Since 35000 mile service S8 is averaging 20 mpg vs 16 before! Unless they have pulled ..
06-12-2008, 08:56 AM
#14
AudiWorld Super User
Remind me on your offset again
Or said another way, would you still have the same clearance issue with the factory 46mm, if you could mount these on 9" rims which I realize are a bit narrow for 285s.
06-13-2008, 06:42 AM
#18
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There are strategies for attaining leaner mixtures
Stoichemetric ratio is not always possible due to shortcomings in the monitoring system. So the auto manufacturers develop strategies to run leaner than the O2 sensors indicate.
The stoichemetric ratio of 14.7 is driven by emissions as apposed to efficiency. I'd bet geordie's car is running significantly leaner than 14.7:1. It's probably also not meeting it's nitrogen oxide emission limits.
The stoichemetric ratio of 14.7 is driven by emissions as apposed to efficiency. I'd bet geordie's car is running significantly leaner than 14.7:1. It's probably also not meeting it's nitrogen oxide emission limits.
06-13-2008, 07:05 AM
#19
AudiWorld Super User
I guess that if the lambda probes were immediate in their reaction and alteration of fueling....
then it would be possible but because they are reactive they will always be slightly behind what the engine actually needs.
I guess they are spot on if driving at constant speed with the engine at full working temp. If you take the average of slightly lean mixture for the first few milliseconds of acceleration and rich for a short time upon a closing throttle then it must average out quite well.
I would suspect the actual mixture is set below the 14.7:1 to allow for higher than perfect fuel temp and a small amount of unburned oxygen around the perimeter of the combustion chamber which will never burn regardless of how much fuel is available.
If combustion were perfect why do we have cats? - so there mst be plenty of room for further reduction in the amount of fuel pumped in.
I would be a millionaire if I could find a way of ensuring complete combustion because it would provide a significant improvement in emmisions and economy.
I guess they are spot on if driving at constant speed with the engine at full working temp. If you take the average of slightly lean mixture for the first few milliseconds of acceleration and rich for a short time upon a closing throttle then it must average out quite well.
I would suspect the actual mixture is set below the 14.7:1 to allow for higher than perfect fuel temp and a small amount of unburned oxygen around the perimeter of the combustion chamber which will never burn regardless of how much fuel is available.
If combustion were perfect why do we have cats? - so there mst be plenty of room for further reduction in the amount of fuel pumped in.
I would be a millionaire if I could find a way of ensuring complete combustion because it would provide a significant improvement in emmisions and economy.
