Completely blown engine - Page 4 - Honda CBR250R Forum : Honda CBR 250 Forums
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post #31 of 35 Old 08-13-2015, 05:25 PM Thread Starter
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A couple of updates on my dealings with Ari. First, he's incredibly knowledgeable and helpful.

Second, the 300 engine does bolt directly to the 250 frame. But the 300 engine doesn't have a place for the O2 sensor, as that screws into the header pipe on the 300 (not into the header as does the 250). Most people who would do this change don't use the O2 sensor anyway, because they've replaced it with a PCV.

The 250 ECU will work with the 300 engine (although you'll need a PCV and a custom map).

Jett Tuning's custom PCV is the same for the 250 and the 300. So if you use Jett Tuning's PCV on your 250, it will work on the 300. I highly recommend it.

I don't have a complete list of parts for the 250/300 that are interchangeable, but it seems that most are identical, other than cams (different base lobe diameters), balance shaft, clutch hub and transmission.

Millenium Technologies in Wisconsin makes a bore kit for the 300. 78mm Wiseco Hi-comp piston. Increases the 300 to 300.8 cc (from the stock 286 cc). However, the 78mm Wiseco slug is made for the 250, so it has a much higher dome (and thus compression ratio) than is acceptable for the 300. You have to remove a lot of material from the piston dome to lower compression to a usable 13:1 in a 300 engine.

Ari has convinced me to stick with the CBR250 for racing. Even with a lot of work, it will never have as much top end speed or HP as a Ninja 300, R3 or RC390, but it handles better than any of them and with Ari's help I think I'll be able to get a new engine that is reliable (again, don't get the Takagawa) and can keep me close enough in the straights to pass again in the twistys
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post #32 of 35 Old 08-15-2015, 03:43 AM Thread Starter
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Final update, unless you let me know you want more info...

I get my new, fully race built engine delivered on Monday. Mount it on the bike, install a new map to my pcv, change the sprockets to adjust for more power and low end torque and, hopefully, race at Cresson next weekend! Still looking to show the ninjettes and duke 390s that the little Honda can go fast.

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post #33 of 35 Old 08-15-2015, 04:42 AM
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Nice one bro. Good luck on the track

Edit: Would you be willing to share your map data?

Take care & ride safe.

2012 Honda CBR 250RAb, Sold.
2013 CBR 600RR, Sold.
2013 Kawasaki Ninja 650R, Road. (wife's)
2015 Kawasaki Z300, Road. (wife's)
2014 BMW S1000RR HP4, Road / Flying Machine. (Traded in the wife for it)
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post #34 of 35 Old 08-15-2015, 10:19 AM Thread Starter
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Quote:
Originally Posted by midgeinc View Post
Would you be willing to share your map data?
Do you mean the actual map, or the dyno results? The map I'm going to use this weekend is from Ari and I would need to ask his permission. Probably wouldn't be much help anyway, since its for a heavily modified engine. And I won't have dyno results until I get my own map, which I plan to do in the next month.

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post #35 of 35 Old 08-15-2015, 12:31 PM
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No problem bro.

I was just interested to see the actual map. Mainly to see how different it is from my bike running with the Juicebox & full exhaust system. Mainly the deceleration values. If it is confidential. I totally understand. I still feel my map is a little lean on deceleration.

Take care & ride safe.

2012 Honda CBR 250RAb, Sold.
2013 CBR 600RR, Sold.
2013 Kawasaki Ninja 650R, Road. (wife's)
2015 Kawasaki Z300, Road. (wife's)
2014 BMW S1000RR HP4, Road / Flying Machine. (Traded in the wife for it)
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Last edited by tartan_warrior; 08-15-2015 at 12:51 PM. Reason: Grammer
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