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MP3 Vs. '94 civic EX

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Old Nov 21, 2002 | 12:14 AM
  #16  
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Re: VTEC

Originally posted by nate0123
One thing I've always wondered about variable valve timing is that, if they can enhance performance in a narrow band - doesn't that mean the car could perform better if the altered timing were applied to a wider band?

Another way of thinking about this is that the car is being choked up to 5500 rpm... For fuel economy?
well actually no. MOST of the variable valve timing technology is designed to alter the intake and exhaust valve opening/closing rates to improve engine breathing AT HIGH RPMs. Running in this valve timing profile in low RPM will actually DECREASE torque output, as the air is not flowing in fast enough to fill the intake and exhaust valve's needs, and the engine bogs down.

that's the gist of variable valve timing and what its main objective is. The details I cannot explain as I did not take the time to study into it. But to answer your question, changing the timing to open up the alternative valve timing profile at a lower rpm MAY increase top-end power output, but it will almost certainly KILL any tiny bits of low RPM torques these high revving 4 cylinders have....

Edwin or Jesse or anyone more informed can go ahead and correct any misinformation that I may have pulled out of my a$$, but I think I've cut that to a minimum
Old Nov 21, 2002 | 02:07 AM
  #17  
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There's specific timings that make the engine run optimally at different RPMs. Ferarri implements cam lobes which are elongated from side to side to allow for highly optimized cam timing at every engine speed. As RPMs increase, the camshaft slides sideways a bit and that way the timing changes and the engine always performs very well.

VTEC is basically the same thing, but the timing is optimized for only one narrow band of engine speed (on my friend's Si it kicks in at around 5500 rpm and goes all the way up to 8200 rpm).
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