Stock Exhaust Mod


Have seen a couple of posts on this, but none recently and not ones that have been what I'm after, so I'm going to mod a stock can myself and see what the result is like.

So I saw this mod which looks really good at turning the stock exhaust into pretty much a straight through pipe, but for me it's a bit too on the raucous side and I want a more subtle tone change

So the stock exhaust looks like this inside:



The gas flow is sent into the middle chamber, fills the area, passes into the right chamber, fills and then through a pipe underneath the short upper pipe that's visible into the left chamber and then finally into the long pipe all the way to the outlet.



Not great artistry but gives you the idea.

So in the video, he guts the lot and makes a straight through pipe. I've also seen a video where a guy cuts the right most outlet pipe, but the effect is minimal, since the short pipe is still quite a restriction and leaving the other pipes open still allows a lot of the gases to be sent the long way round.

My thinking is it will be better to block that short pipe in the right panel, then cut the section of outlet pipe, so the gases only travel into that middle section before filling the chamber and then going straight out. This isn't far off being straight through, but the fact the gas fills the central chamber allows some slowing of the gasses speed and disturbs the flow enough to reduce volume to (hopefully) a nice level.



This also has the benefit of only needing that small middle section to be opened up and a couple of cuts with a reciprocating saw to knock out the central piece. Block the small pipe off and also the section now open to the left chamber and the flow is straight through to the outlet.

Found a stock Tracer exhaust on ebay for a nice cheap price so I'll not be hacking up my original (if it's a tad too loud can still use that for MOT's etc) and will get the angle grinder and welder out when it arrives and let you know how it goes. As I say, hopefully it will give a much nicer deeper tone but not be anti-social or draw attention from the police etc.
 
Last edited:

Timbo108

New member
Do keep us posted. Sounds like something I would go for. Bought a plasma torch I'd like to give a whirl.
 

stevecbr

Member
I modded mine back in 2014. I cut the pipe in the right hand chamber right out, and drilled some holes in the plate between the middle & right chamber. I didnt touch the cat. According to my db app on my phone, it was 2db louder afterwards. Louder than standard, but not obnoxiously so. Have done trackdays with it fitted, and no problems at MOT time. Bike now done 34000 miles with no issues, its still on original fuel map (never had it reflashed)
 
Had a bash at the exhaust yesterday.

The one I got from eBay is practically brand new - I reckon the guy selling it must have bought the bike then pretty much straight away got an aftermarket exhaust and simply flogged this to scrape a little money back. Crazy really, for the price of the stainless and the cat I bet I could flog it for scrap for more than I paid for it.

Anyway, because the Tracer exhaust has brackets on the top, where the MT09 doesn't (which is the one pictured previously) I decided to change my plan of attack. Turning the exhaust over so I was coming in from underneath it was obvious that simply opening up the end instead of trying to mess around in the mid section was going to be the best option.

Bit of angle grinder action later and I had the end open.



Got my reciprocating saw out and simply cut the exit pipe out and a large chunk of the end plate out which has opened the flow up straight from the cat into the end chamber which is then free to flow out of the outlet or bounce around to fill the other chambers a bit. It's a bit crude looking, but no way to get the entire end open without trying to remove the pipes on the right, so decided this will open the end up enough for now. You can just see the end of the cat in the opening.



Since the exit is still the same size as normal and the cat is still in place, I don't expect sound to be increased to any anti-social levels, but hoping that since the gases hit the end chamber less hindered, will give a bit more of a deeper tone. Will put it back on the bike week and do a before and after vid to see what the effect is.

If it's been a waste of time and hardly effected it at all I will open it back up and seal off the other pipes completely so it's forced to go straight out - or simply gut the whole thing for more of a straight through effect like in that guys video and see what happens (using perforated pipework and wadding). For the price I paid, it was cheap enough just for a bit of playing around just for the hell of it.
 
Well exhaust swapped over now, a quick dab of copper grease on the studs (might as well while its off) and the mod exhaust in its place.

I'm really happy with the outcome to be honest, which is more a happy accident as it's all guesswork, but the tone is much deeper and a slight rasp but not too loud. Put the dB meter nearby (same distance each time) and its around 10dB louder and gone from around 90-100 to 100-110. With an average around 105 that's trackday volume which is around normal aftermarket exhaust volume which is perfect.

I've used this meter before to check before track days and it reads a bit high as I thought I'd be pulled up on track but it passed fine when was tested, so in reality I reckon I'm nicely in the range. Either way it shows the increase in volume nicely.

Anyway, here's a before and after volume of videos. Mobiles don't have great mic's but it's definitely a much nicer sound - with headphones it's easier to hear the deeper tone.

Before

After
 

Timbo108

New member
Awesome. Thanks for the follow up. Sounds much nicer and keeping the stock look is key for me. Let us know if you experience any lean pop on decel or any other issues. Have fun.
 
Awesome. Thanks for the follow up. Sounds much nicer and keeping the stock look is key for me. Let us know if you experience any lean pop on decel or any other issues. Have fun.
Thanks, yeah I'm really pleased with it - I also wanted to keep the stock look, but just get that little extra tone to the exhaust note.

Came into work on it this morning and really pleased with it.

Even with ear plugs in I can hear a nice low rumble at idle and it's got a nice growl on the power. Nothing too much at all, only marginally louder even at higher revs, so it wont be attracting plod or annoying people, but give it a blip riding through traffic and it gives a nice bark that you expect more from a road legal aftermarket exhaust with a baffle in.

No popping or anything on the overrun, however I have flahsed my ECU to disable the clean air system stuff so not sure if it would make a difference on a completely stock bike. The fact the Cat is still present and it's still entering a large(ish) chamber before exiting I wouldn't expect too much of that anyway, but can't say for certain.

Also, I haven't noticed any difference in how the bike feels - the "bum dyno" can't detect any loss or gain in power. I didn't expect to as the exit pipe is the same size as before, so the restriction through the Cat and final exit is the same regardless.

Final comment is would I recommend doing it or is it worth it?
Personally I think the result is worth it if you want a little more volume but not be antisocial and keep the stock look. I reckon it will go through MOT no question.

Although I bought a stock exhaust (in case anything went wrong), having done it I'd now be happy to recommend just going for it on your own as long as you have the tools and are pretty handy with them. Minimum would be an angle grinder and ideally a reciprocating saw to knock out the internals. I also used a step drill bit to cut large holes in the 'bulk head' to get the saw blade started. Then finally a MIG welder to seal it back up. I'm still learning welding and am very much a hobbyist with a long way to go, but this was a pretty easy job and the metal is a decent thickness not to burn through too easily.
 


Top