Did a muffler swap, total drop in MPG’s, driving mellow - TundraTalk.net - Toyota Tundra Discussion Forum

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post #1 of 8 (permalink) Old 04-04-2019, 03:47 PM Thread Starter
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Did a muffler swap, total drop in MPG’s, driving mellow

Hello. I got a great deal on a Spintech muffler. It is 2.5”/dual in a s 3” single out. If you are familiar with the muffler, it has 8 “coils” in it. I love to Do a few full throttle on ramp runs a few times a week. I also will do some dorky hyper-mileage-ing on fwy trips. My mpg’s are lower than they have ever been. With just a Hypertech, I have got 17-19 on some fwy trips (factory 255 tires). Now it is low 14’s.

Initially I was flooring it a lil’ more often to near the noise, but not anymore.

I disconnected the battery for a reset too. Still the same.

Has this happened to others?

2015 SR5, Crew Max, 4x4, 5.7, 4.30's, factory spray-in liner, white w/black interior, Hellwig rear bar, Hypertech, Bilstein 5100’s, middle setting.
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post #2 of 8 (permalink) Old 04-04-2019, 05:10 PM
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Maybe they sent you the GM or Dodge Ram version of the muffler

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post #3 of 8 (permalink) Old 04-06-2019, 02:32 PM
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Engines need back pressure to operate properly as your example clearly demonstrates. Still surprised at how many people think that the engineers at the various automotive manufacturers are stupid and some guy operating out of a small shop can provide a part that will dramatically improve performance in some way. All they do is lighten your wallet.
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post #4 of 8 (permalink) Old 04-06-2019, 07:40 PM
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Still surprised at how many people....[do stupid shit and then complain about the result]....
Why are you still surprised?
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post #5 of 8 (permalink) Old 04-06-2019, 08:09 PM
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post #6 of 8 (permalink) Old 04-07-2019, 07:42 AM
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Originally Posted by Youngfrankenstein View Post
Hello. I got a great deal on a Spintech muffler. It is 2.5”/dual in a s 3” single out. If you are familiar with the muffler, it has 8 “coils” in it. I love to Do a few full throttle on ramp runs a few times a week. I also will do some dorky hyper-mileage-ing on fwy trips. My mpg’s are lower than they have ever been. With just a Hypertech, I have got 17-19 on some fwy trips (factory 255 tires). Now it is low 14’s.

Initially I was flooring it a lil’ more often to near the noise, but not anymore.

I disconnected the battery for a reset too. Still the same.

Has this happened to others?
According to our resident exhaust expert Keith Carty, your system's 3 inch tailpipe is your issue. Call him at 1-760-877-4234 and tell him what you have. He'll explain what Toyota had in mind with the stock tailpipe size and give you some options.
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post #7 of 8 (permalink) Old 04-11-2019, 07:16 PM
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I did a muffler swap on a 2015 5.7L crewmax, all stock. I changed to a Magnaflow 12588 (which is a very quiet version) 2.5" dual in, 3" out because I wanted a little better exhaust note. I disconnected the battery to weld it all together. I went from 16.5-17 mpg to 14 immediately. After a while (6 months) the mileage is back up to about 15.5-16. I think the ECM may reset all of the variables and it takes a while of easy driving to get the mileage back up. Not sure this is true, but I have had to disconnect the battery a couple times and I get a big drop in mileage each time that seems to recover after a few months of driving.

Also, I had a terrible drone sound at 50-65 mph which I fixed by cutting off the tailpipe right after it goes over the axle and turns to the passenger side. Essentially, I cut off 21" of pipe. Drone fixed. There is a formula I posted somewhere in here to figure out how much to cut off, but if you get a drone like I did, 21" is the magic number for the Tundra.

Love the sound now and the mileage is back to normal so we are all good.
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post #8 of 8 (permalink) Old 04-13-2019, 03:03 PM Thread Starter
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Originally Posted by Mikecol View Post
I did a muffler swap on a 2015 5.7L crewmax, all stock. I changed to a Magnaflow 12588 (which is a very quiet version) 2.5" dual in, 3" out because I wanted a little better exhaust note. I disconnected the battery to weld it all together. I went from 16.5-17 mpg to 14 immediately. After a while (6 months) the mileage is back up to about 15.5-16. I think the ECM may reset all of the variables and it takes a while of easy driving to get the mileage back up. Not sure this is true, but I have had to disconnect the battery a couple times and I get a big drop in mileage each time that seems to recover after a few months of driving.

Also, I had a terrible drone sound at 50-65 mph which I fixed by cutting off the tailpipe right after it goes over the axle and turns to the passenger side. Essentially, I cut off 21" of pipe. Drone fixed. There is a formula I posted somewhere in here to figure out how much to cut off, but if you get a drone like I did, 21" is the magic number for the Tundra.

Love the sound now and the mileage is back to normal so we are all good.
Thanx Mikecol. Good info. Just what I did. Got a good deal on a muffler. Kept the stock tail pipe. It might be slowly improving since I initially posted.
Thanx!

2015 SR5, Crew Max, 4x4, 5.7, 4.30's, factory spray-in liner, white w/black interior, Hellwig rear bar, Hypertech, Bilstein 5100’s, middle setting.
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