Scudd

Topic pretty much says it all. I could not find much explaining it using "search". Thanks :confused:

mrvette

Well, to a certain extent it's what makes the engine run, in the first place....taking a mist of gasoline and fumes in open air, light it off and you get a burst of flames, and a puff, but since it's not directed....all that heat is wasted....
so to turn a crank with a piston, the piston moves up and down in the cylinder a goodly bit...3-4 inches....and as such is sealed to capture the burning gas and air into an enclosed space.....the comperession takes place from pulling the air/gas mix into the cylinder, the intake valve (trap door) closing, the piston traveling to the top of the cylinder, near the valves, and the the plug igniting the mix....thereby blowing the piston down to the bottom of the cylinder, then the spent gasses are exhausted our another valve (trap door) and the 'cycle' repeats itself.....ONE power stroke for every two turns of the crank. or 4 trips up and down the cylinger length...the compression takes place when the gasses are drawn in on the down stroke, and on the upstroke with all the valves closed, that air/gas mix is compressed by a calculation of the 'displacement' of the piston, vs the size of the hollowed out combustion chamber in the valve holder...(cylinder head)..... so that is expressed as a ratio....say 10:1 meaning say for example the total volume of the cylinder with piston at bottom is say 100 CC's.... and the volume of the head is say 10 cc.s.....that is a ten to one compression ratio...pretty close for understanding sake anyway....not trying to snowball you here, just make it clear before my fingers tire out.....

GENE

OHSIXX

Gene: I think you cleared that up pretty well. That is quite an explanation; now go take an asprin. :)

Pete79L82

Gene did an exellent job of explaining what compression is. The reason it is so important is because when everything is optimized for it, the more compression you have the more torque/horsepower/throttle response you will have. But there are limiting factors as to how much compression you can have. Things like cylinder head design, intake tract efficiency, piston design, camshaft design, cooling system design, ignition system design, fuel quality all play in harmony as to how much compression a particular motor can have. Anytime you exceed the limitations of those designs you will get cylinder detination and severe damage can accoure inside the engine. On a chevrolet small block and big block the average range of compression is between 9.0-1 and 11.0-1 for a street driven motor. Some guys can run a little more than that with a good head design and cam package and keeping the motor in good tune.


[Modified by Pete79L82, 8:46 AM 8/17/2003]

Larry B.

Compression is what makes power. Compression also creates heat. When the compressed gasses get to a certain temperature they ignite: explosively. The higher the compression the quicker the gasses ignite and vice versa. Octane is a method of slowing the process down. High compression and low octane make for detonation, spark knock or pinging. Reducing the compression to a point that you can use pump gas is the trick. If you have access to 100-110 octane you can make a lot of power with high compression without detonation problems... Otherwise retarding the timing will help eliminate the problem but at the expense of power. Lowering the compression is a better method than retarding the timing. I know I kinda got off of the main topic but it is related. Compression ratio is the amount of volume of the cylinder(with heads) at bottom dead center divided by the volume of the same cylinder when the piston is at top dead center.. So 100 cc's at the bottom and 10 cc's at the top would be 10:1. In other words the piston takes the air/fuel mixture and compresses it into an area 1/10th the volume.

76Frankenstein

Hours of fun at this site :thumbs:

http://auto.howstuffworks.com/engine.htm

USA SHARK

I'll take one of those aspirins too.... :crazy:

Scudd

Thanks Guys :chevy

mrvette

Pete, it's only important untill the engine stops running.....


:eek: :eek: :eek: :eek:

GENE :chevy :cry :cry :lolg: :reddevil