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sofadriver

uberfast KX100

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I am building the next version of my KX100 powered bike to set a new Land Speed record at the Bonneville salt flats. I had a well respected builder do the motor with mediocre results so I am NOT looking for the name of another "2 stroke guru". So heres my question - if you had to build a KX100 motor to go as fast as possible at wide open throttle for 3 miles (multiple times) without blowing up, what would you do to it? My cooling system is excellent so thats not a worry. It must pull past 13k rpm. Thanks in advance

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Kind of an extreme request.

Balance crank, have all your specs perfect, jet for 18:1, fine ways to remove rotating weight. Flywheel in a lathe? Cnc holes around all the gears In the bottom end, micropolish tranny. Get a really radical porting job done, stack base gaskets to raise ports then use a stroker crank and head milling to get really good compression.

Just spitballing here

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^Good tips. Making a fast machine is never from one big solution, it's many many many small solutions. Speed records? Even respectable speeds? Big $$$ will be going into this. 

 

Extreme gearing, custom exhaust, street tires/slicks, remove all unnecessary weight, and get your drag coefficient down. Do you want it to still look like a dirt bike? I doubt it will be breaking any speed records if so. Get rid of the plastics, make a custom fairing that will just about enclose the lightest rider you can find. 

 

As for the motor, we're always going to refer you to our 2 stroke gurus, and even still, they won't nail it on the first try. There's always more to try.

 

What does the bike look like now? (pics please)

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I am building the next version of my KX100 powered bike to set a new Land Speed record at the Bonneville salt flats.

 

The current land speed record is over 763 mph. I doubt anything you do to a KX100 motor will allow you to go that speed.

 

http://en.wikipedia.org/wiki/Land_speed_record#Records

 

Or 394 mph if you are talking specifically motorcycles.

 

I think anything much over 125mph will be difficult to obtain with a KX100.

Edited by woods-rider

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Kind of an extreme request.

Balance crank, have all your specs perfect, jet for 18:1, fine ways to remove rotating weight. Flywheel in a lathe? Cnc holes around all the gears In the bottom end, micropolish tranny. Get a really radical porting job done, stack base gaskets to raise ports then use a stroker crank and head milling to get really good compression.

Just spitballing here

 

+ bigger carb, custom pipe

 

I think it'd be worth altering the bore and stroke to suit that kind of RPM.  The kx100 is already a punched out 85 motor, so I don't know how much bigger it can be bored without affecting the integrity of the cylinder.  Assuming you can go bigger, you would want to increase the bore to the limit and shorten the stroke as much as is needed to meet the displacement requirement.  The result is reduced reciprocating loads in the bottom end and reduced thrust loading on the piston skirt.  This would require extensive cylinder modification in addition to a custom crank to achieve the correct port timing but you were probably going to have to do that anyway.

 

Option number two is a destroked 125cc motor.  A 54mm bore with a 43.5mm stroke comes out to 99.57cc's.  This requires a similar amount of crank and cylinder modification but the 125 ports would be much closer to where they need to be for 100cc displacement and 13000 RPM.  The 125 bottom end is also much more robust than the 85/100 bottom end.

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Ceramic bearings all around, balance the tires. Lots of oil in your mix and jet the main really heavy. Really your going to want the best fluids you can get.

Biggest water pump you can get your hands on.

You may also want to look into the lightest weight piston you can find.

I would think maybe try and find a CDI box where you can get different ignition curves would also be a must.

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Thanks for the input, guys. No pics since new frame is just being mocked up. Forward vision will be over the top of a 24" race slick and under the lower fork tree (eyes at about 26"). Motor is being used because its under 100cc and has a 6 speed w robust clutch. Version. One ran over 120 on the street but that wasnt on salt and wasnt at 4200'. Thats the unique thing about running at Bonneville.- you never really know and theres only a few days to get it right. 10" of water from a freak storm this year. Over 500 teams went home dissapointed. Me included. I will keep all your ideas in mind

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Here's a pic from last week. Theres 11 miles of flat salt under all that water. Next bike will be lower and longer

IMG_20140812_152739.jpg

Edited by sofadriver

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I remember Dirt bike mag having Rod Bush in the early 80's running a ktm open bike to a max of 125mph with gearing and slight aero work.

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I would contact lectron fuel systems and have them build a custom carb for your specs, fuel, use, and tune.

Race gas, radical top end porting, top end pipe, long silencer experiment with optimal length tuning, lighten engine internals, isf polished transmission, i believe lighter clutch baskets and plates are available, use ti and aluminum fastebers on the engine and bike.

Good luck post up results and updates sounds cool. Be as secretive as yoy want with the frame and body, but keep us clued in with the engine.

Contacting various high end "cart" engine builders would be a wise choice as racing go carts are tuned tor very fast very peaky engine delivery much more agressive delivery and output then is usable or typical in mx.

Edited by yz133rider

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sofadriver...I am just getting started on a similar project.  Plan to run a KX100 with the ECTA and maybe one day get to Bonneville.

What to do...

Well there are two things...A. More Horsepower and B. Reduce Drag.

A. Remember the engine is nothing more than a big air pump and you want to flow as much air as possible.  Porting is equivalent to the cam in a four stroke motor and you need someone who understands the effect of each and every change that can be made to the porting.  For instance raising the exhaust port will give you more high rpm horsepower but at the expense of low rpm horsepower.  The KIPS system may be able to help but my guess is you want to remove it entirely and smooth out every little bump, nook, and cranny to maximize flow out of the exhaust.  Exhaust (pipe) design) is another critical factor for a two stroke...you are basically trying to get a low pressure pulse at the piston when the exhaust port opens so you can suck the air out of the cylinder better.  Only about a gazillion other factors that affect optimizing the air pump (engine) and each has a positive and a negative to consider.

Gearing...AFTER you get good rear wheel dyno data make sure you gear it so you are achieving the max horsepower and the max speed at the same time.  And of course there will be a lot of trial and error because the drag changes when the speed changes.

B. Drag...it is the thing that is keeping you from going faster so you want to minimize it every way possible, both frictional drag in the motor and aerodynamic drag outside the motor.  If possible get a good modeler to set up your vehicles shape and play with changes to see how you can reduce the "Form" drag.  Frictional drag of the body is something most overlook...it usually isn't as big of a factor as form drag but you are looking for every little bit you can get.  I don't have the answer but since you are traveling below the speed of sound, breaking up the boundary layer may help i.e. a rough surface like a golf ball.  Frontal area...duhhh, reduce it every way possible.

I could go on and on...

Question for you...where did you get your rear sprockets and are you running the stock Kawasaki KX100 rear hub?  I am having trouble finding anything smaller than a 47 tooth rear sprocket.

Thanks

Yes, I know this is an old thread...but it is exactly what I plan to do in the long run :).

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