Big Bore Kits..

[fatjames]

So, I was looking on Wemoto and saw that Barrel and Piston - Big Bore Kit's are for sale, at 276 quid for a CBR125.
So, lets ignore licence/insurance for the moment. Has any one used one of these kits? Is there anything else to consider? Anyone know about power/speed increases?

[Frost]

The asian bikes are CBR150's so you can fit a top end from one of those, but i think they have a 4 vavle head rather than a 2 valve so you'd also need the head and cams. Fitting a big bore kit would require at very least the carb to be messed with, possibly a larger carb too.

[P.addy]

Havent bothered looking but is it the 166cc Athena kit?

The 150 if you can find parts as said...swaps on. The Athena comes with all the bits and bobs and gives a marginal increase.

[fatjames]

[P.addy]

Well... unsure with the FI, if its anything like the cars i've had, the injector size goes up along with any form of power increase. Talking 100hp increases though

I'd assume its for the pre FI bikes anyway? surely the manifold is for a carb? Either way, id probably expect a little more low down, but nothing other than maybe 10mph top end absolute max? Down a hill.

If anything, I might end up doing if I can find a cheap enough kit on ebay.

EDIT : My apologies, they do both the carb and FI version

Also..

[Frost]

[Kickstart]

Hi

32% increase in capacity won't give a 32% increase in power (as you will likely land up with a horrible shape of combustion chamber, even if you can rev the engine just as hard), and 32% more power won't give you that much more top speed.

Playing around with the figures, assuming a cda of 3.6 then the 10kW of a stock CBR125 would be enough to get it to do 78~79mph while 13.2kW would make it hit 86~87mph.

All the best

Keith
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[fatjames]

[stevo as b4]

Id expect about 2-2.5bhp more at peak power revs as a maximum figure. the torque increase should be more though.

The CBR was dyno'd by BSD at 11.95bhp r/w, which is very good for a claimed 13bhp engine. Superbike got a tested true 73mph out of one at Bruntingthorpe. Again the top speed achieved is IMO very acceptable for a fairly upright not quite fully faired 125 with 13bhp. Bear in mind you'd be seeing silly speedo readings of close to or just over 80mph.

PB did a load of work on the YZF125R and went from 12.13bhp to 18bhp r/w with a Malossi 180 kit and exhaust etc. They did get better acceleration out of it, but as for top speed it was little better. They didn't have enough sprocket choices to have a proper play though. You'd likely see 5-8mph more in normal prone conditions, for this sort of mod i would say.

TBH if you can make a CBR125 top 16bhp r/w and a true 80mph, then id say thats very good considering, and all you could expect really from a 4stroke 125 with a big bore kit.

To get the most power possible you would need expensive headwork, bigger valves, aftermarket cams and a way of fully re-mapping the fueling and ignition. Even with that kind of expensive engine work, topping 20bhp at the wheel could be extremely difficult to do reliably.

[P.addy]

I get an indicated 85 out of this thing daily...

https://a1.sphotos.ak.fbcdn.net/hphotos-ak-snc6/185718_195150683843164_100000447005731_653298_652493_n.jpg

Not bad for a distinct lack of fairing Wouldnt mind trying the 166 kit.

[fatjames]

[P.addy]

Take about 10% off your speedo...maybe a few more as they are stupidly optimistic

[fatjames]

[Kickstart]

Hi

Pretty much impossible for a normal speedo to be accurate. They rely on the diameter of the tyre, which varies with wear and between brands of tyres even if nominally the same size, and also with speed and load (as the tyre deforms).

Legally they must read the actual speed or higher. The limit is 10%+8kmh over the actual speed for a production sample.

Beyond that the speedo is the cheapest thing to tune to make a bike seem faster than it is .

All the best

Keith
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[fatjames]

[CarlosCBR]

90 on my speedo reads 84mph true speed GPS. Not too bad
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[fatjames]