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Re: Benefits of higher compression?.
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Posted by Ron on June 26, 2004 at 09:35:52 from (69.179.4.15):
In Reply to: Benefits of higher compression?. posted by Jonathan on June 26, 2004 at 08:32:41:
Thanks for asking such a thoughtful question. That's what makes this group such fun. Whenever you compress a gas (air/fuel mixture here) you heat it. The greater the compression, the more heat; the more heat, the more power. Remember, it's the expansion of the air/fuel charge as it burns that drives the piston. So yes, in that sense, it is more efficient. This is exactly how diesels work and why they are more efficient than gas engines. As you have observed, the heat from higher compression ratios must be managed. Should the cylinder become too hot, spontaneous combustion (knock) occurs and power is decreased... if continued too long, you start breaking parts. Octane enhancement is only one way of managing spontaneous combustion. See http://www.kb-silvolite.com/article.php?action=read&A_id=36
for more information. Your point about horsepower is true but far more important is the enormous low rpm torque improvement in higher compression engines. I was a kid in the '60's when there were lots of cars sporting 400-450 ci. engines running as high as 11:1-11.5:1 compression ratios. Many of these engine made over 500 lb./ft. of torque and the acceleration was mind-blowing. For tractors, torque is all that matters. And the more torque you can build at low engine speed the better. Higher compression ratios are the best way to make more low speed torque. An old rule of thumb is that for each full point you gain 10% in torque. For example, going from 8:1 to 10:1 should net you about a 20% torque gain.
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