cbr250rr modifications

**mossy1200** · 10th October 2009, 21:56

A 15-20% gain in top end horspower is going to cost you head work ,cams,higher compression and flatslides and pods.Are you prepared to put in 4grand to get 10hp?
Bearing in mind this will also cost you mid range hp and torque.

Cheeper to get bigger bike or sell and buy rs250 aprilia if your on licence restriction.Maybe get a race bike and live with the road power you already have.

**Dave-** · 10th October 2009, 22:00

I'll vouch for the 44RWHP claim

I've seen the print out!

BUT eliots gixxer did only score 103 when it should be up around 115, however I think jeff may have had it dyno tuned to run 1/4 mile, as I remember he use to do drags.

**Bangbug** · 10th October 2009, 22:24

you can be brave and advance the timing 3 degrees and run it forever on 98.
They retarded the timing through the midrange from the factory.
NOBODY can make an after market ICU for them cuz they rev too hard, lol.
Give the carbs an overhaul. (take it to a tuner) (ok... a good one)
Give the suspension an overhaul.
Buy some STICKY tyres.
Buy some QMOTO gear.
Buy some brave pills

**Spyke** · 11th October 2009, 11:14

I saw on the net a 250 bandit with turbo making alot of hp did a 12. something down the quater.

I saw that on the net though

**SS90** · 11th October 2009, 20:32

Originally Posted by Spyke

I saw on the net a 250 bandit with turbo making alot of hp did a 12. something down the quater.

I saw that on the net though

Then it MUST be true.

**The Pastor** · 12th October 2009, 09:28

Originally Posted by Bangbug

you can be brave and advance the timing 3 degrees and run it forever on 98.

Care to explain this a bit better? What dose advancing the timing do? any other mods that have to to with it? what improvement does it offer?

Thanks,
Rm

**Dave-** · 12th October 2009, 10:01

Originally Posted by renegade master

Care to explain this a bit better? What dose advancing the timing do? any other mods that have to to with it? what improvement does it offer?

Thanks,
Rm

fuel takes time to ignite and start expanding.

when the spark fires the expansion isn't instant, there's a measurable number of milliseconds before it starts happening.

iirc (and feel free to correct me if im wrong) factory bikes are tuned to light the spark when the piston is at its highest point, so when the fuel starts expanding the piston has started going down already, this loses valuable time that the piston could be pushed down, instead it's just bring pulled down thanks to the crank.

what you can do is make it so that the spark fires before the piston gets to its highest point, and time it (hence ignition timing) so that the gas starts expanding the instant the piston is at its highest point.

however this will lead to more engine wear, if you fuck it up and expand before the piston reaches it's highest point you'll blow your bearings, you'll also want to use a very fast burning fuel (98 octane)

do what you want, but if you blow up your bike, not my fault.

**vtec** · 12th October 2009, 10:38

Hmm, you are mostly right, but I'm pretty sure that higher octane is slower burning which is why you need to use it when you have a lot of timing advance, so even if it explodes before TDC it is slightly slower to start pushing the piston down.

If you don't want to fuck with the timing then just do what I do run it on 91 octane as that is what the timing is set up for. There probably is a bit of power to be gained by doing the 3 degree advance and running 98, but it comes with a big risk. I would probably be more inclined to do a 1 degree advance and try running it on 98 and 91 to see which one behaves better.

These engines going extremely fast actually suit the lower octane and have a designed retard to run it safely, as it explodes quicker than 98.

I can be sure there will be arguments about this.

i'm sticking with track time and good tyres. Just make sure the fork oil is relatively fresh too.

P.S. Thought of another way to put the advance problem into words. You can only tune the advance to suit one part of the rev range if you don't have Honda's VTEC system or Toyotas VVT... or any VVT system, so if you tune it to suit the most powerful part of the rev range, then you will have issues with detonation at lower revs (a bad thing). I vote for leave it the hell alone and get a faster bike if you want more power. TheCBR250RR is the best 250 IL4 largely because of its reliability, change anything more than flow and fueling and I guarantee you will lose reliability unless it is done by an excellent engineer.

**BladeBoy** · 12th October 2009, 17:18

thanks for all of your input guys. i think ill just upgrade aye. might be easier. moneys a bit tight but i see a might be able to sell mine and get a vfr400 for not much more money . do they have much more power? id prefer a cbr600 or r6 but to expensive at the mo with baby number 2 on the way.

**mossy1200** · 12th October 2009, 17:26

Originally Posted by BladeBoy

thanks for all of your input guys. i think ill just upgrade aye. might be easier. moneys a bit tight but i see a might be able to sell mine and get a vfr400 for not much more money . do they have much more power? id prefer a cbr600 or r6 but to expensive at the mo with baby number 2 on the way.

Vfr is nice bike.Not huge power increase top end but lots more torque through the whole range.250s sell for good money if your not rushing a sale and not big price differnce to a 400.If you want lots more power then 600 would be the go but a good 600 is going to cost 5grand upwards.Most older 600s are flogged and worn out unless you get lucky with your search.

**quickbuck** · 12th October 2009, 17:48

Originally Posted by mossy1200

Most older 600s are flogged and worn out unless you get lucky with your search.

Ahemmmm.. I wouldn't say it is flogged out.... much.....
Still does rapid times arounf Manfeild..
Then again, check vtec's first post for "Tuning Advise"....

**mossy1200** · 12th October 2009, 17:54

Originally Posted by quickbuck

Ahemmmm.. I wouldn't say it is flogged out.... much.....
Still does rapid times arounf Manfeild..
Then again, check vtec's first post for "Tuning Advise"....

Unlike 99% of 600 owners of late 80s early 90s bike you would know where the sump plug is and the oil you give it is called an oil change not top up.

**.produKt** · 22nd April 2010, 17:20

De-baffling the airbox is something i've heard. Anyone care to testify?

**ac3_snow** · 30th April 2010, 00:39

Hey mate check this out re your airbox
http://www.cbr250.com/cbr250/forum/t...TOPIC_ID=26849

all Iv done is replace my filter with foam (uni foam from most mtrbike shops-remember foam oil too) and noticed a slight improvement (then again old paper 1 was filthy). didnt reali have the time or funds to get right in there with new jets and all.
Interesting looking at the dyno sheet someone showed previously tho makes me wanna strip my carbs and clean etc....
I have heard that the headers where sumwhat restricitve too, but for the cost of new ones is it reali worth it?
that cbr250.com site has some wicked tech posts and tips (saved me when i stripped my brakes down) shows you how to do fork oil and stiffen them up etc..