Crf150rb w/ 450x motor?

I seen online a guy made a crf250jr, i was thinking crf450jx would be the bees knees! If im gonna commit to this build, i wanna go big not goin home! electric start 40+hp and convert to road legal. well at least look legal on paper:) I am an excellent tig weldor and fabricator. curious...how much bigger and heavier is the 450 over the 250 and 150? Im a small guy and miss my old kx100. I want the meanest way too powerful trench digger i can make yet a still functional bike.... And fuel injection would make this little bike about the coolest thing i could think of. The only problem i can foresee would be that for one i would have to offset the motor for sprocket chain alignment and two might have to raise the back bone to clear the swing arm pivot point/ chain slider and valve cover clearance to frame???

What do yall think? Possible?

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Even if all this works, your "still functional bike" statement would be thrown out the window. People that have the Service Honda bikes talk about too much power for the size frame. Add in the extra HP of the 450 and I bet the bike will be un-ride-able! If this is what you want go for a KTM150 frame to start.

Hot Rod Magazine's perennial fool, Stroker McGurk, used to say, "If some is good, more is better, and too much is just enough." 

I would bet if this 450x motor could get traction, the frame would fold!

I would bet if this 450x motor could get traction, the frame would fold!

 

+1 on this. With all the welds? Yeah!

 

I like frankenbikes that work, but this CRF150RB/CRF450x hybrid is not likely to ever be one of them.

 

The CRF frame is so small you'd have to cut and stretch the backbone, downtube and cradle. Then you'd need a custom fabbed tank to accommodate the fuel pump. Then there's the short wheelbase and small wheels. Also, there's no room for the battery and ECU, except in the airbox, and the airbox is too small for the 450 anyway, and there's no room for a bigger one. And on and on....

 

Like you said, might as well start with a 125 sized steel frame like on the newer KTMs. If you wanted any chance at all of ever having the front wheel on the ground under acceleration, you'd need the extra wheelbase anyway.  

 

If I were going to build a big motor into a CRF150RB, I would try a Husky 310, fitted with an FCR carb, maybe even the one from the 150 (to detune it enough to make it manageable). From looking at it, it seems smaller and lighter even than the CRF250R engine, and makes plenty of power. Still have to do a lot of butchery on the frame and extend the swingarm though. Oh, and geek out an interface between the TPS and the ignition module. Kickstart's worked fine on every dirt bike I've ever ridden.

 

Actually, KTM has already built a bike that fits the profile we're talking about: the Freeride 350 (which is soon to be available in the US). It uses the forks and shock from the 85/105, the engine from the EXC 350 (but with SS valves rather than Ti). It is choked by a smaller injector and very restricted exhaust, but has the same head and cams as the EXC. At 220lbs it is a little heavy. But Yoram Lavee rode one in this year's Romaniacs, and was doing very well (close to top 10 in his class) until a fall broke his wrist on the last day. He did a few essential mods to his bike: see http://www.y-fr.net

Edited by Old Plonker

Hot Rod Magazine's perennial fool, Stroker McGurk, used to say, "If some is good, more is better, and too much is just enough."

I want that retarded insane powerrrr! I have a 1989 crx hf that came with 72 measly little ponies, and its been handling the new 312 whp k24 supercharged swap fine for 3 years now.

My point is honda makes stuff right to begin with and us americans love to take it to the extreme, if you build stuff right they can last for a good while.

Okay your right.... F the button start. Maybe a crf450r case and 450x top end for better longevity?? No FI (your right about the fuel pump issue). Carbed model w/ hose clamp style uni filter. Maybe a 2in longer swing arm. Stronger springs, sink the forks a lil?

You can make turbo hyabusa's ridable...

Thinkin a deff throttle stop some how so i can have a chill mode for when im not feeling too froggy??? Maybe on the fly???

Interesting: a blown K24 in an HF. What a sleeper! If you have the chops to build and debug that ride, then a vest-pocket CRF450R/X is doable.

 

The thing with the CRF150R is that the frame is not that light and space is really tight the way they laid it out. You would probably do better to fixture the engine, radiators, forks, swingarm, shock, tank, seat and pegs, and wrap your own frame around them, leaving room in the right places for airbox and other finishing ancillaries. Take the layout of the rider ergos from a proven bike of this size (the XR200R is one of the best, in my opinion). For that much power, you'll want at least 53.5" wheelbase, and another inch wouldn't hurt. You could probably use a CRF125 swingarm to get there.

 

With the right layout you could switch between 16"/19" and 18"/21" wheels, depending on the type of riding you are doing. Heck, you might even keep a set of 17" motard wheels around for tearing up the asphalt! 

 

I like the idea of SS valves and a milder cam for longevity and rideability, and the chill mode (switchable ignition retard?) would be a life saver at the end of a long ride, when you're dehydrated and your coordination is running about 300 milliseconds behind your intention, and a get-off is just a twitch of the throttle hand away.

 

Dang, maybe you really will build this monster! But the image I get is that it would be more like if you had a built 400 cube small block in the back seat of your HF! Fun, but maybe not so practical as the blown K24 up front.

Edited by Old Plonker

And shes ugly tooImageUploadedByThumper Talk1377601043.972169.jpg

I like wicked speed,14' flat bottom aluminum jon kawi 750(760cc now +1mm bore)90hp ski engine. 300lbs 47mph ImageUploadedByThumper Talk1377602563.710544.jpgImageUploadedByThumper Talk1377601295.176302.jpg

And shes ugly tooImageUploadedByThumper Talk1377601043.972169.jpg

I like wicked speed,14' flat bottom aluminum jon kawi 750(760cc now +1mm bore)90hp ski engine. 300lbs 47mph ImageUploadedByThumper Talk1377602563.710544.jpgImageUploadedByThumper Talk1377601295.176302.jpg

I like that, you dont know that its fast until your eating my roost:p

Interesting: a blown K24 in an HF. What a sleeper! If you have the chops to build and debug that ride, then a vest-pocket CRF450R/X is doable.

 

The thing with the CRF150R is that the frame is not that light and space is really tight the way they laid it out. You would probably do better to fixture the engine, radiators, forks, swingarm, shock, tank, seat and pegs, and wrap your own frame around them, leaving room in the right places for airbox and other finishing ancillaries. Take the layout of the rider ergos from a proven bike of this size (the XR200R is one of the best, in my opinion). For that much power, you'll want at least 53.5" wheelbase, and another inch wouldn't hurt. You could probably use a CRF125 swingarm to get there.

 

With the right layout you could switch between 16"/19" and 18"/21" wheels, depending on the type of riding you are doing. Heck, you might even keep a set of 17" motard wheels around for tearing up the asphalt! 

 

I like the idea of SS valves and a milder cam for longevity and rideability, and the chill mode (switchable ignition retard?) would be a life saver at the end of a long ride, when you're dehydrated and your coordination is running about 300 milliseconds behind your intention, and a get-off is just a twitch of the throttle hand away.

 

Dang, maybe you really will build this monster! But the image I get is that it would be more like if you had a built 400 cube small block in the back seat of your HF! Fun, but maybe not so practical as the blown K24 up front.

If you stretched it, add bigger wheels, will it still be a mini?? Fun factor would be a big motor in a small frame. However to build a frame for this 450 motor and have it be ride-able would put it in a 150/200 2t non-mini chassis! A lot of work just to hurt yourself!:)

If you stretched it, add bigger wheels, will it still be a mini?? Fun factor would be a big motor in a small frame. However to build a frame for this 450 motor and have it be ride-able would put it in a 150/200 2t non-mini chassis! A lot of work just to hurt yourself! :)

 

I think the only reason one would build a bike like this is to say, "I've done it!" There aren't a lot of riders that can fully exploit the power of a full-sized 450 on the MX track. In a mini chassis, it's just nuts. But sometimes we do nutty things just because we can. The OP seems to be that kind of guy. I say, if he has the skills to do it, more power (pun) to him. 

I have an Oldsmobile 455 in the back seat of a '69 Opel GT.  Is that overboard enough for you.  Have taken it around the block but need more work to finish and add A-C and Cruise-Control and a nice stereo for the open road!  When you build them right they sometimes turn out a little Radical!

Think a buck 30 would be a little scary on a 150???

Think a buck 30 would be a little scary on a 150???

Stupid app keeps posting twice!

I have an Oldsmobile 455 in the back seat of a '69 Opel GT.  Is that overboard enough for you.  Have taken it around the block but need more work to finish and add A-C and Cruise-Control and a nice stereo for the open road!  When you build them right they sometimes turn out a little Radical!

 

Swiss,

 

I'd love to see pictures of your GT and hear what you did for the transmission and rear suspension. Sometimes too much is just enough!

Think a buck 30 would be a little scary on a 150???

 

I think I'd need a change of shorts.

Edited by Old Plonker

AS a person who's been into conversions for going on 25 years, it's wayyyy different than a car, unless you want to drag race it maybe.  But as a motocross bike  it just wouldn't be that functional.  Cool yes, functional no.  I beat a guy on a 250f converted CR85 and I'm not even that fast.  (then, now I'm even slower)  It sounded like a 450 behind me, I didn't know what it was.  But I was on my XR150/CR85 with maybe 12 hp.  He had me by at least 28 hp.  Point being he couldn't use it.  It was the old stadium track at Glen Helen and not the main track, but still with that much power, you would think he would smoke me.  99% of all riders can't use the power of a 450 in a 450 frame, so stuffing it into a 150 frame would be that much worse.  It's just the whole geometry of everything, the weight, placement of the motor, the front sprocket, things like that.  Plus, I've had some scary moments on my 150 where it just wants to huck you off going down a straight for no particular reason.  I couldn't even imagine that with a 450 motor.  It would be like Roczen's crash at Millville only with a 450 motor.  OUCH!!!!   Anyway, to do it just to do it would be a fun project and really cool, especially if it comes out super sano. 

Perfect:)

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