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Old 04-21-2012, 12:17 PM   #59 (permalink)
The Mad Technician
Join Date: Apr 2012
Location: Devon, England, UK
Posts: 31

Rover - '98 Rover 218 iS
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I'd like to comment on the knock sensor statement. It may well be true on the lean burn honda engine that ignition timing will not be advanced, but that is not true on all engines. The Suburu Impreza for one will certainly adjust timing for higher octane fuels, and so will many others due to the knock sensor.

My particular model car does not have a knock sensor, but I've read carefully through the full documentation for the ECU system including how models with a knock sensor behave. They work by slowly advancing the timing (in this vehicle's case) 0.3 degrees at a time, then once engine knock is detected they immediately back off the timing by 0.3 degrees at a time until knock ceases. Then the cycle starts again.

In this way the ECU keeps the most advanced timing possible, giving the best performance results. My car does not do this therefore higher octane fuel will do nothing at all without a remap, but some cars definately can take advantage of it.

If I may ask, does anybody know the air-fuel ratio used during lean-burn mode? If normal is 14.7:1 what does the honda engine use under this mode...

I'd like to set up something similar on my car during cruising if possible.
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