My stupid experiment & the results (the supercharger effect)

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moronic_kaos

New Member
Apr 6, 2010
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Connecticut
Haven't really invested a whole lot of time and effort on this one, but i did do a little experimentation with a ghetto-supercharger system, and the results were quite interesting.

Now I'm not 100% fluent with how and why a supercharger works, but the basic concept I have of it is that it's a blower that crams more air through the carb, which also at the same time makes it draw more gas, cramming in more air & gas per stroke, which would be sort of like being able to open the throttle more than usual & the more powerful explosion = more pressure on the piston & eventually the wheel.

So I had a pretty powerful blower laying around, one of those colman airbed inflators. The pressure isn't really all that great, but it does move a whole lot of air very quickly. So I said screw it, removed my air filter and pointed the thing through the carburetor hole.

After a couple tries, I was able to get it a certain distance from the carburetor and it rev'd up without stalling. Went through the RPM range with the throttle, and at no point did it bog down or anything unless I accidentally moved the pump (I was holding it with the other hand). It rev'd up a lot higher than normal at all ranges without bogging down or delaying the throttle.

So I'm thinking about finishing this when I have the time and money. The carburetor cover would get a hole cut in the front of it with an intake piece coming out and rigged up to a hose running to the pump, and at some point there would be a 3-way pipe fitting normally used for joining two pipes into one. At the end of one of those spots would be a valve opening up to the outside, decreasing both the amount of air and pressure going into the carburetor and since it's a valve it would be able to be tuned properly. The only complication would be the fact that this air pump runs somewhere near 150 watts, in which case I'd need to find a suitable battery and a power inverter & mount it on a rear rack.

Since it's run off a battery, the system would be able to be switched on and off (big red push button) from the bars to conserve power and only be run when necessary. This would also make tuning it easier if the power-band ends up being limited, tuning it to either perform during hill-climbing RPM's or MAYBE to get a little speed out of it (would have to gear the bike differently so as not to over-rev the thing), and shutting off the system during all other stages of driving.

EDIT: Was thinking one of those small batteries meant for electric scooters, as they can power a 250-watt motor for an hour straight & handle draining and recharging pretty well, unlike an automotive battery. Plus they're considerably small, light, and inexpensive.

[QUOTE="K" from Men In Black]
Whatever you do, never, EVER, touch the red button...
[/QUOTE]
 

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thuginfc

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Nov 28, 2009
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F.W.B. Florida
basically all your doing is leaning out the air fuel mixture by shoving more air in than is needed. that being the reason for the higher revs and alot more stress and heat on youre engine
 

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,837
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up north now
Yep, with these two strokes, if you are getting a higher rpm by doing what you are doing, you are just "adjusting" the mixture to a more correct mixture, ie leaning it out some.
 

moronic_kaos

New Member
Apr 6, 2010
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Connecticut
So what if the fuel was increased to match, i.e. a larger jet size, perhaps a second carburetor tuned for use solely for the supercharger? There's gotta be some way to cram more mixture into these engines besides porting and using the motor's natural vacuum.

I'm well aware of the fact that the motor wont be able to take the stress for very long, but I don't think it'l have a problem with short 10 to 30 second bursts as long as it doesn't get over-rev'd.
 
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Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,837
252
63
up north now
So what if the fuel was increased to match, i.e. a larger jet size, perhaps a second carburetor tuned for use solely for the supercharger? There's gotta be some way to cram more mixture into these engines besides porting and using the motor's natural vacuum.

I'm well aware of the fact that the motor wont be able to take the stress for very long, but I don't think it'l have a problem with short 10 to 30 second bursts as long as it doesn't get over-rev'd.
Install a reed set up....it will gain you something for your time and effort.
 

GearNut

Active Member
Aug 19, 2009
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San Diego, Kaliforgnia
If you can do it without blowing up the blower, put the blower in between the carb and engine so that way all the air is sucked through the carb. Carbs do not really like to be pressurized. You will end up with a draw through system, like an older technology turbo system (newer ones uses fuel injection). Just be carefull as there will be fuel and air passing through the blower, and if there is the slightest chance of ignition occurring inside the blower then.... BOOM!!! Parts flying everywhere at high speeds.
DO IT AT YOUR OWN RISK!
 

Ted

New Member
Apr 20, 2010
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Leavenworth Wa.
Several things to consider..as with 4strokes the overlap between intake and exh timing needs to be optimised..a 4 stroke has an induction stroke to allow time for the cylinder charge to be pressurise before the inlet valve closes for compression..a 2stroke does not have this luxury so the exh port/transfer port overlap has to be drastically altered and you still won't have positive pressure as the exh port is closed by the piston..2stroke diesels either have an exh valve in the head (with intake ports in the bottom of the cylinder skirt)..or they run slidding sleeve valves that are activated and timed from a camshaft/cranked arrangement which allows the intake ports to close after the exh ports..this is not possible with piston actuated cylinder ports.

If you supercharged a conventional 2stroke design you can get positive pressure in the cranckcase fine..but all the pressure does is blow more charge out through the exh port through the transfer phase..no advantage gained
 

GearNut

Active Member
Aug 19, 2009
5,104
11
38
San Diego, Kaliforgnia
That makes alot of sense, Ted. I was wondering about that, considering that the exhaust port opens before the transfer ports open and closes after they do too. It seems to me that any greater intake charge potential would be lost before the exhaust port closes.
 

Cabinfever1977

New Member
Mar 23, 2009
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Upstate,NY
Thats what i said, these 2-strokes with no valves suck all the air/fuel that they need, blow more air/fuel in faster and it just gets blown out the exhaust.
 

Buzzard

Member
Jul 9, 2008
264
5
18
Lincoln, NE
Heres' something that might be a little interesting. The older Detroit Diesel engines were 2cycle 4 valves per cylinder intake ports in the liners with a roots supercharger maximum goverened rpm was 2100, the later models also used turbochargers. If you ever heard one run at full governor speed you swear it was turning up 7000rpm. That's why they call them Rocky Mountain Humming Birds. If you ever drove over the road rig with one of these engines you had to drive it like you slammed your thumb in the door... wide open all the way. Double clutch a 13 speed transmission and work your butt off just to keep your road speed up. The 71 series 318 was rated at 318hp. The later ones with the turbo chargers were rated at 390hp. I thought this might be of a little interest.
I had a 1964 VW Beetle that I installed a plaxton centrifical belt drive supercharger on. Sealed and rejetted the carb. had a variable waste gate set at 6lbs of boost. It would not come on until I got upto about 1800rpm and it kicked up the little 35hp engine to about 45hp. It was really fun to drive till I started tinkering with the waste gate and burned holes in top of all my pistons and had to replace the motor.