Rear muffler delete, a good idea?

[19jacobob93]

I swapped my exhaust mounts the other day as some of them had perished clean in half causing the whole car to shudder at idle. In the process I broke a rusty weld on my rear muffler and it now rattles around like crazy, and has the typical blown exhaust sound!

Searching eBay, the cheapest option is to replace the rear section with a straight pipe without the muffler and I also like the idea of making it a bit louder as these are good sounding engines.

Would there be any downsides to doing this i.e. loss of fuel economy or torque?

Part is below. Original exhaust has a muffler between those two mount pins
http://www.ebay.com.au/itm/151030724850

 

[Olas]

torque is a function of cylinder-filling, so a different pipe right at the end won't make any difference imo (the cat and other silencers were the bottleneck before the straight pipe, and will be after..

fuel economy..well.. the engine still operastes the same but you put your foot down more often to hear the noise so your persobnal fuel economy goes down..

 

[eljefino]

So is there some sort of resonator in the middle?

I had a turbo Volvo with two mufflers, one in front of the axle and one rearwards. The whole mess was rotten. I cut them all off and put in a single $22 "Thrush" muffler. Didn't sound all that different; the turbo ate most of the noise anyway.

You should be able to sawzall that pipe and put a universal muffler in the middle if it drives you nuts.

 

[yvon_la]

you can,but I don't suggest it!

 

[earlyre]

to me the only problem that pops up could be the noise level, depending on local laws/inspection procedures. i know in the UK the exhaust has to be below a certain decibel level to pass...

We need more of those laws around here. too many kids @ the Auto-Diesel-High Performance Motorsports College here have either the big "[censored] can" mufflers on their 4cyl cars, or they have jacked up diesel trucks with twin 6 inch stacks coming up through the bed... leaving clouds of black smoke every chance they get...

 

[Olas]

There is no specific volume in the UK for an exhaust to comply with, the only rule we have is a yearly roadworthiness inspection.

In relation to the exhaust, thew wording is;

Requirements
Complete, secure, without serious leaks and silences effectively.


Test procedure

The exhaust system must be free from serious leaks or advanced corrosion. The entire system must be securely fixed to the vehicle as intended either by using exhaust mounts or the common rubber fitting mounts. The exhaust system must have the required number of silencers for your specific make and model of car. Your vehicle may fail the MOT due to noise levels if deemed to be excessive by the MOT inspector.



So, as you can see, the volume of the exhaust must not be 'excessive'.
The MOT tester who likes the sound of triple DCOE's will have a very different perception of 'excessive' as compared to the meek MOT tester who talks as quietly as a mouse and only listens to quiet classical music.
( It pays to be friends with your tester in this country

)

 

[IndyIan]

I took the muffler off the Neon for autocross a few times, and replaced it with a straight pipe to get the exit behind the bumper. Its really too loud for normal driving though. Eljefino's thrush muffler is a good idea at a bare minimum.

 

[JTK]

This depends on the specific make/model vehicle and the drivetrain it has.

Removing the rear muffler if pretty common on late model Subaru Imprezas. You get a little more boxer burble without it. Basically a slight sound increase is it. Some owners who did this mod with the CVT trans didn't like the drone noise, where 5spd owners reported little/no drone.

 

[dparm]

Performance impact will be negligible with a different muffler.

 

[bigjl]

Originally Posted By: JTK
This depends on the specific make/model vehicle and the drivetrain it has.

Removing the rear muffler if pretty common on late model Subaru Imprezas. You get a little more boxer burble without it. Basically a slight sound increase is it. Some owners who did this mod with the CVT trans didn't like the drone noise, where 5spd owners reported little/no drone.


Why?

Late models have equal length manifolds so no boxer burble unless you swap the manifolds back to unequal.

I have never seen or heard any Scooby with back box removed.

Cat removed yes and a full catback 3" stainless aftermarket exhaust.

But remove the rear box/muffler?

Can't see the point.

I put an aftermarket stainless backbox on my 04 Legacy and it sounded very muted, more character certainly but no boxer burble. And i had come straight from an 04 WRX with an Sti backbox.

 

[SteveSRT8]

Originally Posted By: dparm
Performance impact will be negligible with a different muffler.


This is the real answer. Expect extremely minor gains if any. Most every modern car has a fully optimized exhaust on it already, and most folks gain noise and that is all.

Always be especially careful of hatch backs and wagons as these drone like crazy!

 

[ARCOgraphite]

Even as a kid lookin for trouble this type of mod was too noisy for me after a day or too. My 401 nailhead buick sounded REALLY good with a single cheerybomb and full tailpipe - lost power over the classic corvair califronia turbo muffler.

 

[JTK]

Originally Posted By: bigjl


Why?

Late models have equal length manifolds so no boxer burble unless you swap the manifolds back to unequal.


I'm not sure how to tell, but I've seen owners post over at NASIOC and XV Crosstrek forums that the new FB20's have unequal length exhaust manifolds.

I think the main reason why some do it on the new Impreza hatchback and XV is because it's super easy to do. Just a flanged elbow is all that's needed to replace the rear muffler. Sedans have a totally different system.

 

[ARCOgraphite]

Originally Posted By: JTK
This depends on the specific make/model vehicle and the drivetrain it has.

Removing the rear muffler if pretty common on late model Subaru Imprezas. You get a little more boxer burble without it. Basically a slight sound increase is it. Some owners who did this mod with the CVT trans didn't like the drone noise, where 5spd owners reported little/no drone.


I don't understand the appeal This engine ( EJ) with a loud exhaust sound like a sixer with two bad plug wires - absolutely horrendous.

 

[JTK]

Originally Posted By: ARCOgraphite


I don't understand the appeal This engine ( EJ) with a loud exhaust sound like a sixer with two bad plug wires - absolutely horrendous.


I hear you ARCO. They do sound like a *miss* or a Cessna aircraft engine.

I'm not sure if the FB sounds any different from the EJ. It's the FB I'm referring to above. Like I say, I've seen claims made that they use the unequal exhaust runners. Dunno.

 

[19jacobob93]

The car has a resonator, a small muffler before the rear axel, and then the big one behind the axel which I will be removing, so it will still have a resonator and a small muffler at least I can get a full cat back system for a hundred bucks more but I don't want it too loud and end up sounding like too much of a redneck haha plus it would get annoying on long trips ands defeats the object of having a big comfy cruiser

There are no laws on sound over here judging by all the straight piped v8s everywhere, as long as it still has a cat it's legal.
And I'm not in the UK haha I moved to Aus nearly 2 years ago when I was 18, definitely wouldn't find someone my age driving a car of this size over there!

The reason I'm worried about losing too much back pressure is because I love the low down 'breathe on the pedal' torque of this engine and I know reducing back pressure shifts the torque curve up the rpm scale which I don't want.
As some have said nearly all the back pressure is created through the stock manifold and cat so I shouldn't lose too much

I'll give it a go anyway, for $65 I'll be happy if I get a nicer sound at least

Cheers guys

 

[19jacobob93]

Originally Posted By: bigjl
Originally Posted By: JTK
This depends on the specific make/model vehicle and the drivetrain it has.

Removing the rear muffler if pretty common on late model Subaru Imprezas. You get a little more boxer burble without it. Basically a slight sound increase is it. Some owners who did this mod with the CVT trans didn't like the drone noise, where 5spd owners reported little/no drone.


Why?

Late models have equal length manifolds so no boxer burble unless you swap the manifolds back to unequal.

I have never seen or heard any Scooby with back box removed.

Cat removed yes and a full catback 3" stainless aftermarket exhaust.

But remove the rear box/muffler?

Can't see the point.

I put an aftermarket stainless backbox on my 04 Legacy and it sounded very muted, more character certainly but no boxer burble. And i had come straight from an 04 WRX with an Sti backbox.



Interesting!
I've always wondered how imprezas managed to sound like they do with that burble, making such a small engine sound almost like a v8 or more accurately as someone said a 6 dropping a cylinder or two haha
I always thought it was just somehow a magical characteristic of a boxer but unequal manifolds makes perfect sense.

 

[JimPghPA]

Most likely, the second muffler is called a resonator, and if you value listening to music while you drive then you do not want to remove it. Without the resonator there will be a certain RPM range where the exhaust will be loud enough to interfere with listening to the stereo in your vehicle.

If you and all the other people who ride in that vehicle are hard of hearing and do not value listing to music while you drive, then it will not be a bad idea to remove the resonator.

 

[ARCOgraphite]

Originally Posted By: JTK
Originally Posted By: ARCOgraphite


I don't understand the appeal This engine ( EJ) with a loud exhaust sound like a sixer with two bad plug wires - absolutely horrendous.


I hear you ARCO. They do sound like a *miss* or a Cessna aircraft engine.

I'm not sure if the FB sounds any different from the EJ. It's the FB I'm referring to above. Like I say, I've seen claims made that they use the unequal exhaust runners. Dunno.
The FB exhaust is quite elaborate and changed from the EJ. Ill look for some pix ... IIRC its a tapered merge 4-into-1 unequal log.

 

[Mr_Incredible]

I've done this with about all my trucks. Whittle away as it rusts through. Doing it now on my '99 Super Duty. Plenty of room for a downturn on the end of a piece of pipe and air to take it away.

Not so much on my cars...