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Discussion Starter #1
With 16000 happy km so far I'm getting interested in how to improve the top speed and performance in 6th gear. Is there a way we can make it free revving? Seems to bog a bit and difficult to get over about 9500rpm in top gear, even if redlining in 5th. I've topped out at an indicated 160kph which was 145kph on the GPS, but many of the travelling highways here I keep the throttle pinned for 4-5 hours when travelling across the country (Thailand), and would like to be able to get it higher than 9500rpm (or so) in 6th.

Any ideas on what we need to do?

Am thinking of keeping an extra sprocket to reduce the rpm at high speeds, but other than that is there some sort of limiter that can be removed or anything?

Thanks.
 

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Sounds like you have reached the limitations of this bike; in other words, out grown it. Time to upgrade to a larger bike.
 

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Discussion Starter #3
Yes, I plan to upgrade to an Er-6n (650) in about a year.

Until then I've a lot more touring to do. A lot of that will be on empty highway with no police - pin the throttle time. GPS speed of 140-145kph is okay, but I'd like to open up 6th a bit more.

Anyone know what's required?
 

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Yes, I plan to upgrade to an Er-6n (650) in about a year.

Until then I've a lot more touring to do. A lot of that will be on empty highway with no police - pin the throttle time. GPS speed of 140-145kph is okay, but I'd like to open up 6th a bit more.

Anyone know what's required?
For a stock bike nothing is "required". A 250R redlines at about 10,200 at about 165KMH true. I've had mine to 168, only limited by the stock gearing.
If you want to modify the bike for more speed, replace the exhaust to get a little more power, and change the sprocket(s).
Another thread mentions shorter gearing (bigger rear sprockets). I (and others) are still waiting for longer gearing (= go faster).

Sounds like you ride fast a lot, be careful man.
 

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My friend has a honda cbr 600rr, he put a after market exhaust with a power camandor and a air&fuel intake kit then got his bike dynoed and got a 30 mph jump in his top end speed. Exhaust is already out there but I haven't seen a power comandor or juice box for the 250 yet. I'm not saying you'll get an extra 30 mph but I think 10 to 15 mph should be doable.
 

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But my friends mpg dropped quite a bit after he put in the mods in and the 250's tank is 3.something gallons so you could end up filling your tank more often then you'd like
 

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Discussion Starter #7
I've already ran (and still own) a full system exhaust, with the ECM reset, top end speed difference was minimal, you really need a powercommander or juicebox added to make a difference.

Gearing, as changing that to increase top end will decrease acceleration it's something other than what I'm talking about.
 

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With 16000 happy km so far I'm getting interested in how to improve the top speed and performance in 6th gear.

Any ideas on what we need to do?

Am thinking of keeping an extra sprocket to reduce the rpm at high speeds, but other than that is there some sort of limiter that can be removed or anything?

Thanks.
I took this to mean why am I not able to redline in 6th gear. That's why I made the suggestion about exhaust ect. Because you don't want to redline in any gear, redline refers to the maximum engine speed at which an internal combustion engine and its components are designed to operate without causing damage to the components themselves or other parts of the engine.
So if you raise your top speed your redline will raise aswell. Correct?
 

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Discussion Starter #9 (Edited)
Sorry for the confusion.

Bike has no problems redlining to the maximum in all gears up to 6th. In 6th gear though the acceleration is slow to get it up and into the redline on the tach. I've been able to take it to 160kph indicated which is probably close enough to touching the tach redline. The 160kph indicated was really 145kph on the GPS, or exactly 90mph, which is around the top speed others mention.

What I'm interested in is ways of killing off this drop when going into 6th, and have it free revving well into the redline like you can do in 4th and 5th (and all the gears below). I'd like to get it up to 11000-11500rpm in 6th.

Is it simply gearing or is it some sort of limiter, is there a way of fiddling with the ECU to change it, etc?
 

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IMHO I think the limiting factor now is camshaft timing. The engine is not putting out maximum power at redline. Rather, by design it is at a lower RPM not far from the maximum torque RPM. That's what makes the engine so good in standard form. So, I agree, taller gearing should improve top speed as it will alow the engine to stay closer to it's designed peak power RPM. I think you will find it would still climb to the RPM you see now, but at a slightly higher speed. I would like to fit a 16t front sprocket to mine also, but I am not sure there is room. Or, by fitting race cams (Which must be due on the market soon?) the peak power will be at a higher RPM at the expense of low RPM torque.
 

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100 mph

IMHO I think the limiting factor now is camshaft timing. The engine is not putting out maximum power at redline. Rather, by design it is at a lower RPM not far from the maximum torque RPM. That's what makes the engine so good in standard form. So, I agree, taller gearing should improve top speed as it will alow the engine to stay closer to it's designed peak power RPM. I think you will find it would still climb to the RPM you see now, but at a slightly higher speed. I would like to fit a 16t front sprocket to mine also, but I am not sure there is room. Or, by fitting race cams (Which must be due on the market soon?) the peak power will be at a higher RPM at the expense of low RPM torque.
All true. I second this. I don't believe there is an electronic speed limit on the CBR250R as there is on the PCX scooter (limited to 60 mph). The top speed is limited by horespower which is declining again after 8,800. Get a better slip on that works properly such as the Two Bros, and gear longer to get a faster top speed to occur at 8,800rpm. I will find out soon for myself as new 15T and 16T front sprockets have been designed and are in line for production. I believe an exhaust without any fuel cheater box (Two Bros dyno image on the right) and a 16T will break 100mph/ 160kph actual.
 

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All true. I second this. I don't believe there is an electronic speed limit on the CBR250R as there is on the PCX scooter (limited to 60 mph). The top speed is limited by horespower which is declining again after 8,800. Get a better slip on that works properly such as the Two Bros, and gear longer to get a faster top speed to occur at 8,800rpm. I will find out soon for myself as new 15T and 16T front sprockets have been designed and are in line for production. I believe an exhaust without any fuel cheater box (Two Bros dyno image on the right) and a 16T will break 100mph/ 160kph actual.
PS.
Racing cams and a fuel box would then take the 16T gearing to 180kph. And cut the fuel economy in half.
 
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