TL;DR: Top speed I’ve managed (so far) on mine with 180cc kit, 160cc injector and longer duration cam, with PCV + Autotune/wideband: 89mph.
So I’ve noticed there’s people searching on this topic so I’ll share what I’ve discovered so far, hopefully it’s of some use.
Top speed on mine when I got it, as 125cc on stock 14t sprocket was 83mph (indicated). That was absolutely throwing-it-down-a-hill-with-the-wind-behind-you, the most I could get out of it. 83 seems to be a fairly common top speed for stock bikes. Some other people have claimed 86 out of a stock bike but I can’t verify that myself and that wasn’t my experience.
Ok well you probably know how I feel about facebook products but if anything’s going to get me to cross that line it’s bikes. And it did..Actually so far I quite like it. Lots of nice picsand seems like lots of similarly bike-obsessed ppl but less noise than fb. Biker twitter has decidedly less outlaws than I was hoping for so perhaps Insta is a better place.
Either way..if you’re on there, of if we’ve seen you whilst out riding, please do follow + say hi 🙂
Let’s see if insta is a better outlet for my photos…
For about a year I’ve been looking for a cheap frame to mount the turbo motor in, kinda because I was hoping it would be easier than making a motor stand..You sometimes see written off frames o ebay for peanuts and I was hoping to get one and perhaps cut out what I needed if it couldn’t be put onthe road anyway. You can get clean frames with paperwork from italy and germany but they’re usually £500+ and that’s a bit much to spend on somethign wich may never even make it to he road…but then at long last I found this one the other day in Germany.
Ok so this seems to be an ongoing urban myth, whether it’s chavs drilling the airbox of their mum’s Fiesta 1.1 popular or little 125s, or even big bikes, people seem set on the idea that airbox designers are actually our mums who are trying to sneakily slow our bikes down. or something.
Why am I even going down this road?
On my bike I’ve shown the exhaust side of the engine quite a lot of love and attention, but despite the nice, big-bore shiny pipesness, she continues to run better with a little baffle in the end, like so:
The best reason I can come up with that the bike runs better with a smaller diameter exit/baffle in the end (effectively restricting the flow again) is that perhaps the exhaust is a bit much pipe for the bike – and by that I mean for the amount of air the engine is moving, the pipe diameter gets too wide at the end, which ends up with the gasses slowing down too much and actually impeding scavenging of the exhaust system. Or maybe there’s some sort of sound-waves stuff going on like with two-strokes.
Either way with the baffle in you get a little bit of torque around that 70mph point where you shift into top gear. With the open pipe it didn’t have the oomph to push through that but with the baffle it does (albeit slowly).
A couple of months ago, under what turned out to be ideal conditions on a private runway, thanks to that baffle we hit 85mph. That was on a 15t front gear too so would have needed even more torque to make it through to the power band.
And it was absolutely equal parts terrifying and exhilarating..,as you would expect flying along on a glorified moped! 😀
So I found this thread which possibly explains what’s going on with my exhaust (2nd post particularly relevant).
i think this may be about gas velocity, which would sorta explain the current counter-intuitive performance improvement by adding the baffle in the can. I’ve also realised that it might be better still if i take the forward baffle out (the one which came with the exhaust system) and only have the rear one…that way i might get better performance still and regain some of the nice sound.
It may also do nothing/make it slower in which case it’s going back how it was….gonna find out today hopefully.
I did another quick run across town just now with the baffle in and it definitely seems quicker. I dunno if that’s because I’m less conscious of the rpm and so ride differently but it definitely felt like it wanted to *go* again. Much grinning when I got home.
I guess it’s possible that at low/mid rpm the little bit of restriction might improve torque somehow – I guess there’s sound waves and stuff going on in there to some extent like a 2-stroke. I didn’t really get chance to go flat out though and that’s where I’d expect the baffle to be a restriction…will have to see. Didn’t seem to be a problem revving high at speeds up to 50ish though, kept finding i had to back off a bit.
I’m still not loving the sound but stealth is better and obviously whatever’s quicker wins. Interested to see how it does on a test run. I guess I need to figure out some sort of timing malarkey I can work with gloves on first, though even just seeing how it performs when flat out with the baffle would be interesting. Next time she’s on the dyno I guess we’ll find out for sure but that won’t be for a while yet.
