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Old 09-02-2012, 01:43 PM   #7 (permalink)
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The vibration you feel is the engine going below its best minimum RPM for the load applied whne you are in 5th. My Civic VX would do 1000 RPM in 5th just fine but it was designed to run at that low RPM. If you are recording better FE in 4th then 1200 is probably your best minimum RPM. That may change depending on the vehicle load, like when you are climbing or descending a grade (small hill). At too low RPM an engine will loose the harmonics of the induction pulse, which hurts the AF mixture and efficiency.


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