Got shorted on gas at WAWA
10-23-2006, 10:10 PM
#16
Could be the refinery has to change the formula for cold weather driving. Here in the Tulsa area we get a formula change every fall and spring which affects most vehicles gas mileage. Also, the colder weather and a sticking thermostat can cause richer running.
Dennis
Dennis
10-23-2006, 10:33 PM
#17
Three Wheelin'
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Damn good point. I forgot about that.... I know they do it in CA, not sure if they do it up here in WA.. I generally have my foot so deep in the firewall it would not make much sense for me to try and track milage.. 
10-24-2006, 02:17 AM
#18
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Originally Posted by Jim bailey - 928 International
Ah...."The question is did they somehow fill the Super93 tank with Regular87? That would account for some lost milage." High Octane fuel simply put BURNS SLOWER it really does not carry more energy NOR does a car produce more power by using higher octane fuel than it was designed for. If
you burn alcohol it has significantly LESS power per gallon but better higher Octane rating which is one reason CART/ Indy Cars used alcohol. So when people get all excited about using corn to replace gasoline they need to factor in the fact they they need something like 40 % more alcohol by volume plus to fully explote the potential the engine should be built with much higer compression ratios to utilize the higher octane. I am not sure why your MPG varied but doubt it has much to do with the fuel and the comment that you buy your gasoline at the raceway does make me wonder what Octane Fuel you were normally burning ?
you burn alcohol it has significantly LESS power per gallon but better higher Octane rating which is one reason CART/ Indy Cars used alcohol. So when people get all excited about using corn to replace gasoline they need to factor in the fact they they need something like 40 % more alcohol by volume plus to fully explote the potential the engine should be built with much higer compression ratios to utilize the higher octane. I am not sure why your MPG varied but doubt it has much to do with the fuel and the comment that you buy your gasoline at the raceway does make me wonder what Octane Fuel you were normally burning ?
Never said higher octane had more power in the gas itself, but our cars are designed for high octane gas. In that case, using high octane gas WILL improve performance and mileage. The reason has to do with the compression and ignition timing characteristics of the engine. Our specially designed engines will only perform efficiently with higher octane gas. Even if he has no noticable "knock", igniting the fuel to early before TDC, can rob power and efficiency. You can retard timing slightly to offset the effect, however in a high compression engine as some 928's have, low octane gas will rob power and milage.
Also the ECM will kill some power to accomodate the lower octane. The ECM can monitor and control:- mass air flow, fuel
flow, ignition timing, exhaust oxygen ( lambda oxygen sensor ), knock
( vibration sensor ), EGR, exhaust gas temperature, coolant temperature, and
intake air temperature. The engine management system uses ignition timing as one of the major
variables that is adjusted if knock is detected. If very low octane fuels
are used ( several octane numbers below the vehicle's requirement at optimal
settings ), both performance and fuel economy will decrease.
Try running your shark on regular gas for a couple tanks, especially under hard accelaration, and check your gas milage. It's not that high octane gas has more power, it's that our engines are designed for it. If they doon't see it, they will kill power and milage to avoid knock.
10-24-2006, 03:48 AM
#19
Rennlist Member
Actually, my car was designed to run on 87 octane. Remember, gas was an uncertain commodity back then, one could not travel all over europe and be assured of high-octane availability. So, with my timing set to spec, I would not see any gain from higher octane fuel.
That's not to say it wouldn't be feasible to advance the timing and take advantage of higher octane though.
That's not to say it wouldn't be feasible to advance the timing and take advantage of higher octane though.
