Jump to content

250R motor in 150RB frame?


Recommended Posts

Sorry if this is a repeat post. I searched but didn't didn't find another post on this but thought I had read something along these lines a while back.

Anyway, I'm talking to Service Honda about buying a 150R with a 250R motor installed (I'm wanting more from my 15OR). Has anyone had first hand experience with these bikes? I have read where people have done this conversion, but I can't seem to find how the results actually performed.

Also, what's everyones opinion for doing this, versus sinking $1,500 or so into my current motor? I've always been hesitant towards pushing the limits of a motor because it seems like you really limit the life of the motor as well as sacrifice dependability.

My current 150R is pretty much stock. It has the quick shot fuel accelerator pump and Yosh silencer. I dropped down to the 150 from a 250R due to being too short to ride trails. I still ride motocross but also ride trails and am just looking to get more power out of my 150R. I think a 250R motor in that chasis would be sweet...... but I also haven't heard back on what it will all cost yet. Should be getting a call later today with the numbers.

What's everyone's thoughts?

Link to comment
Share on other sites

Im not sure you would be happy with my thoughts. As for the performance, I would just think that is too much for the size of that frame and those wheels. This is just my opinion, but I am pretty sure a 250 will go anywhere that will.

I completely respect your thought..... and I can't say that I disagree, but I'd sure like to try one out. I think it might be a lot of fun for a short fat guy that can't touch the ground on a full size bike. But I'm also not sure it would be worth the money. BTW - where abouts in Idaho are you locate? I'm about 20 miles north of Moscow (university of Idaho).

Link to comment
Share on other sites

I own a service honda jr r. its a great bike. but there are issues that need to be addressed in the handling department if you truely want to unlock the potential of this bike. For starters, it is the funnest bike you will ever ride...period. But the swingarm is two short for the added power, and the front brake does little to slow the freight train down. I added two inches to the rear of my swingarm, and got an oversized disc. I also added a fox shock to help with the added weight (the stock suspension is setup for someone more in the 130ish range.) when you add the added leverage of the longer swingarm, a new shock is a must! (im 165lbs, and the shock says its good for riders up to about 185lbs on the stock swingarm) Service honda actaully does a pretty good job with the thought process of the build (adding extra bearings in the swingarm for the added weight etc...) But some of thier welds do leave something to be desired. I have about 40 hours on mine (its the fun stepchild to my big bike). i have had mine for about two years now. If your serious I have been giving some thought as to selling mine(no hurry, just been kicking around the idea). Due to only riding it 40 hrs in two years). 35 of the hours where in the first year. It has many upgrades. Pm me if your serious! If not I hope that some of this info helps out your decision either way

Tom

Link to comment
Share on other sites

I'm not really sure what all the options are. I know yamaha makes a 1.5" lower kit that I think is just different linkage. But i'm not sure 1.5" is going to be enough on thee trails, and I'm also not sure what affect this has on the suspension. I ride motocross as well and would have to limit my rear suspension. But like I said, I don't know what all options are out there for lowering a full size bike. It's definitely an option.

Link to comment
Share on other sites

I agree with those who think you'd have an unbalanced machine. A good portion of the 250R's power would be wasted with the small wheels, short wheelbase, short peg-to-bars distance, etc.

The 150R makes very good power....what makes you feel you need more??

Perhaps increased rider skill/decreased rider weight (­čśĆ) would be viable alternatives??? Be a lot cheaper, AND result in a much more durable machine and rider (you'll crash less often and live a lot longer).

Sounds like I'm preaching, but all too often we look to throw money at a problem that could be cured by better means...even if the money solution is much less effort. ­čśĆ

Link to comment
Share on other sites

I would big bore the 150 first

stock

150RB%20stock.jpg

O 170cc 12.8:1 big bore kit, EO RD valve springs with Titanium retainers, EO Megacycle billet cam, EO Steahly off road 7oz. flywheel weight, EO Tokyo Mods carb modification, EO slotted cam sprocket. 91 Octane pump gas.

CRF150R2694.jpg

  • Helpful 1
Link to comment
Share on other sites

Ok so I did some searching and the 250 engine is listed at 52.7lbs and the 150 at 43.6lbs. So roughly you will be adding 10 pounds to the CRF150RB, which lists at 183lbs on Honda's web site. So with some heavier engine mounts etc. you are looking at about 195lbs. Well the CRF250R is listed at about 215lbs complete with full sized wheels, bigger tank etc... Now I like a 20lb difference and one thing to consider is the power curve of the bigger engine. Here is an overlay of a 250R dyno run on top of the previously shown dyno chart for the 170cc engine. The Red line is the stock CRF250 and the top line is the same engine with an Akro exhaust. These were taken from the posted/corrected Dirt Bike exhaust dyno runs.

CRF150vs250.jpg

Here you can see the really strong bottom end performance of the stock 250 engine when compared to the tricked out 170cc/150 engine. Peak power isn't far from different, but lots of difference in the lower part of the powerband. This would make a supernice trail bike engine in the smaller frame. Of course you could also mount bigger wheels onto the RB which would still be smaller and lighter than the stock CRF250 by probably about 10+lbs....

Is it worth it? You have to decide! Who does the work and how much does the finished bike cost? You could always put more than just the aftermarket exhaust onto the 250, make it a 270 or 280? Loads of fun!

Remember that dyno runs on different dynos are not accurately comparable so this is for general reference only.

Swiss

Link to comment
Share on other sites

Not to hijack your thread- But I've been acquiring CRF150R part for some time now, for a custom build (already have a few custom builds under my belt - CR85RB/XR100, CR500AFC) I've considered a few different power plants (larger than the XR100) XR200, DRZ/SP/DR 125-200 (potential to make +225cc and +20hp). Estimating the cost involved in building a Big HP air cooled thumper- the CRF250R engine is/was looking a little more attractive with deep pockets....

I'd Like to keep this/my 150R conversion budget friendly and started to consider a 2 stroke engine- ala-KTM 200 or KDX200-220. Relatively inexpensive, good HP potential, light weight, and supper easy maintenance! Than again- I have a spare 04' CR250R motor lol

Link to comment
Share on other sites

I have a 150R big wheel rolling frame and want to do the same thing. I am short and tried everything to make my 250x work but in the end I traded for a 150 r and the motor blew up. What kind of money are we talking about to have a 250r installed?? I also like the 2 stroke option if anyone has thoughts on that.

Link to comment
Share on other sites

I have a 150R big wheel rolling frame and want to do the same thing. I am short and tried everything to make my 250x work but in the end I traded for a 150 r and the motor blew up. What kind of money are we talking about to have a 250r installed?? I also like the 2 stroke option if anyone has thoughts on that.

Besides the obvious of just rebuilding the motor, you can give DMC a call about putting a two-stroke motor in it. What's nice about him doing it is he can make the motor pretty much do what you want and the bike comes out factory looking.

Link to comment
Share on other sites

Besides the obvious of just rebuilding the motor, you can give DMC a call about putting a two-stroke motor in it. What's nice about him doing it is he can make the motor pretty much do what you want and the bike comes out factory looking.

do have a phone # for DMC?

Link to comment
Share on other sites

You want more, flexible power...why limit yourself to the 250 engine?? For a few pounds (and a few dollars) more, you could have a Honda 450R engine in that little puppy. Then, you wouldn't have to worry about adding "power enhancers". :banana:

It's virtually the same size as the 250......

Link to comment
Share on other sites

  • 3 weeks later...

if a manufacturer puts a motor in a race bike it is maxed out

u couldve lowered the 250 or u can put a 175 cc bigbore kit in the 150

idk if the 150 frame could take the added weight of the 250 motor and the extra motor space

really if u play with the sprockets and bought really cheap (extremely cheap crappy ones) ones u could get a lot more power i race the 150 rb in hairscramble and when i want more power it gives it

ur tires has a lot to do with the power to the ground

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

├Ś
├Ś
  • Create New...