Muffler Delete Question - Toyota GR86, 86, FR-S and Subaru BRZ Forum & Owners Community

dutchman1 · 02-02-2018, 04:50 AM

I have a MRT muffler delete, dual exit. It's quite damaged from getting run over (long story). All the damage is on the right side of the exhaust, it's pinched flat.

I can simply cut the exhaust just to the right of the left side hangers and cap it, turning it into a single exit (as marked in picture). Question is would this hurt the performance of the exhaust at all? It looks to me like you'd still have plenty of flow, albeit the dead end would create a tiny bit of a bottleneck. I'm running an otherwise stock car with no tune (street class autocrosser so that's all I'm allowed). I was planning to switch to a single exit anyway.

I don't know a whole lot about how the exact shape of an exhaust impacts flow and sound. Thanks for any opinions.

Williampreza · 02-02-2018, 08:03 AM

It would not hurt performance by any significant amount, although you would be creating a sort of Helmholtz resonator out of the stub from the cutoff part. That will change the way the exhaust sounds, but that's going to change anyway.

You could perhaps do some calculations and tune it to cancel out any drone frequency that's bugging you. Just need to figure the volume of the dead end cylinder you're making and weld a cap on it.

My 2 cents...

dutchman1 · 02-02-2018, 08:16 AM

Quote:

Originally Posted by Williampreza

It would not hurt performance by any significant amount, although you would be creating a sort of Helmholtz resonator out of the stub from the cutoff part. That will change the way the exhaust sounds, but that's going to change anyway.

You could perhaps do some calculations and tune it to cancel out any drone frequency that's bugging you. Just need to figure the volume of the dead end cylinder you're making and weld a cap on it.

My 2 cents...

Thanks, the Helmholtz resonator effect did cross my mind. But I have no idea on how to approach calculating the frequency the resonator would cancel out. So unless someone with a little more engineering knowledge can chime in, I'd be guessing as to the size lol. If I don't get that figured out I'd just cut it as short as possible to save weight.

JazzleSAURUS · 02-02-2018, 11:32 AM

Get an exhaust shop to make a capped tube with a slip joint u bolt to hold it in place. You can slide it in and out and adjust until you're happy with it, then have them weld the cap on to ensure it doesn't leak in the future.

Clipdat · 02-02-2018, 01:22 PM

I don't know how this brand designed theirs, but the WORKS version of this design actually has a smaller internal exit hole for the driver's side exhaust pipe. Presumably in order to balance out the sound.

I would visually check with a flashlight to determine that both exit pipes are fully opened.

x808drifter · 02-02-2018, 04:11 PM

Enjoy.
[ame="https://www.youtube.com/watch?v=azPKIjxmmdU"]Exhaust Header Bash! Testing Power Loss From Dents - Engine Masters Ep. 4 - YouTube[/ame]

FRSBRZGT86FAN · 02-02-2018, 10:40 PM

Quote:

Originally Posted by Clipdat

I don't know how this brand designed theirs, but the WORKS version of this design actually has a smaller internal exit hole for the driver's side exhaust pipe. Presumably in order to balance out the sound.

I would visually check with a flashlight to determine that both exit pipes are fully opened.

Quote:

Originally Posted by dutchman1

I have a MRT muffler delete, dual exit. It's quite damaged from getting run over (long story). All the damage is on the right side of the exhaust, it's pinched flat.

I can simply cut the exhaust just to the right of the left side hangers and cap it, turning it into a single exit (as marked in picture). Question is would this hurt the performance of the exhaust at all? It looks to me like you'd still have plenty of flow, albeit the dead end would create a tiny bit of a bottleneck. I'm running an otherwise stock car with no tune (street class autocrosser so that's all I'm allowed). I was planning to switch to a single exit anyway.

I don't know a whole lot about how the exact shape of an exhaust impacts flow and sound. Thanks for any opinions.

Best bet is to weld in a vibrant resonator, or switching to an axleback that has a muffler. I had the berk muffler delete and it seems completely like yours, and I remember someone welding in a resonator in with good results.

humfrz · 02-02-2018, 10:44 PM

Quote:

Originally Posted by dutchman1

I have a MRT muffler delete, dual exit. It's quite damaged from getting run over (long story). All the damage is on the right side of the exhaust, it's pinched flat.

I can simply cut the exhaust just to the right of the left side hangers and cap it, turning it into a single exit (as marked in picture). Question is would this hurt the performance of the exhaust at all? It looks to me like you'd still have plenty of flow, albeit the dead end would create a tiny bit of a bottleneck. I'm running an otherwise stock car with no tune (street class autocrosser so that's all I'm allowed). I was planning to switch to a single exit anyway.

I don't know a whole lot about how the exact shape of an exhaust impacts flow and sound. Thanks for any opinions.

Oh, dutchman1, you're on the verge of overthinking this. I'd suggest you just cut it off and cap it about where your line is.

The exhaust will find it's way out ....... it only has a 2 liter pump.

humfrz

ApexEight · 02-02-2018, 11:21 PM

It would be fine, but I would personally just buy a J2 Engineering muffler delete off eBay. They're cheap and mine's held up well.

dutchman1 · 02-03-2018, 12:35 AM

Quote:

Originally Posted by humfrz

Oh, dutchman1, you're on the verge of overthinking this. I'd suggest you just cut it off and cap it about where your line is.

The exhaust will find it's way out ....... it only has a 2 liter pump.

humfrz

Haha I think you're right. This somehow turned from "is it okay to cap this" to "lets engineer a catback."

Thanks for the input everybody.

And to address the concern of another poster, the driver's side pipe has no restriction in it so that shouldn't be an issue.

I'll let everyone know how it turns out.

guybo · 02-03-2018, 08:14 AM

If the design is like other similar muffler deletes, the driver's side is much smaller than the passenger side. Most of the exhaust actually goes out the passenger side (I had a Berk and have a Works). So I think it may be a restriction and cause high RPM power issues. Measure the most restricted part of that exhaust and if you can, have it bored out or drilled out as much as possible so it's no smaller than 2.25"

Like Williampreza said, you could make a helmholtz out of it. If it was me, I think I'd lop off the pipe right there and leave it open or even better, drop $150 for a berk single exit

02-02-2018, 04:50 AM	#1
dutchman1 Senior Member Join Date: Nov 2016 Drives: 2017 86 6-Speed Location: Seattle Posts: 138 Thanks: 35 Thanked 74 Times in 36 Posts Mentioned: 0 Post(s) Tagged: 0 Thread(s)	Muffler Delete Question I have a MRT muffler delete, dual exit. It's quite damaged from getting run over (long story). All the damage is on the right side of the exhaust, it's pinched flat. I can simply cut the exhaust just to the right of the left side hangers and cap it, turning it into a single exit (as marked in picture). Question is would this hurt the performance of the exhaust at all? It looks to me like you'd still have plenty of flow, albeit the dead end would create a tiny bit of a bottleneck. I'm running an otherwise stock car with no tune (street class autocrosser so that's all I'm allowed). I was planning to switch to a single exit anyway. I don't know a whole lot about how the exact shape of an exhaust impacts flow and sound. Thanks for any opinions. __________________ 2017 86 set up for CS STX autocross Last edited by dutchman1; 02-02-2018 at 05:16 AM.

02-02-2018, 11:32 AM	#4
JazzleSAURUS Senior Member Join Date: May 2015 Drives: 15 BRZ LTD, 05 FXT Location: Western MA Posts: 1,032 Thanks: 561 Thanked 560 Times in 353 Posts Mentioned: 10 Post(s) Tagged: 0 Thread(s)	Get an exhaust shop to make a capped tube with a slip joint u bolt to hold it in place. You can slide it in and out and adjust until you're happy with it, then have them weld the cap on to ensure it doesn't leak in the future. __________________ SOLD: 2015 WRB BRZ Limited ('02 WRX BBS, S-04's, Stoptech Sport pads, MXP SP, AVO drop in filter, Mishimoto Intake tube, decatted header, OFT 93 Stage 2 EL Tune, Kartboy rear shifter bushing, Whiteline transmission and subframe lockout bushings, ST Coilovers, SPC Camber bolts w/smaller crash bolt, SPC LCA's & SPC Toe Arm bushings, Red TOMs, TRD Wing.)

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02-02-2018, 08:03 AM	#2
Williampreza Senior Member Join Date: Feb 2017 Drives: 2017 Ice Silver BRZ Limited Location: East TN, USA Posts: 147 Thanks: 235 Thanked 90 Times in 46 Posts Mentioned: 0 Post(s) Tagged: 0 Thread(s)	It would not hurt performance by any significant amount, although you would be creating a sort of Helmholtz resonator out of the stub from the cutoff part. That will change the way the exhaust sounds, but that's going to change anyway. You could perhaps do some calculations and tune it to cancel out any drone frequency that's bugging you. Just need to figure the volume of the dead end cylinder you're making and weld a cap on it. My 2 cents...

02-02-2018, 04:11 PM	#6
x808drifter LMGTFY Join Date: Mar 2016 Drives: 13 FRS, 91 Miata Location: Lava Town, HI Posts: 2,776 Thanks: 5,561 Thanked 3,650 Times in 1,625 Posts Mentioned: 15 Post(s) Tagged: 0 Thread(s)	Enjoy. [ame="https://www.youtube.com/watch?v=azPKIjxmmdU"]Exhaust Header Bash! Testing Power Loss From Dents - Engine Masters Ep. 4 - YouTube[/ame]

02-02-2018, 11:21 PM	#9
ApexEight Senior Member Join Date: Apr 2017 Drives: 2014 Subaru BRZ Limited 6MT SSM Location: Atlanta, GA, USA Posts: 293 Thanks: 195 Thanked 71 Times in 55 Posts Mentioned: 3 Post(s) Tagged: 0 Thread(s)	It would be fine, but I would personally just buy a J2 Engineering muffler delete off eBay. They're cheap and mine's held up well.

02-03-2018, 08:14 AM	#11
guybo Huge E85 fan! Join Date: May 2016 Drives: 2016 Scion FRS Location: Tampa, FL, USA Posts: 1,850 Thanks: 539 Thanked 1,010 Times in 605 Posts Mentioned: 32 Post(s) Tagged: 0 Thread(s)	If the design is like other similar muffler deletes, the driver's side is much smaller than the passenger side. Most of the exhaust actually goes out the passenger side (I had a Berk and have a Works). So I think it may be a restriction and cause high RPM power issues. Measure the most restricted part of that exhaust and if you can, have it bored out or drilled out as much as possible so it's no smaller than 2.25" Like Williampreza said, you could make a helmholtz out of it. If it was me, I think I'd lop off the pipe right there and leave it open or even better, drop $150 for a berk single exit

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