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Discussion Starter #1 (Edited)
im going to say this now i have never modified a bike like this before

the inspiration 04 wr450f turned turbo lsr bike


im starting with a street legal 1986 honda xl250r


the turbo is a rhb31 good for 100 hp and is about perfectly sized for a 250cc engine
heres a small mockup before i decided to build a lsr bike


so far im still in the planning stages , and just today started to get serious about building this



and from here im going to just copy and past my post from the other forum

ok so heres were were at as u can see above the rear suspension lowers beautifully
some how i missed the step in my forks tubes si i couldnt drop the clamps all that far but i may not have to

u can see the step here

i was able to drop the clamps one inch


i can bore out the top clamp to go over the first step though if needed for about another 2.75 inches of drop but i really need a wheel and tire to figure that out as a 17 inch wheel will drop the front an additional 2.125 inches


centerline of the rear axle


centerline of the front axle with the 21 inch wheel


and from the rear footpeg mount ( lower craddle tube centerline ) is 7.25 inch from the ground


the front centerline of the same tube is 8.75 inches from the ground so a 2 inch drop at the front axle centerline should even the lower craddle tubes to almost paralell to the ground


bike deff needs a bunch of stretch for me to get on it comfotably in a layed over position


im thinking + 8 inches on the swingarm

and then cutting the rear subframe off tot he left of the right line and building my own , this will alow me to move the seat way back and let me lower the bike even more if i want to
 

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Going to be a bitch making jumps with that much rake.
 

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Discussion Starter #5
i had some time to mess with the bike , for my ideal seating position and to rear the bars i need to move the seat back 2-3 inches from were the rear of the stock xr seat is.
this will move a good percentage of my wieght above and behind the centerline of the rear axle , so it looks like im going to need atleast 8-9 inch extension on the rear swingarm

thoughts?
 

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Discussion Starter #7
notice anything wrong with this clutch stack ? this is how i pulled it out of the basket , had just a lil bit of clutch slip all last year lol


side shot of the clutch side of the engine

how the clutch stack should be , im going to end up turning my own bottom plate for the clutch stack so i can run a few more clutch discs
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and the twin carbs im doing blow threw on , going to try running this on e85 , or methanol of i can get jets big enough

piliot jet is removed from the primary carb already secondary carb only has a main jet


and does anyone know what this lil knob on the side of the carb is for ?? i played with it all last year made no difference in the bikes idle or how it ran
 

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Discussion Starter #8
gentelmen we have extension , or atleast a temporay one for mockup ( also swapped my stock 17inch rear wheel for an 18 inch wheel off an xr200r i had laying around )



lol couple changes to the suspension and i can do lsr/drag, and hill climbs lol
 

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Discussion Starter #9
so heres how im thinking about dong the rear section of the bike , red lines are what im adding , and blue line at the back is just an extension of whats already there so i can move the seat and fender back
tieing all in to the swingarm should take all the flex out of the frame since im doing a rigid rear suspension

 

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Discussion Starter #10
mocked up some more stuff today




im going to possibly slide the battery forward and that leaves me enough room infront of the rear tire to build the fuel tank instead of putting the tank uptop on the top tube , not sure were im going to put it yet though



 

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Just remember...width is wind resistance just as height is...You planning on running it with fairings or naked? I miss land speed racing. If you want to get really inspired and depressed at the same time..Look up Hass/Serafini racing. Good friends of mine chasing the 300 mph record in 1.5 miles. Looking forward to more man. Ive often thought about throwing a bike together to race but I have other stuff on my plate
 

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Discussion Starter #12
Just remember...width is wind resistance just as height is...You planning on running it with fairings or naked? I miss land speed racing. If you want to get really inspired and depressed at the same time..Look up Hass/Serafini racing. Good friends of mine chasing the 300 mph record in 1.5 miles. Looking forward to more man. Ive often thought about throwing a bike together to race but I have other stuff on my plate
probably naked this year , maybe a lil windscreen or something to get my head/helmet behind , gota read the rule book again and see what all i can do
 

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Discussion Starter #14
cool deal man. Cant wait to see more..it already looks better, longer, and without the seat and tank haha
just mocking everythign up till i have the bike just about done so i can make sure everything is good before i weld up the frame/swingarm , turbo kit etc etc incase i need to change anything , once its all mocked up and together and i know its how i want it ill do all the final fab and welding

stock seat and tank are deffinatly getting tossed , part of me wants to pick up 2 2.5 pound nitrous bottles and make the fuel tank out of them
 

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Just like in Off roading, keep weight low, and balanced. the nitrous bottles isnt a bad idea, depending on how much you plan to ride it, I think one would be sufficient, we ran a 5 gallon moon tank on one of the cars I was racing and with a healthy small block, we burned maybe a gallon with warm up, and the run (short or long course) on the salt... While weight isnt a penalty per say on the salt, with a small displacement like your bike, it will be in my opinion. Remember the racing mottos

"Every ounce counts" "nothings lighter than a hole" and "is it breaks, make it stronger, if not...make it lighter"

haha. Im pretty stoked on this project man...Its gonna be fun, different enough to be noticed and you wont be into it a bunch initially....until the bug bites hard and you go insane
 

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Discussion Starter #16
....until the bug bites hard and you go insane
oh im already eyeballing the almost 50hp motor off the kx250f i just bought , the only problem is its 13.5-1 cr stock , a 10-1cr piston and the turbo and that thing would be a screamer . but i just bought the bike so its not going to happen the kx didnt come cheap lol

there is however is a 440cc snowmobile engine laying around lmfao
 

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Discussion Starter #18
Old Turbo 2 cyl bikes needed a "surge tank", curious if one will be required here.

Cool project!!
thanks

are u talking about the oversized plenum before the carbs? if so i have made mine a lil to big , but ive seen some videos of what happens when when its to small or not there at all so i purposly made it a lil bigger
 

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Discussion Starter #19 (Edited)
turns out my 1mm oversized forged piston puts me out of the 250cc class and into the 350cc class , so i need to see if i can press the pin out of my stock piston without damaging my piston but i have a feeling its not going to work out , if i get stuck using my oversized piston , ill use the stroker crank as well and push the motor to 273cc and run it in the 350cc class for fun

looks like im going to be in m/pbg or m/pbf if i run methanol possibly could fit into m/vbg(f)
 

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oh im already eyeballing the almost 50hp motor off the kx250f i just bought , the only problem is its 13.5-1 cr stock , a 10-1cr piston and the turbo and that thing would be a screamer . but i just bought the bike so its not going to happen the kx didnt come cheap lol

there is however is a 440cc snowmobile engine laying around lmfao

turbo sled motor sounds fun....imagine the linear with the clutch set up properly...and being a bunch lighter than the sled will help...only downfall is the width
 
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