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California98Civic · 02-25-2012, 02:37 PM

Anyone who reads this site regularly knows that periodically someone posts a question about what effect swapping their stock muffler for an aftermarket one will have on their fuel economy. Others ask about exhaust pipes or headers.

Some ask whether removing the muffler entirely will help fuel economy or power. Sometimes people post items for sale online that make unlikely-sounding FE claims. Some ask broadly what effects a mod might have.

The consensus answer tends to be that aftermarket muffler claims for fuel economy are usually bogus, exaggerated, or unproven. Changing the muffler size or the pipe size will have little benefit for fuel economy unless coupled with a general exhaust tune (including calculated pipe sizes) to maximize benefits. There are exceptions. One exception, noted in comment #4 below, is the effect of exhaust mods on a turbo diesel engine (corroborated here and here). Another exception is that shields and wraps of the exhaust header are effective in reducing engine bay temperatures and some have argued improved high-rpm power and/or fuel economy may result if the velocity of exhaust gasses increases as a result of preserved heat (though the FE claim is unproven, see here and here).

A well-known chart on pipe sizes often is suggested as an aid to judging the proper pipe diameter. A caution about this chart is that it always refers to the MAX horsepower a car might produce. MAX hp is reached at very high RPMs (such as 6000rpms). Unless you are modding for racing, you are not likely to be at the max hp for more than perhaps 1% of the car's life. The calculator will not help much in planning for FE gains or everyday driving.

I hope to use this thread to consolidate the best information into one place, through links such as those above and any comments you offer below. Please stay on topic: mufflers, exhaust pipes, exhaust headers, pipe diameter, and how to use them to benefit fuel economy or emissions or (preferably) both. I'll periodically edit this post to include links to other threads or products suggested below.

My own muffler is on its last legs, rusting out and patched around the tailpipe. In researching the claims through this site, I decided to post this thread.

Thanks for reading this long post.

[EDIT: I have installed a Thrush Turbo muffler because it is lighter and flatter than the stock Bosal and will help me with a rear diffuser or belly-pan install. It will not benefit FE or power. I weighed both: 9lbs for the Thrush and pipes and 18lbs for the OEM Bosal. I think it is quieter than the Bosal, but it required welding so it was not cheaper. The Bosal would have bolted on.]

02-25-2012, 02:37 PM	#1 (permalink)
California98Civic Cyborg ECU Join Date: Mar 2011 Location: Coastal Southern California Posts: 6,299 Black and Green - '98 Honda Civic DX Coupe Team Honda 90 day: 66.42 mpg (US) Black and Red - '00 Nashbar Custom built eBike 90 day: 3671.43 mpg (US) Thanks: 2,373 Thanked 2,172 Times in 1,469 Posts	the muffler and exhaust mod thread Anyone who reads this site regularly knows that periodically someone posts a question about what effect swapping their stock muffler for an aftermarket one will have on their fuel economy. Others ask about exhaust pipes or headers. Some ask whether removing the muffler entirely will help fuel economy or power. Sometimes people post items for sale online that make unlikely-sounding FE claims. Some ask broadly what effects a mod might have. The consensus answer tends to be that aftermarket muffler claims for fuel economy are usually bogus, exaggerated, or unproven. Changing the muffler size or the pipe size will have little benefit for fuel economy unless coupled with a general exhaust tune (including calculated pipe sizes) to maximize benefits. There are exceptions. One exception, noted in comment #4 below, is the effect of exhaust mods on a turbo diesel engine (corroborated here and here). Another exception is that shields and wraps of the exhaust header are effective in reducing engine bay temperatures and some have argued improved high-rpm power and/or fuel economy may result if the velocity of exhaust gasses increases as a result of preserved heat (though the FE claim is unproven, see here and here). A well-known chart on pipe sizes often is suggested as an aid to judging the proper pipe diameter. A caution about this chart is that it always refers to the MAX horsepower a car might produce. MAX hp is reached at very high RPMs (such as 6000rpms). Unless you are modding for racing, you are not likely to be at the max hp for more than perhaps 1% of the car's life. The calculator will not help much in planning for FE gains or everyday driving. I hope to use this thread to consolidate the best information into one place, through links such as those above and any comments you offer below. Please stay on topic: mufflers, exhaust pipes, exhaust headers, pipe diameter, and how to use them to benefit fuel economy or emissions or (preferably) both. I'll periodically edit this post to include links to other threads or products suggested below. My own muffler is on its last legs, rusting out and patched around the tailpipe. In researching the claims through this site, I decided to post this thread. Thanks for reading this long post. [EDIT: I have installed a Thrush Turbo muffler because it is lighter and flatter than the stock Bosal and will help me with a rear diffuser or belly-pan install. It will not benefit FE or power. I weighed both: 9lbs for the Thrush and pipes and 18lbs for the OEM Bosal. I think it is quieter than the Bosal, but it required welding so it was not cheaper. The Bosal would have bolted on.] __________________ See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread. Last edited by California98Civic; 12-09-2012 at 03:02 PM..