Unleaded or Premium Fuel? (USA)
#21
01-24-2017, 10:58 AM
Senior Member
I got a question about this. If you had a car that didn't run very well on 87 octane, what would you suspect? I have one like that, and it's a lo-po non-turbo. I guess I need to hook up the scan tool and watch the ignition timing just for fun, but I sure wouldn't know what to do about it if it was in fact jumping around. So far I have figured buying premium is easier than trying to diagnose it.
#22
01-24-2017, 11:27 AM
it would be interesting to see the scan tool results on the ignition timing for 87 vs 93. If you think about what generally can cause pinking, theres- a lot of factors which can lead to unburnt fuel which can cause the problem... weak spark? intake system (air leaks, dirty MAF/ idle valve/ throttle body), carbon build up on pistons etc? I guess this is why Seafoam and other detergent treatments draw interest.
#23
01-24-2017, 12:25 PM
Senior Member
#24
01-25-2017, 01:27 PM
anecdotal evidence is not the same as science (correlation vs root cause). Sure some cars may run better on premium but that may actually be pointing to some other issues like a marginal state of tune like weak spark (look at all the threads where somebody reported dropping in new coils or plugs remarking "and the car is running like new"). There is a difference in the fuel's energy density (which is why diesels get higher mileage) but that is mostly due to the percentage of ethanol. Even "winter" fuels with up to 10% ethanol have only a 2% difference vs 100% gasoline or about .5 MPG. I do notice a difference summer to winter of 1-2 MPGs in my 850T, but I attribute much of that to temperature (parasitic losses not engine efficiency) and winter gas (that .5 MPG). I've run 87 and 93 and can only conclude the extra WOT power you get from 93 influences the driver's style not the car's performance.
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