Misconceptions about displacement.

[Marc91GSX]

Disclaimer:

1) This thread is not a what is better for my car thread. It is simply to explain what displacement is and why more displacement means more power PERIOD.

2) Not all info in this thread will be 100% accurate, I am not a mechanical engineer or automotvie genius, and I only have 15 years of experience with internal combustion engines so I may be misinformed on some the info that I post.

3) This is just a rant that I hope will help people.


Ok heres the deal, I am sick and tired of explaining to people around me what displacement is and how it effects performance. First off displacment refers to the amount of air an engine can take in naturally. Basicly a 2.0 liter engine will hold 2.0 liters of liquid or air. This amount comes from the size of the cylinder when the piston is at bottom dead center added across all four cylinders.

Now that we know what displacement is lets find out how it affects performance. I will assume that every one knows how a four stroke engine operates so I will not bother repeating that information. An engines power comes from it's abillity to take in, compress, ignite, and expel air and fuel.

Ok no that we know what displacement is and how your engine makes pwer let's discuss how displacement affects power. First off i will say this, there is no replacement for displacement. Despite everyones opinions on this board and in other areas, the old hot rodders jargin is true. I know, I know; that everyone will say that power adders equal or better large displacements advantage. That may be true if the larger engine is naturally aspirated, but what if the larger engine is boosted as well. Well, then it's larger displacement will again make more power than the smaller engine. Why is this you ask? Well let me tell you.

cont.

 

[Marc91GSX]

Ok why does a larger displacement engine make more power, well the answer is simple, it can move more air. Now let me explain to you why a boosted engine is considered the only competetion for naturally aspirated large displacement engines.

A naturally aspirated engine takes in air at an average pressure of 14.7 psi at sea level. That number gets smaller the higher the elevation becomes. The reason superchargers and turbos increase your engines performance is because they compress that air and shove it into your engine. What does this do? Well if you understood what I told you about displacement then you already know the answer. It effective increases the displacement of your engine. Basicly this means that all a power adder does is make your engine perform like a larger naturally aspirated engine.

I am through with my rant, please post your replies or disagreements with my info as I am always up to learning more. Also to all wisemen and mods if I have posted something false or against the rules I apologize. It is not my intent to mislead people in anyway and to the best of my knowledge all of this info is accurate.

Thank You

 

[leakyfaucet]

Basicly a 2.0 liter engine will hold 2.0 liters of liquid or air. This amount comes from the size of the cylinder when the piston is at bottom dead center added across all four cylinders.

I would like to chime and correct this. Actually, if you were to open up a cylinder whose piston is at bottom dead center, and fill it up all the way, it would hold more than 1/4 of 2.0 liters. The 2 liters is the amount of air the pistons displace in their travel, there is still more room above the piston. If there weren't, then the compression would be outrageous.

 

[Marc91GSX]

I would like to chime and correct this. Actually, if you were to open up a cylinder whose piston is at bottom dead center, and fill it up all the way, it would hold more than 1/4 of 2.0 liters. The 2 liters is the amount of air the pistons displace in their travel, there is still more room above the piston. If there weren't, then the compression would be outrageous.

Thanks for the correction, I guess I worded it wrong.

 

[Nt-Eclipse-Dail]

Marc91GSX said, "I know, I know; that everyone will say that power adders equal or better large displacements advantage. That may be true if the larger engine is naturally aspirated, but what if the larger engine is boosted as well. Well, then it's larger displacement will again make more power than the smaller engine. Why is this you ask?"

Excellent points Marc91GSX!

When riding around in my Z, I fear no turbo... Why? Because I have 5.7l of displacement and one of these:

 

[luvmygst]

To put it simple a motor is basically an air pump. Meaning the more air you get in and out then the more power you get. More displacement more air. Thats about as simple as it gets.