Different horsepower even different rpms?

[TxTaoRider]

I've been sorting through the internet comparing different cg250 powered bikes and noticed something interesting.
CSC, probably the most honorable of the sellers list their official horsepower at 16.1 @ 7000rpm. The brozz and tbr7 list their's at 15hp @ 7500rpm. A generic ebay cg250 is rated at 14.5hp @ 6500rpm, and rps lists the hawk at 14.1hp @ 7000rpm.

My question is why is there 12.5% hp difference from the lowest to the highest (both on bikes with lean jetting and catalytic converters)? Why is the generic motor so low assuming it's not measured with emissions devices installed? All have similar compression ratios.

Does the tt250 have a better cam or head or airbox? Just curious...

[Bill Hilly]

It may be in differences between carb set up. I don't know if they are all jetted the same, or even if they use the same carb. Some may even tune them on the dyno, or average the pulls of several motors, and some may just dyno one.

[franque]

Some have better quality castings, the CSC for one, but it could be down to factory airbox design and factory exhaust when they're emissions testing for the EPA.

[Bruces]

Some are just lies and guesses .

[XLsior]

Could also be down to air quality and elevation density depending on the location of testing and also quality of testing equipment.

Short answer:China.

[Megadan]

The head casting quality is probably the biggest reason why the CSC motors are rated as high as they are. They also have the catalyst in a better location that doesn't choke the motor to death like the Hawk and other bikes. The rest of it mostly comes down to carb tuning, and a tiny bit of it from the little extra bit of compression that CSC's engines have from their thinner steel head gasket.
As far as the airbox design, that is probably the least of the potential factors.

Think about how different a Hawk is in terms of performance once you decat the exhaust and jet the carb properly. Those two changes alone were good for a 4-5mph difference in top speed from my own experience on my first Hawk with 17/45 sprockets.

[cycleway4]

I'll go with Bruce's explanation.

[TxTaoRider]

Has anyone compared the heads of the csc to the hawk side by side?
I can tell you the intake port on my tbr7 is about 1mm smaller than the brozz head I cleaned up the bowls on. But I didn't measure to see if the ports were located higher or lower in the head. 1 or 2 mm in port height can make a measurable difference in flow.

[Oldenslow]

I frankly don't put much stock in any of the horsepower numbers thrown around about these engines. The number you arrive at under the best of circumstances will depend on how it's measured, anyway. If any of the Chinese motors have ever actually been measured, there's no way of knowing how.

[Megadan]

Originally Posted by TxTaoRider

Has anyone compared the heads of the csc to the hawk side by side?
I can tell you the intake port on my tbr7 is about 1mm smaller than the brozz head I cleaned up the bowls on. But I didn't measure to see if the ports were located higher or lower in the head. 1 or 2 mm in port height can make a measurable difference in flow.

A couple of us have (Jerry being the other I know of). Both ports have a much better shape to them in terms of casting quality, and the exhaust port in particular has a much smaller protrusion into the roof of the port around the guide making it much less restrictive stock for stock.

I do know from word of mouth that others have stated the Brozz head is also a better casting over the Hawk/TBR7 as well. I have never had the Brozz and TT250 head side by side though to compare them.