Megaphone exaust with 520 sproket kit – GV125S Bobber
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Bike Model = : Hyosung aquila gv125s 2025
Hi I have a megaphone exaust on my sons bike it does sound nice and loads have said it makes the bike look bigger than it is eg 125cc. I have ordered a 520 kit for it to improve rpm more than speed as he dont realy go over 60mph anyway and not verry often at that speed. So my question is has any one had a aftermarket exaust same as what got eg open flow nothing in ther lol and still had gaines off the 520 kit 🤔 thank u. U no what 17 year olds are like they want it loud and nice than loosing its sound when ridding.
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Would be good to add a baffle to it as any 125cc doesn’t like riding without a baffle , then again you will get hard evidence when you take it to a Dyno Shop and they will tell you how much HP was lost using that can vs keeping a standard can vs using a harley factory can (has to be a factory can , not some aftermarket harley can)
Most we know so far on this forum is this thread
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Would be good to add a baffle to it as any 125cc doesn’t like riding without a baffle , then again you will get hard evidence when you take it to a Dyno Shop and they will tell you how much HP was lost using that can vs keeping a standard can vs using a harley factory can (has to be a factory can , not some aftermarket harley can) Most we know so far on this forum is this thread
https://hyoriders.club/forums/topic/exhaust-suggestion/embed/#?secret=69QgSkqxwy#?secret=p7gX9GhALk
yes he took the bike out and have said it dont no how people are getting up to 70mph as my bike is sitting at just over 8k revs in 5th gear at 55mph ? But his is a 2025 so no a bit slower and has only 140 miles on from new so not even broke in yet. Does that sound right 55mph 8k revs in 5th or is that still high 🤔
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10,000 RPM is a safe limit , but because you are running in the engine, you want to stay around 8k until its about 600 miles run in, so take your time. The benefit is that your have a way stronger chain set as you physically found out, he wont be going back to 428s
The customers who made rave reviews on their bikes had stock exhausts you saw in pictures of the shop OR they used Original Harley Exhaust as quoted above ^ = The GV125 since 2001 (carb model) and currently EFi models (2019+ onwards) still hate random exhausts , so its a matter of trial and error to ensure the right exhaust is not losing “lower bottom torque”
Top speed doesn’t matter if you’re under 50mph , it is the “torque” that matters for quick city sprints or going up hill , the exhaust plays a huge part in it. Some people on facebook will tell you (it is a 125 , who cares) are clearly people you do not want them to service your motor next time.
125s my experience repairing them for customers always preferred a proper exhaust (expensive ones) + a baffle that is about the size of a 10p coin.
if ANY exhaust is as LONG (length) as the OEM Hyosung stock and has about a 10p hole size to exit gas = This seems to be a sweet spot. Europeans are using Harley Exhausts stripped from real harleys (a real harley exhaust will make itself known that it is not a knockoff version you see in china)
The name of the harley exhaust to try is in this thread
Remember, it is a new iron maiden, run her in first and watch the revs gradually settle once he is in top gear. After 600 miles, we should have a service again, then it should behave like everyone else on this shop said , “accelerates quicker off the line , but each gear feels longer ” – This is the balance you want to break out of the 75-80+ mph barrier , Factory speed is 60-65 max at max 12k revs!
Feel free to experiment back on a standard exhaust , as you’re going back to the factory setup with a faster chain thats all. Don’t pay too much attention at top speed, you want to find out does it “pull harder” on stock exhaust or this loud one ? Test the torque first, more speed will come from the bottom low end torque (how much pull it has in gears 1-3 = less struggle to get to top gear.) , don’t be afraid to go between 8k revs and 10k revs
It is OK to rev to 10k rpm in gears 1-3 to build momentum for the bike, then top gear will cruise in lower revs like 8K (kinda pointless to ride at 4-5k revs , its a heavy girl!)
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