SI Sedan Stock Exhaust Measurements

[2020MSMcivicSI]

Just posting this as information for everyone... I could not find this information anywhere.

All these measurements are outside diameter (OD), and were done with a caliper on a 2020 civic SI sedan. The exhaust was on the car and the car was on ramps so I didn't include any partial mm (I rounded) because its hard to verify exactly square with pipes while laying under it. I did my best to accurately measure everything after the front pipe. With that said, the first measurement is the least accurate. I did not want to fully drop the plastic and it was difficult to get the caliper in the narrow channel while bending down the plastic. Also, after the resonator, the SI exhaust STARTS to get oval and continues to get MORE oval the further you go back until the input to the mufflers.

The honda parts sites list the SI sedan exhaust as part number 18307-TBF-A03 and it says it applies for all years 2017-2020 so I am going to assume the measurements here apply to all 10th gen SI sedans. (Probably applies to coupe as well but who really knows...)

Here are the measurements from front to back:
1) Immediately after front pipe flange: 52-53mm
2) 1-2" down pipe after a weld: 61mm
3) Input to resonator: 61mm
4) Output of resonator: 60mm
---- START OVAL SECTION ----
5) After bend 4-5" after resonator: 66x57mm
6) Pipe at end of last heat shield before Y split: 71x49mm
7) After weld at start of Y split: 83x59mm
---- END OVAL SECTION ----
8) Input to muffler: 60mm
9) Output of muffler: 57mm
10) Input to HDMI tip: 57mm

All the oval pipe is more wide than tall as installed on the vehicle. I will eventually drop the exhaust when I replace it and will update this if anything was wrong.

Hope it helps.

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[das borgen]

weight?

 

[2020MSMcivicSI]

weight?

Exhaust was never removed from the car so about 2900 lbs... lol

 

[Hondanickx]

Exhaust was never removed from the car so about 2900 lbs... lol

Great! Thanks for measuring this! The SI exhaust is as big as the Type-r exhaust .Only the rear section is different .Type r goes to 2x 2" the SI is actually bigger .
So this is also why PRL said the stock exhaust isn't a restriction .(They tested the Oem Si exhaust )
This makes a lot more sence now....Actually suprised the SI exhaust is this big .

 

[2020MSMcivicSI]

Great! Thanks for measuring this! The SI exhaust is as big as the Type-r exhaust .Only the rear section is different .Type r goes to 2x 2" the SI is actually bigger .
So this is also why PRL said the stock exhaust isn't a restriction .(They tested the Oem Si exhaust )
This makes a lot more sence now....Actually suprised the SI exhaust is this big .

Yeah, I was really surprised how soon it goes oval and how large the pipe is after the split... There has to be a reason why honda decided to basically double the volume in the rear section, but that is beyond me.

For the PRL thing tho... they proved that dumping to atmosphere after front pipe is the pretty much the same as stock exhaust HP and torque. This does not mean that every exhaust adds nothing. If properly designed, an exhaust can actually increase exhaust velocity (over straight pipe or dump to atmosphere) and therefore add HP. But I doubt there are significant gains to be had until you get high up the modification ladder.

I'm really starting to think that reusing the stock pipe with other components could work out without being a restriction, but I don't know if I really want to hack up the stock exhaust.... decision, decisions

 

[Hondanickx]

I can confirm these measurements of the oem FK8 type-R exhaust :

1) Immediately after front pipe flange: 54mm
2) 1-2" down pipe after a weld: 61mm
3) Input to resonator: 61mm
4) Output of resonator: 60mm
---- START OVAL SECTION ----
5) After bend 4-5" after resonator: 66x57mm
6) Pipe at end of last heat shield before Y split: 70x50mm
7) After weld at start of Y split: 83x60mm
---- END OVAL SECTION ----
8) Input to muffler: 51mm
9) Output of muffler: 51mm

The only difference is in the rear mufflers ,but i think the type R mufflers are straight true free flowing ones in 2" and the SI mufflers make a loop inside .So maybe that's why they are larger 2.25".

 

[2020MSMcivicSI]

I can confirm these measurements of the oem FK8 type-R exhaust :

1) Immediately after front pipe flange: 54mm
2) 1-2" down pipe after a weld: 61mm
3) Input to resonator: 61mm
4) Output of resonator: 60mm
---- START OVAL SECTION ----
5) After bend 4-5" after resonator: 66x57mm
6) Pipe at end of last heat shield before Y split: 70x50mm
7) After weld at start of Y split: 83x60mm
---- END OVAL SECTION ----
8) Input to muffler: 51mm
9) Output of muffler: 51mm

The only difference is in the rear mufflers ,but i think the type R mufflers are straight true free flowing ones in 2" and the SI mufflers make a loop inside .So maybe that's why they are larger 2.25".

Wow... so they are the same (except for the rear section with the mufflers). The largest difference between our measurements was at the beginning and that was by far my least accurate measurement. Everything else was within 1 mm and could easily be manufacturing tolerances or measurement inaccuracy.

I have never seen a cut out of the SI mufflers, but I would bet they are chambered like the hatchback sport. My guess is they basically flow into a dead towards the outside of the car and when there's a large enough pressure differential, exit out the muffler in the same direction they entered.

 

[AVR]

Wow... so they are the same (except for the rear section with the mufflers). The largest difference between our measurements was at the beginning and that was by far my least accurate measurement. Everything else was within 1 mm and could easily be manufacturing tolerances or measurement inaccuracy.

I have never seen a cut out of the SI mufflers, but I would bet they are chambered like the hatchback sport. My guess is they basically flow into a dead towards the outside of the car and when there's a large enough pressure differential, exit out the muffler in the same direction they entered.

So Basically if you just bore out the catalytic converter and have a ktuner you are good. ?

 

[2020MSMcivicSI]

So Basically if you just bore out the catalytic converter and have a ktuner you are good. ?

I would recommend buying a downpipe over destroying the stock cat, but that's up to you. Also would recommend a front pipe, the stock SI front pipe is smaller than the rear section (60 mm). But beware, the stock exhaust with a catless downpipe sounds weird to put it nicely. You will be very buzzy.

If I had time to test stuff and make repeated trips to an exhaust shop, I would have tried just downpipe and front pipe with a vibrant resonator put in front of the stock resonator and leave everything else stock. Then if that wasn't sounding good, replace the stock muffler section... basically keep changing just 1 thing until I liked it.

 

[arpypat]

I would recommend buying a downpipe over destroying the stock cat, but that's up to you. Also would recommend a front pipe, the stock SI front pipe is smaller than the rear section (60 mm). But beware, the stock exhaust with a catless downpipe sounds weird to put it nicely. You will be very buzzy.

If I had time to test stuff and make repeated trips to an exhaust shop, I would have tried just downpipe and front pipe with a vibrant resonator put in front of the stock resonator and leave everything else stock. Then if that wasn't sounding good, replace the stock muffler section... basically keep changing just 1 thing until I liked it.

I recently added a 3" RV6 catted DP/FP combo to my otherwise stock Si catback. I have some drone and I don't like it. Very little rasp, so I can live with that. Not sure if it's my Perrin RMM inserts either, so I'm getting rid of those and seeing if that makes a difference.

I'm also debating if I should reinstall my OEM DP/FP or get a Vibrant resonator put inline somewhere after the front pipe. Do you recommend the Vibrant 1141? And where would be the best place to install it?

• Between the front pipe and OEM resonator; or
• Between the OEM resonator and OEM mufflers

 

[2020MSMcivicSI]

I recently added a 3" RV6 catted DP/FP combo to my otherwise stock Si catback. I have some drone and I don't like it. Very little rasp, so I can live with that. Not sure if it's my Perrin RMM inserts either, so I'm getting rid of those and seeing if that makes a difference.

I'm also debating if I should reinstall my OEM DP/FP or get a Vibrant resonator put inline somewhere after the front pipe. Do you recommend the Vibrant 1141? And where would be the best place to install it?

• Between the front pipe and OEM resonator; or
• Between the OEM resonator and OEM mufflers

I have the Perrin RMM inserts as well.... the problem is that the stock exhaust sucks in the sound department.

The only easy place to put the Vibrant resonator is after the front pipe but before the stock resonator. There is already a place with heat shields there (type-r has an additional resonator in this location). I am currently running the vibrant 1141 resonator and the vibrant 1110 muffler (but also have a Borla muffler too). I think the combo is a nice "mellow" tone.

 

[arpypat]

I have the Perrin RMM inserts as well.... the problem is that the stock exhaust sucks in the sound department.

The only easy place to put the Vibrant resonator is after the front pipe but before the stock resonator. There is already a place with heat shields there (type-r has an additional resonator in this location). I am currently running the vibrant 1141 resonator and the vibrant 1110 muffler (but also have a Borla muffler too). I think the combo is a nice "mellow" tone.

Thanks for the response! I'd hate to get rid of the nice performance DP/FP, so I might add the Vibrant 1141 resonator in that area you mentioned.

I only have some mild drone around 1800-2200 RPM, so it's not terrible so long as I'm not lugging the engine. Just have to downshift more often and I don't want to catch myself lugging anyways. Maybe the drone can serve as reminder for that LOL

 

[Vincent@27WON]

This might be helpful for some.

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