spacer wrote:To answer some of them: static compression in current V8's won't be much higher than 1:12.5-13. Due to high valve-lift and short stroke there simply isn't much room left in the combustion chamber to increase the static compression ratio much higher without losing on VE (according to the RET issue about the toyota V8).
AS far as the 100% VE: due to intake and exhaust length tuning, VE's above 100% are actually quite common in high-end N/A engines.
With a spark-ignited engine, having a high dynamic CR at start-up is not so critical. The engines are fuel injected, have high voltage CD ignitions, and can be preheated before start-up. The start-up cranking speed is probably only about 400 or 500 rpm. Even though the engines use external starters, going faster would require excessively large starter motors.
The engines idle at high speeds mostly due to low polar intertia in the engine's rotating components. They accelerate fast, but they also lose speed just as fast.
As others noted, VE can far exceed 100% at some engine speeds, due to charge inertia and acoustic effects.
Shafto wrote:you bring up a point i want to research, I was thinking about direct injected gas engines a while back and started thinking about there ignition system. Then I thought, well if they are truly DIRECT injection then they would not need a spark plug... That is what i have to research. I am sure they do still use spark plugs but I would think that if you can inject directly then why not up the compression ratio and when the fuel gets injected it will spontaneously ignite as diesel but I am guessing that it is too erratic and un controlled in a gasoline engine. Just as detonation and pre ignition.
And how am I going to do an audio analysis of one cranking?
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