Performance cbr250r

I don't know, but if you have a competent machine shop and know how to assemble and disassemble engines yourself, and can find a way to change the ECU (should be coming in the next year or so from some aftermarket guys) to allow a higher redline, you should be able to bump the baby CBR up from 25 hp give or take to around 40 hp.

The procedure would be relatively simple. Given that the bike shares the cylinder characteristics (bore, stroke, valve size, etc) as the CBR1000r, but differs in compression (and I think, redline). The first order of business is to bump compression by having a small bit of the mating surface between the head and the cylinder sleeve (block?). The goal is to bump it to around 12 to 1 or 12.5 to 1 from the stock 10.5 to 1 ratio. While the head is off and disassembled, porting the intake and exhaust ports would be fairly easy as well. When the engine is re-assembled the cams could be adjusted for a bit of overlap (exhaust valve stays open a for a short moment as the intake valve opens thus creating a suction effect). If aftermarket cams are ever made available, then would be the appropriate time to install them, along with stronger valve springs.

With the internal work done, the next step should be to remove restriction in the intake and exhaust areas. Given that we would likewise increase the redline and be shifting the powerband upwards in the RPM range, a free-flow exhaust and intake would be helpful (where if we kept the stock trim and wanted lots of low end power, the free flowing exhaust would cause losses in the lower RPM ranges). The pipe should be something light and with a straight-through design, if not a straight pipe. You gain the added power, as well as losing the weight of the stock piece. On the intake side, sourcing a larger throttle body and working with the airbox would net a small gain in power.

After all the physical modifications were completed, the bike's ECU should be tuned for a higher redline and for a bit richer fuel map to make the most of the higher airflow and higher compression without detonation.

I can't promise the bike will sound like a champ, but it should be very quick with those modifications.

Once I own my bike (paid off- no more Honda Financing), and I have relegated it to something less than a commuter (just for fun bike likely, or a partner bike to a future 675 Daytona and KLR650) as well as when my 5 years of warranty is expired, I plan on doing those modifications as well as tuning the suspension more thoroughly and adjusting the ergonomics to make it more aggressive for track days and aggressive back-road riding.

No disrespect but you're not going to take this 25hp motor and turn 40hp with it. That's a 60% increase in hp and not just realistic unfortunately.

The Ninja 250s 2007 and previous were making approx 27-29hp and with pipes, jetting, K&N or pods, and high compression pistons, none of those bikes were making more than 33-35hp. And that ons a twin cylinder that's already starting with more power than the CBR250.

The CB250 engine despite its decent design, is going to reach it's normally aspirated limits somewhere around 30hp and that will be a healthy increase that will be really felt as singles develop such good torque.

Just to give you an idea the CRF230 engine totally modified out by a Factory Honda Racer (former) at 251cc, high compression piston, porting, high perf camshaft, larger valves, exhaust and everything imaginable is just breaking 30hp I believe Mike is claiming around 32hp for a single cyl 250 that's amazing! He's spent prob 5 years developing this engine...

You could possibly see 40hp if you were running alcohol, with all the other mods, and super high compression ie: 14:1 or higher with the timing adjusted appropriately - and we're not talking pump gas alcohol we're talking cart racing methanol that burns twice as much as pump gas, giant jets, wide open only... which would be good for the Maxton Mile to try and set a 250cc record for single cylinder four stroke...

Great little engines they just aren't made for peak power they are made to be torquey...

Mike

Lee I think these little bikes are more giggle per cc than the bigger bikes! I mean screaming around town makes you feel like you're road racing just when you're headed up to Circle K for a loaf of bread! *grin*

I'm a fanatic about the 250 bikes as well. Love the 250cc Ninja and was headed for a land speed record when someone went far beyond my bank account so that pretty much put an end to that - though I'm tempted to see what rules they have at Maxton to see if I can still pull something off.

The CBR250 being a single is quite exciting. Until now the most exciting 250cc engines I can think of are the XR motors, and actually the performance that the companies built for the XR200 might surpass the XR250 performance. Roller bearing cams, or cams in bronze bushings etc, etc... so this new valve train which is actually an old valve train which was proven on the CRF250 is exciting. It puts new possibilities into the 250cc single class...

One thing that's awesome about big singles is the amount of "thump" you get out of them. Just got done building a 680cc XR650 that is totally tricked out - it's a rocket for a big single and more fun than should be allowed on the street.

I'm dying to play with the CBR250 more than just the test rides from working at a Honda dealership. After having played so much with Ninja 250s I see some quick/easy performance upgrades for this little rocket which is exciting...

Mike

I understand you meant no disrespect, and none was taken.

As I have said before, and I will probably say again, the CBR250 and Ninja250 are completely different in the way they will make power from modification. The Ninja already comes with a 12.5 to 1 compression ratio and a 12.5k redline. While it does lack some of the technological advancements (at least in stock USDM form) of the CBR, those two features alone allow the bike to put down more power in stock form.

Basically, the way the two bikes respond to tuning will be completely different. Tuning a CBR involves making advancements in power that were stock on the Ninja. Milling the head and/or installing a higher compression piston along with tuning the ECU to apply the appropriate amount of fuel for the higher compression ratio as well as raising the redline to 12.5k rpm puts the bike on equal footing technologically with the Ninja. Just a guess, but I would say that it would make similar power, likely in the high 20s low 30s range.

From this point, equal gains should be possible. Increase the size of the injector to match the CBR1000rr's injectors. Find aftermarket cams and adjust timing. Find a free flowing intake and exhaust, and install a slightly larger throttle-body. Tune accordingly. I would estimate a conservative 30-35bhp from all mods in total.

My initial 40bhp range may have been a bit out of reach, however, I see two examples why it is not entirely unreasonable.

The first is the production CBR1000rr, which shares the same bore, stroke, and valve diameter as the 250r's single cylinder. Conservatively, the 1000rr is making 160 hp, so naturally, one quarter of that would be 40 hp. I know there are other factors at play with a multi-cylinder engine, but it was a gross estimate.

The second example is the new Honda Moto3 race bike, the NSF250r, which features a single cylinder, four stroke, 250cc motor. The measured power on this bike is between 47 and 48 hp at 13k rpm. With a milder street tune, running on pump gas, 35-40 hp seems about right.

But lets be honest, anyone looking for a faster street bike isn't going to dump 5 grand into a 250 CBR or Ninja to make power, when they can sell the bike for 3k and take their 5k and buy a new 600cc or used liter-bike. Well, the only people I could see doing that are people who would want to use the bike for track days to learn on without buying a 600cc, and even then it would be easier to just step up to the bigger bike (I know I will, already eying the 675 Daytona), but it would still be interesting to see someone with a lot of disposable income take the CBR250 to its maximum performance capabilities.