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Originally Posted by graywolf624
Im still waiting on a correlation here.
You just admited that pushrods are generally smaller and lighter then regular engines.
You also admited that mpg is not correlated to liters of engine.
What do you have to fall back on now.. Still hp/liter has no meaning in the real world. It doesnt mean the engine will be lighter, it doesnt mean the engine will be more economical, it doesnt mean the engine revs higher, it doesnt mean the engine is smaller in size.
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Waiting for a correlation between what?
You say I admitted that pushrod engines are gnerally smaller and lighter than regular engines like i disagreed with you. I didnt disagree with you, i misunderstood you in the first place and then I agreed with you.....
I didnt admit mpg is not correlated to liters of engine - i havent compared them.... They are however correlated, negatively. GENERALLY as displacement increase, mpg decreases.
HP/litre is useful as other members have said.
It is related to the efficiency of the engine as i've said many times - as in how much power you get out of the engine compared to the air/fuel mixture you put in. It takes revs into account because the figure you use for HP is when the engine is at maximum revs.
The 3 basic principles of engines:
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Mechanical efficiency - Basically, the less friction, the more HP
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Volumetric Efficiency - The more air/fuel mixture you can get into the combustion chamber, the more HP you will create. The maximum is the size of the combustion chamber (for an NA engine), but in practice this is very hard to accomplish
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Thermal Efficiency - This is how efficiently the engine burns fuel. It is calculated as a percentage of how much horsepower is produced compared to how much stored energy was in the fuel that was combusted in the engine.
These are the 3 main, basic principles you have to tak into consideration when building an engine. HP/litre shows us as a general figure a combination of these 3, and therefore an idea of how efficient an engine is.
Its by no means the only thing that can and should be used but is a good figure.