on a thread made by that idiot of godspeed or dumb mutha..... well now to the topic and cyttt responded that it was a modified air pump. the way if feel about an engine is this by volume. Air is pressurized; point one when and a law of nature is that something that has more energy will move to an area of less energy. When the combustion in an engine is complete and the intake stroke begins there is an area of no oxygen or a void. Now people call it a vacuum well that would relate to outer space where there is an area of no air (maybe a few H particles and photons) if space was a vacuum it would suck all the Oxygen in the earth and we'd all die. Space like an empty combustion chamber would be a  void.  Air enters through the intake valve and fills the area as the piston moves down it creates more area but it is more than that I would call it "volume" as it goes down more void and more area of less pressure so the pressurized air comes in to fill it. (I'm trying to make it short so I don't bore people so work with me here) Skipping to the main point after combustion. There is now an area of  higher pressure of NOx CO2 and Hydrocarbons plus O2 I think.... As the exaust valve opens the high pressure gasses escape to the less pressurized ambient or semi in this case... Air actually ecapes on its own and the exhaust stroke is only to help (in my opinion) "push" the exhaust gasses out.

I don't know if my opinion has much of a base that that's how I see things. I'm not an engineer but I can somewhat understand a couple of things.... I guess I don't know New Mexico has some of the crappiest schools (cool teachers), but other wise crappy to hell schools....  

to make my point or idle south-western ramblings some sense... If you're in space your body would explode not because it's being sucked dry its because of your own liquids want to escape to the great beyond... but on the other hand if haven't fully counted gravity.... or did I?....ah screw it now I made myself more confused well I just wrote this to see if I made sense and to see another point of view....  

You have the correct ideas and what you say for the most part is correct and on par.  But what needs to be understood is that pressure and matter or lack there of (void as you say) are basically the same thing.  This time I’ll use word so I don’t lose my work;  this is what I meant to say on the previous post.  

A pump is a modified air pump.  Delete strokes 2 and 3, turn the crank and the engine will be a pump.  The workings of the otto or traditional 4 stroke is as follows:

Stroke 1:  This stroke is where the piston moves downward, and in doing so more volume is created.  From chemistry we know that

PV=nRT  (1)

Where P= pressure, V=volume, n=moles (amount) of material, R=gas constant, T=Temperature.  This equation is for the ideal case, but it is a good representation.  So when the piston moves down there is a larger amount of volume.  Volume is inversely proportional to pressure.  So as volume increases, pressure decreases.  The pressure decrease creates a pressure difference between the air surrounding your car and inside the cylinder.   So there is a partial vacuum not a total, but a vacuum in that the pressure inside your cylinder is less then that of the atmospheric pressure of 14.7psi.  This decrease in pressure which can also be related to amount of material in the cylinder by equation 1.  So as air is drawn in by the difference in pressure more material flows in as well.  

Stroke 2.  The intake valve(s) close and the fuel/air mixture is compressed because the volume is decreasing.  As this mixture compresses temperature increases as well (hopefully not enough to pre-ignite).  So ignition occurs, in case of non diesels via a spark plug.  

Stroke 3.  Combustion starts and temperature rises.  This temperature rise creates more pressure pushing the piston down.  But another increase of pressure is due to the fact that there is more moles of material in the cylinder.  This means that the combustion products are less dense by law and more pressure is exerted.  Sorry the definition of a “mole” might be a little unclear, but I’m trying not to go into too much detail  

Stroke 4.  Once stroke 3 has reached the bottom, stroke 4 starts.  While the contents of the cylinder are higher pressure then the outside pressure ( the use of catalytic converters and mufflers exaggerate the need for a 4 stroke engine)  stroke 4 is still needed to push the exaust gases out.  

You just have to remember that pressure is created by materials.  The more material in a given space the higher the pressure.  That’s why space is a much lower pressure.  The only thing keeping the gas on earth here is the earths gravitational force.  

Awesome thread guys...lol.

Space is a vaccuum because, as it was stated, there is a lack of matter, however, its not really a total void. It wouldn't suck your guts out either, its not that strong. If it was, we'd have drasticly different space suits that would look more like the ones deep sea divers use. Now, if you were to cut your thumb and stick it out into space, my guess is you'd bleed out pretty quickly.  

hey it doesnt hurt to ask