffler.

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-Evan


Benz Fleet:
1968 UNIMOG 404.114
1998 E300
2008 E63


Non-Benz Fleet:
1992 Aerostar
1993 MR2
2000 F250