[ngrate]

Opinions and comments. Wonder how much the stage 3 mod will cost?
Millennium Technologies' New Big Bore Kits Expand Honda CBR250 Power Output



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[MotoMike]

I can imagine that both the stage 2 and 3 kits will be pricey.

With the stage 1 kit priced at $375 exchange and resulting in an increase to 285cc & 4HP, it would be interesting to compare that stage 1 kit with the alternative of doing a CBR300R crankshaft swap (increasing displacement to 286cc), both in terms of cost and performance gain. Obviously we don't yet know what the cost of a 300R crankshaft will be, but one might assume that it should be fairly close to the price of the CBR250R crankshaft, which is currently about $165, plus $50 for gasket sets (Partzilla.com).

 

[chriscbr250r]

i have bought the 305cc big bore kit putting it on soon

 

[MotoMike]

i have bought the 305cc big bore kit putting it on soon

Is that the Takegawa kit?

 

[chriscbr250r]

got it from e bay Taiwan,, japanese kit 385 us

 

[chriscbr250r]

Is that the Takegawa kit?

i got it from ebay from tiawan jap kit 305cc they say with piggy back its good for 34 bhp and 24 nm talk

 

[ngrate]

i got it from ebay from tiawan jap kit 305cc they say with piggy back its good for 34 bhp and 24 nm talk

Don't you have to beef up the engine mount to accommodate the additional power? Anything else. Please report on how much time it took. Thanks.

 

[gromit]

chriscbr250r: expanding a little on what MotoMike just said: The new cbr300r that is coming out soon uses a stroked crank assembly with a shortened connecting rod to increase the displacement of the engine. By using a 305cc big bore kit and the new crank assembly you would have a displacement of 340cc. That might be something worth considering. The crank assemblies come with the connecting rod installed. The shortened connecting rod insures valve clearance with the longer stroke.

 

[chriscbr250r]

chriscbr250r: expanding a little on what MotoMike just said: The new cbr300r that is coming out soon uses a stroked crank assembly with a shortened connecting rod to increase the displacement of the engine. By using a 305cc big bore kit and the new crank assembly you would have a displacement of 340cc. That might be something worth considering. The crank assemblies come with the connecting rod installed. The shortened connecting rod insures valve clearance with the longer stroke.

true but do you think the valves and head gaskets could cope with that extra pressure whats the feel on this

 

[chriscbr250r]

Don't you have to beef up the engine mount to accommodate the additional power? Anything else. Please report on how much time it took. Thanks.

no its fine it took 4 hrs to fit easy job fitted it to my cbr that i making this moto 3 body kit it will be for sale soon

 

[gromit]

true but do you think the valves and head gaskets could cope with that extra pressure whats the feel on this

I see what you mean, that would be a noticeable bump up in the power range from a single cylinder commuter bike engine to a more racing level engine. I really don't know if that would be pushing the limits of the valves or the head gasket.

 

[chriscbr250r]

chriscbr250r: expanding a little on what MotoMike just said: The new cbr300r that is coming out soon uses a stroked crank assembly with a shortened connecting rod to increase the displacement of the engine. By using a 305cc big bore kit and the new crank assembly you would have a displacement of 340cc. That might be something worth considering. The crank assemblies come with the connecting rod installed. The shortened connecting rod insures valve clearance with the longer stroke.

i like this idea but we need to get some expert advice on this i.e. can the conrod take this extra pressure also the metal head gaskets the ports valves ect ect head so on
it would be cool for about 40 up bhp though im sure ohhhh yeahhhh

 

[MotoMike]

It's probably safe to say that taking the stock 250R motor, and building it up to a 341cc displacement* with the 300R crank & a 305cc big bore kit could yield an impressive power gain... but the big unknown is what kind of reliability you'd have with such an engine.

* Besides the obvious need for a programmable fuel controller, I'm thinking that the 250R's stock 38mm throttle body wouldn't flow enough air to feed the 341cc displacement, so that would be another issue to address.

All in all, building a 341cc would certainly add up to some big bucks (assuming you do the whole thing right, with no half measures). Personally, I'd just buy a bigger bike like the KTM RC390, which at the end of the day would probably cost less.

 

[MotoMike]

I see what you mean, that would be a noticeable bump up in the power range from a single cylinder commuter bike engine to a more racing level engine. I really don't know if that would be pushing the limits of the valves or the head gasket.

Which brings up the question... what class would you have to race such an engine in, and what other bikes would you then be competing against in that class?

 

[600k2]

Bore And Stroke 76mm x 55mm

305cc overbore kit is 8mm over and 286cc crank is 8mm over.

84 x 84 x 63 x .7854 = 349cc

 

[600k2]

Which brings up the question... what class would you have to race such an engine in, and what other bikes would you then be competing against in that class?

90hp Suzuki SV650's (in super bike trim)

 

[600k2]

KTM's 350 exc-f has a 349cc (88 x 57.5 mm) 4 stroke single, with a 42mm throttle body and larger titanium valves. They also replaced the rod bearings from needle to babbit style bearings for longer life. This engine is over 45hp from the showroom floor.

What do you think the cbr can acheive bored, stroked, shaved head, race cams, valve springs, larger valves, and tuned on race gas? I haven't looked in to the injector or fuel pump specs, it might need upgrading to keep up. NSF250R uses the same injector as the CRF450R, so maybe use a 450 injector as long as the pump can keep up volume and has the correct pressure.

 

[roadster]

chriscbr250r: expanding a little on what MotoMike just said: The new cbr300r that is coming out soon uses a stroked crank assembly with a shortened connecting rod to increase the displacement of the engine. By using a 305cc big bore kit and the new crank assembly you would have a displacement of 340cc. That might be something worth considering. The crank assemblies come with the connecting rod installed. The shortened connecting rod insures valve clearance with the longer stroke.

If the longer stroke doesn't change the piston position at the top of the stroke then surely it must change it at the bottom. Are their any differences in the barrel? If an old one is used it must be at least honed to make sure the rings aren't destroyed by travelling lower in the bore than previously.

 

[Joeboo]

I have no doubt the stock bottom end will handle 45hp, I've had a sr20det (140hp stock) & wound it up to 350hp with stock internals... That sucker is still running 5 yrs down the track & sees the drag strip, power cruse & summernats all the time.
Done rite with the 300s crank & rod & 305cc piston kit, bigger valves, cams etc it should do 45hp+ and be quite reliable , it's not like its a drag bike. Used on the road for road use, twistys it should live as long as a stock 250.

 

[chriscbr250r]

I have no doubt the stock bottom end will handle 45hp, I've had a sr20det (140hp stock) & wound it up to 350hp with stock internals... That sucker is still running 5 yrs down the track & sees the drag strip, power cruse & summernats all the time.
Done rite with the 300s crank & rod & 305cc piston kit, bigger valves, cams etc it should do 45hp+ and be quite reliable , it's not like its a drag bike. Used on the road for road use, twistys it should live as long as a stock 250.

i think im going to try it i live in thailand so its cheap to buy the parts here it will work or blow up ...nothing ventured nothing gained