Cheap expansion chamber

Also, most people say port and polish ..while that works great with unmixed fuel. Studies have shown leaving a rough surface helps to atomize oil and gas for better ignition.
This is true thats why you see dimpled intake manifolds for performance cars. The dimples are like a golfball the trapped air in the dimples create a forcefield type effect which allows smoother air to travel on top of that forcefield. However on a small application such as the china girl motor it will have little to no effect. Plus the dimples would have to be perfectlly spaced for smooth flow
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My bike does 50mph with my 220lbs butt on a steel frame. 40mm stroke, ported allaround, Piston crown ramps, needle bearing spacers, balanced crank, scooter cdi, advanced timing, 36t sprocket, expansion chamber, short intake, velocity stack, 6cc head with .02 squish gap
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You guys lose me sometimes with all the technical details. I do understand the basic concepts of what you are saying though. The golf ball thing is pretty cool how it works. You ever see the mythbusters episode where they dimpled a whole car to see if it was more aerodynamic?
 
You guys lose me sometimes with all the technical details. I do understand the basic concepts of what you are saying though. The golf ball thing is pretty cool how it works. You ever see the mythbusters episode where they dimpled a whole car to see if it was more aerodynamic?
Lol no but that show is entertaining. Two very smart dudes. They make Bill Nye look like an english teacher
 
The rough intake surface isn't so much about atomizing the fuel as it is about 2 other aspects of how the air travels.

1. The boundry layer effect. This effect is caused by the imperfections in the surface, and as the air passes over the peaks and valleys it creates microscopic eddies of air swirls. These swirls both prevent fuel from sticking to the walls as easily when the engine is cold but also create a cushion of turbulent airflow for the next "layer" of air traveling over it. That leads to the second effect.

2. Increased total volume through velocity. Those little eddies of swirling air act, in essence, like bearings under a sheet of paper. This effect increases the velocity of the air closer to the surface by reducing the drag on the molecules over a larger area than a smooth wall would create. In a standard column of air, the highest velocity is found in the center, and the further out from center you go, the slower the velocity becomes. By having a boundry layer at the surface on the outer edges, this allows the velocity of the air molecules to stay higher as you move away from the center, and thus increases total volume for a given amount of time.

The boundry layer and high velocity just have the added bonus of assisting in a higher total swirl, contributing to better atomization

Polishing of the combustion chamber, piston top, and exhaust is done to have 2 primary effects. One is to try and reduce carbon deposits. More on that later. Two is to create a higher heat emissivity effect.

Polished metal surfaces both reflect and transfer heat more efficiently than rough surfaces. This means that the very top layer where the metal is polished with gather and "reflect" it away rapidly. The effect is intended to be an increase in thermal efficiency.

That also means that it should, in theory, prevent carbon from sticking as easily due to the brief moment of high surface temp. Polished finely enough and it will also reduce the mechanical means for carbon to "latch on" to the surfaces during operation.

I take the time to polish to as close to a mirror as I can because I have seen for myself the limited ability for carbon to build up and stay. Any other potential benefits I just consider perks, if they do anything for me at all.
 
I have a mild amount of experience in engine theory and tuning... if it shows. I used to do the calculations for intake resonance to setup velocity stacks on race bikes as well as some porting and other machine work.

If you ever wondered why Lamborghini and Ferrari engine intakes sound like musical instruments at high RPM - intake harmonics tuning at work.

The real brain bender is when you get into the reality of those harmonic waves, and how they are applied to engine tuning, some of the old "wives tales" somewhat go out the window. The "longer intakes make more power at lower RPM" for example, is both true and untrue.

A longer intake at the same harmonic wave position does, but if you tune for a higher harmonic resonance at a higher resonance strength (lower position) then it will still benefit higher RPM power, and the effect is greater.

This is due to how harmonic waves behave. The time it takes for the wave to be sent from the node, hit the anode, and return happens over a given distance. If it occours in one pulse, it is known as a first harmonic. The issue is, first harmonics require a very long distance to travel, usually several meters, which is a bit unreasonable to fit in an engine bay, so engineers have to cut down the distance.

If you halve the distance it needs to travel, the wave will reflect off the node position, go back to the anode, and return. This is the second harmonic wave. This effect keeps happening until the node is opened. In most automotive application the intake tract is tuned to the 4th or 5th Harmonic wave.

If your brain hurts yet, don't feel bad lol
 
So the wave usually travels back and forth 4 or 5 times before it is taken in by the engine?
 
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