Quote:
Originally Posted by woodydel
The engine is a pump. For every revolution the same amount of air is pumped. Some engines pump air better at differing RPM's. That doesn't matter. As the air is pumped through the engine, if you squirt less fuel per revolution you HAVE TO USE LESS FUEL. So you call it lean burn because there is an excess of air available for any particular volume of fuel squirted into the airstream in a given amount of time.
All the talk about whether you get more or less power means NOTHING. It doesn't matter if you're able to climb a hill or not. Working your throttle to hold back the amount of air the engine can pump DOES NOT change anything I stated in the previous paragraph.
Squirting less fuel in any given time period when the engine is running has to use less fuel. The consequences of the "lean burn" don't mean anything. A "lean burn" is just harder to maintain. It does not matter how you squirt the fuel into the engine. Carburetor, fuel injection, a BUCKET will not make any difference. Obviously a BUCKET will not be a "lean burn". All you're doing is measuring how much fuel goes through the engine with the air.
I think people are making this out to be complicated for no reason. Even Einstein knew enough to look at things simply.
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Compression ratios are calculated by considering the bore and stroke as well as the volume of the combustion chamber area that is still present at TDC.
That represents the theoretical maximum compression ratio. In reality any restriction present that reduces the amount of air that is actually in the cylinder at BDC reduces the usable (I call it effective) compression of the engine. In some cases cam timing can allow the atmospheric pressure to actually push more air in the cylinder than the measured theoretical compression.
When you have a manifold reading of 14 inches, you are only allowing the remaining inches of measured air into the cylinders, so to say that the same amount of air always passes through and engine is incorrect. You can confirm this by just considering the exhaust exiting the tailpipe. At idle it is a very small amount, Rev the engine up and the amount vastly increases.
Lean burn, when properly designed and utilized compensates for engine operation states where manifold vacuum is fairly high, probably above 40% of atmospheric pressure. Effective compression is much lower than the potential maximum.
Since higher effective compression creates more pressure during combustion, lean burn allows for the compression to be slightly higher, while preventing the power from being more than is necessary.
regards
Mech