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Posted by: will pattison
it's been tried, at least partly. i actually did my graduate work with a consultant who wanted to build a supercharger for small-bore 4-stroke motorcyle engines. my part of it was the prototyping and engineering design part, and he was the theory guy. after lots of number crunching, he settled on a roots type blower because he felt it had the best "return on investment". it actually takes a lot of power to run a blower, so you have kind of a catch-22. we actually built a roots blower prototype that would have fit into a 6" cube. very cute. well, until we tested it, that is. roots blowers make an obnoxious amount of noise while they're busy smashing air. we hooked the thing up to a 15hp cnc mill to turn it, and the sound was unbelievable. it made an uncorked yz450 sound like an electric toothbrush! then...it was time to graduate, so i went out and earned some dough so i could RIDE bikes instead of tinker with them. don't think he ever did any more with the idea, but i still have some extra casting patterns for the rotors....
wp.
Posted by: fishy7509
my friend was also interested in super charging a four stroke engine however he decide to super charge his yamaha golf cart. due to the issue of being cost effective and cheap he decide to use a pollution pump from a 350 chevy, pick up truck . he thought of this idea and then tried to reserch this idea and found one other person who has done this. if u would like to see the website search for dirt cheap super chargers. after several failed atempts due to over heating of the super charger and intercooler he has deicided to build a water jacket aroud the smog pump.he is using 2 transmisson coolers from cavilers and a 121 millimeter computer fan to cool the water and a water pump for a single sink in a motor home. he is waiting to get the water jacket welded so he can test the new theory if u have any ?'s comments or possible improvments please post and i will have him check this forum.
Posted by: berudd
fishy, your boy had waaaaaay to much time on his hands! 
Posted by: LJW
Will,
What configuration were the rotors?
Posted by: DirtRoller
I know this isn't a small bore. Did the blower work on this bike.http://www.freeridesouth.com/pics/pictures/1896.jpg
How tight you run the tolerances on a blower will have a lot to do with how much noise,heat and HP it will make.
Fishy, I have used smog pumps for crank case evacuators.
I have not tried using one for a supercharger.
Sounds like fun. With enough time and money anything is possible.
"suck squish bang blow".
Posted by: Hogwylde
I snuck into the Indy Motorcycle Dealer expo this past weekend and saw a turbocharged 4stroke quad setup from some company I can't remember the name of now. If you're thinking about it.....probably someone out there is already DOING it. It all depends on how fast you want to go and how much money you have.
(Anyone want any confidential dealer price lists?)
Posted by: cujet
Roots blowers are known for inefficiency, noise and large size. Those items alone make them less than desirable for dirt bike applications. Other more modern positive displacement designs are better and smaller. One of the most interesting ideas I have ever seen was posted on here on DRN a few years ago. The application is on Shindawa 4 stroke weed wacker engines. Shindawa uses the crankcase of the engine like a 2 stroke. So, every upstroke of the piston draws in fuel/oil and air. It is then compressed by the down stroke. This results in some boost being available to the engine, as the 4 stroke engine only draws air once every 2 revolutions. Very clever indeed! No additional blower necessary.
Maybe a CR450F would be a good candidate for experimentation.
Turbo's make a lot of sense. My very favorite, the Aerodyne has been reborn as the iBoost. It is a self lubricating variable vane (no wastegate!) turbo. They can be sized to nearly every engine size. They weigh about 8 pounds, but can be made much lighter if necessary.
Chris
Posted by: Rich Rohrich
There is certainly interest in this subject at least at the research level. Here's a couple of interesting papers on the subject.
SAE Paper # 1999-01-3318 Advanced super charge system for small engines
Author(s):
Shunzo Fujiwara- Yamaha Motor Co., Ltd. , Nobuo Norimatsu - Yamaha Motor Co., Ltd., Jun Taue - Yamaha Motor Co., Ltd.
Abstract:
The specific output of 4-cycle engines are generally smaller than that of 2-cycle engines. Increasing engine speed is one method to improve the specific output; however, it contains some disadvantages in application. Hence, improvement in torque with the 4-cycle engine is desirable. Although torque could be improved by supercharging, it seems difficult to apply existing systems for small displacement engines due to problems of their size and cost.
We have, therefore, newly developed a supercharging system named Advanced Crankcase Super Charge (hereinafter referred to as ACSC) using a crankcase as a supercharger. In this study, we made a 50 cc single-cylinder prototype engine with ACSC and carried out the engine unit tests and actual running tests on a scooter. From these tests, the torque that is twice as that of the naturally aspirated engine was obtained.
In addition, the driving performance equivalent to that of the vehicle with 2-cycle engine was achieved in the actual running test. It was also confirmed that the emission level was equivalent to that of a vehicle with a naturally aspirated engine. There was also an improvement in fuel consumption compared to the vehicle with 2-cycle engine.
SAE paper # 961030 Simulation techniques applied to the development of a 125cc 4 stroke scooter engine
Author(s):
Vittorio Urciuoli -Ricardo Consulting Engineers, Brian Mason -Ricardo Consulting Engineers, Maurizio Marcacc - Piaggio Veicoli Europei Spa
Abstract:
In the automotive industry, computer simulation techniques have been developed to improve the 4-stroke engine development process. The objectives are to reduce engine development time, optimize engine performance, improve refinement, and to achieve legislative noise and emissions requirements. The application of these methods to a 4 stroke scooter engine has been evaluated. This paper describes how computer simulation techniques have been used to assist with the development of a new 125cc 2 valve 4 stroke scooter engine built by Piaggio Veicoli Europei Spa, and to evaluate an advanced 4-stroke scooter engine concept.
A single dimensional fluid dynamic analysis code WAVE has been used to simulate engine performance and inlet-exhaust noise during prototype development. To support this analysis, pseudo-static valve train analysis using a multi-polynomial camshaft design approach has been used to optimize valve train performance. In addition, port development techniques have been applied to optimize the trade off between part load combustion stability and full load volumetric efficiency requirements. A potentially high specific output engine derivative based on a crankcase supercharged 4 stroke concept has also been evaluated by computer simulation.
Posted by: Danappger
Using the crankcase to supercharge a 4-stroke engine would seem to have little advantage over a 2-stroke. You'd still have to have oil in the fuel, with all the resultant unburned hydrocarbons in the exhaust, and the problem of frying the engine if you run it too lean.
I'd think a better approach would be to use a blower to feed a 2-stroke engine. This way, you could have a conventional oil filled crankcase so you wouldn't need oil in the fuel, and you could run it lean without the danger of damage... though whether you could build it light enough to compete with a 4-stroke I don't know.
-Dana
How is it that 2 teenagers in the back of an original Volkswagen Beetle, in a crowded drive-in theater, can reproduce, yet it takes 2 spotted owls 10,000 acres?
Posted by: #1YZ125RACER
what if you used one of those electric blowers..have seen lots of differant types,eram and such,pretty much the same as marine fume blowers...just a thought
Posted by: KiwiBird
Before Maico went belly up they were working on a crankcase supercharged 4 stroke.
25+ years ago I read an article in a dirtbike mag (Modern Cycle maybe?) that someone put a supercharger on a CR125 which caused a number transmission failures.
Posted by: xsnrg
How about replacing the seat cushion with a bladder and a hose, so that you could sit and squeeze compressed air out? This might add HP and reduce monkeybutt at the same time. If anyone patents this idea, I ask for no compensation, but please name it the Whoopee Blower.
Oh, and if it made a farting noise at the time of decompression, that would entertain the trackside fans immensely as well.
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