supercharger

Jacka$$withawrench

Jacka$$withawrench

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bob58o said:
Engine capacity 212cc
Air pumped 180cc
VE = 0.85

Engine capacity 212cc
Air pumped 300cc (forced induction)
150cc per revolution
VE = 1.41
Boost = 6 psi

I’m not sure I agree that volume of air doesn’t increase as well as air density. VE isnt even constant at different RPMs because of intake / exhaust tuning and scavenging.

Unless the VE was originally 1.00 when NA. I have to think about this. Air would flow faster with a greater pressure difference between runner and chamber and more volume could be moved in a certain amount of time. But the chamber being filled with dense air might offset the boost in the runner? I dunno. My fluid mechanical ignorance is showing.
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The engine would still take in the same volume of air, just a higher density of air, no? I looked into it online and that's what an old guy (Banks Power on facebook) is saying, that a supercharger increases density not volume and therefore doesn't increase Volumetric Efficiency.
 
bob58o

bob58o

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It’s a complex system. Piston moves down- creates low pressure in chamber. Piston moves up- increases pressure in chamber. Intake and exhaust valves open and close and have overlapping open periods. Air flows based on pressure difference. Intake and exhaust pressure waves pulling out spent change and pulling in fresh intake charge. People like to make simple models explaining what’s going on, but the reality is much more complicated.

Measuring the mass of the air and its density will give its volume.

We need Alex here to explain maths and to remind us jokes about German sausages are the wurst.
 
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bob58o

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The word I find most interesting in the following is “overfilling” of the cylinder


Forced induction has the ability to raise the VE of an engine to 100 percent and way beyond. It is a function of the airflow in cubic feet per minute (cfm) of the compressor and the boost pressure created. Boost is the positive pressure above atmospheric that is generated in the intake manifold.

…

Most of the power gain from forced induction is realized from the improved VE; the denser charge (the fuel and air molecules are closer together) put there is a side benefit—that is the pressure rise in the bore. In a normally aspirated engine when the piston is at bottom dead center, there is atmospheric pressure in the cylinder. Then as the piston sweeps toward top dead center, the area is made smaller and the pressure in the bore rises. This is a result of the compression ratio of the engine (the mathematical change in volume), the atmospheric pressure, and the volume taken by the charge.

When forced induction is applied, the beginning pressure in the cylinder is greater than atmospheric, and is a function of the boost level. Let's apply some numbers to make this clear. We'll assume that the atmospheric pressure is 15 psi and the boost pressure is 5 psi. Then the cylinder will be pressurized to 15 plus 5 or 20 psi before the piston starts to move upward. This higher pressure will then translate to a greater cylinder pressure when the flame expands across the bore and pushes against the piston.


There is no denying that the pressure rise from the forced induction is minimal compared to the gains from overfilling of the cylinder (VE) and the denser charge, but it does make a difference. For this reason, along with the improved VE, a forced-induction engine (especially one with a turbo) feels more powerful even when the boost gauge is reading zero. This is often not the case with a supercharger since it takes power to turn the compressor, and that is coming from the crankshaft.
 
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Thepartsguy

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The engine runs just fine it’s very smooth the slide does hang up I think due to the pressure so I’ll need another cap spring.
 
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www.youtube.com

Smog pump supercharged Briggs 4hp

www.youtube.com www.youtube.com

Ok so I have used three different gauges and all read the same.

12psi-14psi flutter at cruising and the gauge pegs at 15psi when wide open throttle flying down the street.

Could this setup really be making 15+ psi?? Included short YouTube video of the gauge readings at cruising.
43F538EE-69EC-413D-AE46-0E7F6EEF5D02.jpegEEDF3FC8-7CDF-49DD-9072-425521730700.jpeg47816058-8F86-44B9-B89C-4995BB997182.jpeg
 
Thepartsguy

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Denny said:
Does the engine feel stronger? The kart pull harder? Can you make the camera shake more?
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It’s the best I can get with an iPhone 4 that has half a usable touch screen. The engine at WOT feels oddly reminiscent of the 8hp engines I run. But with 15+ psi I’m not surprised. Can you see the video well enough or is it all screwed up? It seems to play enough to tell the boost readings on my end.
 
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Usually I never get motion sickness. After one time seeing that I almost threw up!
I once went on a dinner cruise on Lake Michigan in 12’ seas. My wife, my buddy and his wife and me were the only 4 people besides the crew not throwing up. I don’t get motion sick. That made me sick.
 
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Denny said:
Usually I never get motion sickness. After one time seeing that I almost threw up!
I once went on a dinner cruise on Lake Michigan in 12’ seas. My wife, my buddy and his wife and me were the only 4 people besides the crew not throwing up. I don’t get motion sick. That made me sick.
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Ehh I checked it on another computer and the video is fine to see the numbers. So it’s good I honestly don’t know how to tell if the gauge is right.. 15+ psi seems excessive.

I did do a lot to seal up the pump and make sure everything was clean. I’m running a light oil mix in the gas so I’m wondering if the oil mix going through the pump is helping seal the pump like oil seals piston rings. It is a tight fit from the vain to the scrubber.
 
Thepartsguy

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Denny said:
I can see it making that much boost quite easily on that tiny engine. Post some vids or pictures of take offs and high speed runs. None of that on/off throttle stuff.
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It Is pouring rain but Monday is supposed to be 80 degrees and sunny.

I’ll try to make a mount so the videos are not so shaky. On takeoff the gauge swings wildly from 4-8psi at cruising it swings from 12-14psi and wide open throttle flying down the road it just pegs the gauge at 15psi then when I let off the gauge slams back down to zero.

I will post more video i didn’t think the pump would even push 2psi
 
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A Manco Dingo said:
Yo that looks amazing and 15 pounds of boost thats insane btw are you going to do e85? Or nitromethane?
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I have no idea If the boost number is even right. I tested it with two gauges and they both read the same.

Someone said at 15+ psi there should be some oil spitting out of the breather but there is none.

15psi at the intake still seems to me like a false reading.

I have no billet rod or flywheel either I’m happy it runs with the pump at all I’m just gonna leave it alone.
 
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