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Modded Stock Muffler: Derestrict and Remove baffle insert restrictor 11> RMZ - Tutorial, How to with pics

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Hi Folks

I searched a heap of keywords through these forums about removing the insert which was added to the stock mufflers from 2011 onward. Brought to light by MXA mag tests which state:

“The RM-Z250 is very quiet (and no matter what anyone tells you, when you make a bike quiet by reducing the core size, it loses throttle response). Suzuki managed to keep the same size end cap from the 2010 muffler (in order to save money), but decreased the size of the muffler core with a mod that is pure backyard engineering in its simplicity. Instead of making a new core size, which would require a new end cap, they slip-fit a section of smaller core into the old core to bring the size down.” 

 

I found plenty of people asking about removing the reducer, but no answers to our questions. 

 

As background to this adventure. I recently bought a 2012 RMZ250 with 10 hours on it, and with a full stainless Yoshi RS4 system on it. I prefer to run it with the lean connector, and the spark arrestor baffle inserted. I find it gives the best punch in the mid range, so I can pop wheelies up and down my paddock :-) And on the track I'm not fast enough to make use of a screaming top end. 

However Yoshi's own dyno chart showed barely any improvement in performance over the stock system. Though this chart doesn’t specify if it was before the reducer was added, or after. (10 or 11 model?) It says both (top right corner of image below). Lets assume it was the '10 model and that's why they are running so similarly. Though if this dyno was the restricted '11 model it would serve Yoshi's purposes better, and perhaps it is? Maybe the unrestricted stock gives better chart figures than the Yoshi. Who knows? Remember, ride impressions may rave aboutbetter poweformance, but if it's louder we all know how increased noise may make some individuals feel like they've got more power, though they may not. Pity the information is not available (that I've found). 
Dyno Chart: 

Yoshimura_Suzuki_RMZ250_RS4_Chart_zps082

 

Also, dyno testing the 250 RMZ versus after installation of the 270 kit showed a great improvement in hp using the stock exhaust system. The Author also wrote that aftermarket pipes made stuff all difference to his findings. Again it wasn’t specified what year model, but as it was written in 2013 we’ll assume it was baffled. Read this thread here:
http://www.thumpertalk.com/topic/1004620-dyno-rmz250-stk-vs-270/?hl=%2Bcylinder%20%2Bworks#!Ha5M3

 

My theory, if the Yoshi does stuff all, and the 270 kit provides it’s substantial improvements when used with the stock pipe, then perhaps I can just run the much lighter stock pipe, and sell the RS-4 to finance some better mods. (270 kit, pcv, cams, meshless filter, skid plate, rad braces etc - actually I've already ordered the 270 kit...)

So I pulled apart my muffler last night and this is what I found. 

 

The Job:

Firstly, I removed the main core – header end of the pipe muffler – understanding the reducer was fitted to the core (incorrectly). I didn’t need to. Save yourself some rivets and silicone and leave it in. Only the end cap piece needs to come out.  Now that I know that, for you guys this should be a 2 to 3 beer job. (an hour or so).

 

When you pull it apart (drill out the end cap rivets with 4.8 to 5mm drill bit), here are some images of what you will find:

IMG_0186_zps73488e29.jpg
IMG_0185_zps97620b90.jpg

How it all fits together:

IMG_0188_zps6053d9a0.jpg

 

The end cap just slides right off, it’s stuffed with packing.

IMG_0189_zps5d2dc426.jpg

 

Assessing the baffle:

Now the narrow baffle tip is only about 16mm (5/8”). The outer baffle has an inner diameter (ID) of 33mm. The outlet tube it fits in has ID of 35.5mm.

The ID of the Yoshi spark arrestor/ baffle is 36mm. So final reduction size of an unbaffled stock outlet ID approximately matches that of the Yoshi.  An unbaffled RS4 outlet must be out around 41mm?

 

The main core of the stock muffler however has a much larger ID. So the gas is able to travel around and through both the narrow and broad sections of the baffle piece via the perforations. 

 

To remove the baffle.

I cut most of it off where it meets the outlet pipe. Simple. Hacksaw or angle grinder.  Of course be gentle with the pipe when holding in a vice, pad the vice and use the minimum or pressure required.

IMG_0191_zpsed6141d4.jpg

[Note: I'd already started prying at the inner sleeve here, hence it's bent up)

You can stop here, leaving your tailpipe reduction at 33mm ID, or you can grind off the spot welds and wrestle out the remainder of the insert and pick up 2.5mm of ID. This equates to an area increase from 8.54cm3 to 9.9cm3 – a further increase in flow area of 16%.

 

To remove remainder of baffle:

This is not how I got it, but this is how you should do it…

There are three spot welds about 8mm (5/16”) down from the end of the outer pipe.  They are equally spaced around the pipe – think Mercedes benz star.

The first one was smack in the middle of the seam where the baffle pipe is joined. I assume that is not coincidence. I was able to see another spot weld by a vague change in surface smoothness at that spot. If not you should be able to estimate the welds placement assuming the first is at the seam.
Using a dremel with a stone, grind the seam and focus on grinding down through the spot weld which will be 8mm in from the top.

 

Once you have ground through the weld, or weakened it substantially, hammer a scribe down between the pipes at just next to the seem. This will lift it enough to get a strong pointy nose plier in there and wrestle the seam apart and free of the spot weld.

IMG_0190_zps4361fcf3.jpg

IMG_0192_zpsa4b7647a.jpg

Above pic ^ - I should have started grinding 1/2" to the left of there where you can see the seam, perhaps you can make out the spot weld half way along the seam.

IMG_0193_zpsa2d158d2.jpg
Above ^ you can see a spot weld amongst the grinding, the blue spot where it's starting to break away. 

 

Once the inner pipe was ripped out, I ground down what was left of the welds, and bevelled round the tips of the pipes for reduced turbulence.
IMG_0194_zps7df81390.jpg

 

While I was at it I also turned my attention to the weld holding the collar at the head end of the header – it was lumpy and blobby where is started and stopped, and closed in the aperture. So a bit of stone work and sandpaper attention there:

IMG_0195_zps2b0d592c.jpg

 

Reassemble with new rivets and some silicone. If it needs repacking, do so :)

 

Testing:

I’ll have to keep you posted here, I’ll add it as I can. 

Sound levels. It's pretty quiet at adle, but a crack of the throttle reveals a very crisp response, accompanied by a barking note. Compared to the Yoshi RS4 with spark arrester installed; the note is coarser, deeper;  the volume level is notably higher, though not stupid loud, just dirt bike loud. My opinion is that it's slightly less loud than the RS4 left open, certainly no louder, with a coarser bark rather than the burbly thunder of the RS4. 

 

After some quick straight line drags my opinions are; that all of the power remains on the stock system, it's very responsive as you crack the throttle, moreso perhaps, than the RS4 with insert. With still a strong midrange surge which will stand her up easily under pure acceleration in the lower gears. It seems to retain the strong torquey mid that the baffled RS4 gives, while not losing the ability to rev out up top. I'm very happy with the power characteristic. 

 

These are just my opinions, and I’m afraid I never rode the bike with the restricted stock muffler, so I can’t tell you about the difference there in sound or performance.

 

Appendix

Weights: the unrestricted stock muffler weighs 2730g (96.3oz) vs the S/S RS4 muffler with insert weighing 2950g (104oz) - for a weight saving of 220g (7.8oz). This is with the stock baffle out which weighs 65g (2.3oz)

 

However the stock header weighs 571g (20.15oz) vs the RS4 header at 483g (17.05oz), to give a final weight saving of only 132g (4.66oz) to the stocker. 

Half that weight saving if the stock baffle is still in. 

 

 

 

 

Cheers :)
Brendan

Edited by brenno
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Thanks Slowgs. I thought this forum was in need of this info so it was worth the work involved to diarise it. I put in 40 odd laps at the local track today and I love the power characteristics of this set up. By far my favorite amongst the exhaust setups I've tried (Yosh open, Yosh with sparky, Stock open). It's crisp, responsive, free revving, torquey, and doesn't miss a beat. Love the ride. I could ride snug corners in third (stock gearing) and it didn't lag for a second, and the power surge though the mid toward the upper revs was brilliant - frankly I short shift and refuse to peak out my RPM. I'm a vet clubman and want my bike to last.   

Only flaw is it's loud. No louder than the wide open Yosh, And a crisp barkier note rather than the deep thunder thump of the open Yosh. But still too loud for me to ride on my property. So my next step will be to try free up the stock baffle a bit with some handy drill work, and reinstall it (via rivets). Then test that next weekend at the same track. 
Cheers folks. 

Edited by brenno
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Hi folks
Been tinkering today. 

As I mentioned my debaffled stock muffler, while performing brilliantly, was a bit loud for my taste. 

I've drilled out a heap of metal to open up the baffle insert that was added in the 11> models. 

If you are trying to open up your stock muffler without removing the baffle completely due to noise concerns, follow me on this one. 

 

I think the main thing here was I wanted to drill the washer shaped plate section between the narrow and wide pipes, to allow more through flow, rather than halting that much gas flow and sending it on alternative routes. 

 

You can see that done in the attached pic. I did this by drilling a ring of 3mm (1/8") pilot holes, enlarging them to 4mm, and then using a dremel to slot them along toward the weld. 

 

I also drilled a bunch of extra holes, enlarging some of the 2mm holes to 3mm, drilling some 3mm holes down the solid seam areas, and taking some groups out with a 7mm drill. I don't think you need to do this. I wanted to because I sawed off the baffle and when I reinsert this into the tailpipe I'll be covering some of the perforated walls, and thus the flow area. 

But I've actually calculated the amount of flow in all these little holes (yes I counted hundreds of little holes ;p), and even as installed from the factory, there are enough holes in the perforations to allow twice the open flow area than the 33m diameter core. So if you haven't sawed off your baffle (like me) then maybe just try drilling the washer section. 

 

A couple of other tidy ups I did include bevelling the main opening with dremel to present a sharp edge and a funnel shape into the narrow section. And I ground the weld (as indicated in pic) to allow smoother flow of gasses around the baffle. 

 

Mods.jpg

 

I just need to get hold of some more rivets so I can reinstall the end cap, and reinstall this baffle. Then I can test ride it and report back on sound and power characteristics. 

 

Thats all I got for now :-)
Cheers

Brendan

 

 

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Hey Folks. 

Just wanted to report with my subjective test opinions

These tests were basically drag runs, and wheel stand tests up and down a flat bitumen road. 

 

I put the less restrictive baffle back in the bike (see attached pic), and it does keep the noise levels at very acceptable levels compared to the open pipe, but it kills the aggression of the power. It's WAY less responsive/ snappy when I crack the throttle. It's slower to build revs and lacks the PUNCH we want for loamy or high traction race conditions.  With the stock pipe being even more restrictive I can see why aftermarket pipe sales are so huge. 

 

The removal of the baffle from the stock pipe altogether (as per OP) makes for a seriously improved experience. If you don't have to worry about sound levels where you ride, and you like explosive power, then I can highly recommend the mod. 

 

To put it in context I rode it side by side with the RS4; both with and without the insert. The RS4 definitely puts the punch back in the power (compared to the baffled stock). The wide open RS4 does offer the best power, but the wide open stock pipe matches it in my opinion - both in loudness and power. Then the RS4 with the spark arrestor is close behind, but with much more bearable sound levels. Still with strong punchy power but maybe a hair less of it - slightly less in the upper mid range.

The stock pipe with even the less restrictive baffle trails at a distant fourth place as a trail bike like power delivery in comparison - a benefit in minimum traction conditions only. 

I hope this has been or will someday be helpful to someone. Perhaps save them some big bucks on a pipe. Money some may not have to spare, or may be far more enjoyed on a 270 kit.  I can happily recommend the free mod of the derestricted stock muffler, riding location permitting. 
At the least, replacing or removing the baffle into the stock muffler to suit riding location is a 20 minute (and 9 rivets) job, which can be part of bike prep the night before. Less convenient than the usual one bolt baffle, but perhaps worth a $700 saving on a new pipe which really holds few advantages other than the sexy badge on the side of it and carbon fibre bling. 

Reinserted.JPG

Edited by brenno

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Do you know if this exhaust set up is the same on a '14?  I couldn't find a parts fiche for it.  

Hey Mudd

The answer is easy to find by simply taking a torch and having a look down your tail pipe. You'll see the restrictor easy enough about 5" in. I'm pretty sure it's the same muffler right through from '11. 

 

I am really happy with the performance gain (specifically responsiveness and surge of accelleration through the low and mid), It's really noticeable.  Though do be aware it's also notably louder. 

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   I was wondering if you stuck with the de-baffled  stock  exhaust since your write up .   I have a rmz450 and I just got done removing the baffle from a extra stock muffler  I had setting aside . I was wondering if I should pair it up with  a Yoshi header I have or keep it all stock . any advice?

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   I was wondering if you stuck with the de-baffled  stock  exhaust since your write up .   I have a rmz450 and I just got done removing the baffle from a extra stock muffler  I had setting aside . I was wondering if I should pair it up with  a Yoshi header I have or keep it all stock . any advice?

Hi Cody

I'm staying with the stock muffler with the baffle removed. I like the power and the sound the best. It gives the meatiest of both and a tolerable decibel level. I've been running a CW 270 kit and am still sold on it.

I've gone back to try the Yoshi RS4 again just a couple of weeks ago. With the spark arrester out I find it offensively loud, let alone what everyone else must think, and no power advantage. In fact I feel like there's less low end and mid grunt, and I don't ride the redline. With the spark arrester in I don't mind the sound, but it lacks it's balls some. 

With the open stock muffler I love it's wheel standability. Great mid range and torque, very meaty. 5th gear wheelstands are a piece of cake with the 270 kit now, despite my 200lb (I want to try a 14T front sprocket). And I can handle the noise level. I'd be happy to sell the RS4 but I'm only keeping it in case I stave in the stocker in the pine forest. 

Can't speak for 450 performance though. 

Edited by brenno
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How much louder is it. Do you think it would be fine at local tracks and no-one would notice?

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Nice write up. I just checked my 2014 RMZ250 and I don't see that restriction in the exhaust. I'm in the USA (if that makes a difference).

 

I also tried putting a rod through the end and there was no "step down" in diameter.

Edited by Mrbinkels

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   I was wondering if you stuck with the de-baffled  stock  exhaust since your write up .   I have a rmz450 and I just got done removing the baffle from a extra stock muffler  I had setting aside . I was wondering if I should pair it up with  a Yoshi header I have or keep it all stock . any advice?

The Yosh header won't do anything for you... it is built to the exact specs as the stock pipe, however I do believe it is a fraction lighter. 

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Yes Bdub - the Yoshi header is 88g / 3.1oz lighter than the stock. 

Mr Binkels -  The reduction is only about 6" in, if you can put a 1" dowel in there a good 8" or so then there's no baffle. It may just be the '11s and '12s? 
 

Kmx 193. The derestricted stock muffler should go fine at club days. I ran the open Yoshi and felt like one of 'those guys' on the track (I hate those guys). But the derestricted stocker is no worse than say a stock KX450F (had one of those).  

Cheers :-)

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Yes Bdub - the Yoshi header is 88g / 3.1oz lighter than the stock. 

 

Is that the SS header? That is def more than I expected. The Ti header feels quite a bit lighter. I wish I would have weighed it against the stocker or the SS Yosh header before I dumped them.

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