I spoke to my mechanic this morning and picked up the M4 exhaust that was on it before. He made a comment that bikes are designed to run with backpressure (ie. baffled exhaust) and that running a straight pipe will reduce power. I was under the impression that these kinds of aftermarket exhausts give you more power? Or just a different sound? I did some googling and found people discussing this. People are saying you need to adjust the carbs to run a little richer as with the straight pipe it will run leaner and possibly overheat the bike (as bikes are designed to run slightly lean these days?. Question is, the bike came with it installed already, the previous owner said he bought it like that. So I have no idea if the bike's been adjusted for the aftermarket exhaust or not. I have the bike manual and previous service stamps in there (Flywheels) - Worth giving them a call to see if they have any more information on it? Otherwise, is it safe to run the aftermarket one without damaging anything? Any comments welcome...
I would say give them a call to see if the Bike had been tuned to match the exhaust but I would say chances are it hasn’t but you never know. Also see, was there any mention of the jets and/or air filter been changed? And Is it just a slip on muffler or is it a full exhaust system? As with any aftermarket performance part (car or bike), to get the most out of it, it’s always worthwhile to get the vehicle appropriately tuned when its fitted. I am currently looking at what set ups are there for the Ninja, minus the full exhaust (production rules state I can only have a slip on muffler ) but regardless of what jets, filter and muffler I choose the bike will be getting tuned correctly on a dyno to make sure I get the most out of the bike and the parts I’ve put on. It will also prolong the life of the engine if the bike is set up correctly and is fuelling right. I believe this is something everyone should do regardless if the bike is for road only or track only.
I'll take some pics, not sure if it's just a bolt on or if its had a full system installed. I had the mechanic take the endpipe off and fit a stock/oem one from another Ninja
Here's a pic of the bike from when I bought it. Only thing that was changed was the endpipe (to a stock one, the one in the pic is sitting in a box at home) This is what's on there now:
yep mate that looks to be just a slip on, the rest of the pipe looks stock to me. Honestly i wouldn’t worry about it, might run ever and i mean ever so slightly leaner. standard exhausts are designed with fuel efficiency in mind, standard exhausts will have a larger baffle and therefore be more restrictive, non-standard will allow for a more free flow of exhaust gasses and therefor if done correctly will create better performance HP wise but not as fuel efficient (and I am talking a tiny difference). if you are just pottering or using the bike for commuting and your after fuel efficiency stick with the stock muffler, however if you don’t mind a non-noticeable difference in fuel and a far nicer sound stick the slip on back on. or if your pedantic like me, get a K&N filter, re-jet the carbs and get it tuned correctly, just my 2 cents
Well the 250's are pretty fuel efficient already, and I really do prefer the sound of the M4, so I will pop it back on at some stage. Thanks everyone
Back pressure is an oversimplification of quite a complex subject. Nice article here http://www.epi-eng.com/piston_engine_technology/exhaust_system_technology.htm As I understand it the tuning part is really between the exhaust valve and the collector, or point of section change, and is focussed on returning the negative pressure wave back to the cylinder at the optimum rpm. The shorter the headers the higher up you go. The remainder of the system has the function of venting exhaust gasses, reducing noise etc. Of course it should not be restrictive to the point of reducing power but there has to be some compromise in order to reduce noise. Hence, noisier free flowing mufflers can often yield some gain. A similar thing occurs on the intake side, albeit without the heat, pressure and speed. The exhaust that I am making for my Yamaha uses the muffler as the collector. All a bit experimental, and it remains to be seen if the mufflers can withstand the temperatures. cheers Blair
i was under the impression a simple slip on cant harm your engine but different length headers will mess things up, although my shorty exhaust has caused the bike to run richer.
No baffle causes less back pressure which is not good over a long amount of time as everything is tuned for the volume or air and combustion won't damage to much but just less performance
I've put the M4 back on but looks like I need a replacement lower clamp for the tube. The one from the stock exhaust isn't ideal but it's holding up so far.
Maelstrom has hit the nail on the head. Essentially fluid mechanics is complex and the exact effect is difficult to explain but I wouldn't be overly concerned. I've run aftermarket slip ons on ALL of my previous bikes with no problems at all, and I didn't bother getting any of the bikes tuned. It depends on the exhaust but I found for the most part I gained some smoothness throughout the higher rev ranges at higher speed due to less resistance in the pipe when using the slip on exhausts, but I did lose a bit of low end power. It was pretty negligible though, and I didn't mind it. In terms of baffled vs straight though, I'd tend to stick to something that mostly replicates the compression of the standard exhaust. Otherwise tuning is probably a good idea.
