Most people get an R125 and slap the biggest exhaust they can on it and call it good..but especially without fuelling adjustment you’ll likely find your bike is actually slower (top speed less by 2-3mph indicated) because the airflow of the exhaust isn’t optimal for the cc of the engine.
So yes you can have the dope sounding pipe and scream down the road setting off car alarms and deafening everyone but at what cost?
I don’t fully understand the physics in play in each exhaust but it’s easy enough to tell whether something sounds/feels “over-piped”, just as it’s easy to feel when something is restricted or “under-piped”. Maths aside, the answer lies somewhere in between those two sizes and it’s easy enough to A/B test.
So when my bike was 125cc I had a stock 61mm ebay baffle which (based on testing) gave me the best top speed and acceleration. But once I moved to 180cc then the baffle was too restrictive so I built the newer one which added some thickness to the material to dampen the “clackyness” it had before, and also a series of holes which amounted to roughly +40% of the previous diameter. My hope was that the smaller holes would allow the same amount of airflow for the bigger cylinder but perhaps break up the pulses a bit for a smoother sound. That was very successful and she sounds amazing now, lovely burbles and *thrummms* and pops in the right places. So sweet 🙂 We also set a new top speed wiht that setup so thus far it seems to be better than the other one.
The baffle is held in place by a bolt in the edge, and by drilling that hole slightly offest it means you can also vary the depth of the baffle so it’s 5-10mm one wayt or the other. Since this exhaust stuff is largely about sound waves and their timing as they bounce around inside the can, being able to adjust the length/timing of that can mean a couple more mph on your top end. One way round will work better than the other, so like everything else I’m doing, this becomes part of a way of testing your way to a faster bike based on actual evidence for your exact bike/situation.
Your bike will probably be different. You might not be able to mount a baffle the same way.. don’t worry. That’s something we’d figure out. All that was needed to mount this was to drill a small (5mm) hole in the exhaust (on mine it’s on the underside – you can see the little allen bolt), Then it just needs a small ellen key to remove so you can easily do a test run with it one way around (or with a different baffle) and then test wiht this one (or the other way around)..testing is a huge part of tuning. This dumb little bit of aluminium added about 3mph to my top end.. and I’ve had to *work* for every mph over the original 82 so to just add 3mph on the top was quite impressive, and it sounds awesome.
Whilst the size/area of the holes needs to be whatever it needs to be based on the engine, we can make the holes in different ways and that affects the sound. I wanted thrumms and purring/burbles and pops.. it’s tricky to get a single cylinder 4-stroke to sound nice but I think it worked out extremely well.
