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Re: Another question about octane... Posted by Ari [Email]  (#2847) [Profile/Gallery]
(more from Ari) on Wed, 16 Nov 2005 05:19:25
In Reply to: Another question about octane..., Alex S., Tue, 15 Nov 2005 13:11:25 Members do not see ads below this line. - Help Keep This Site Online - Signup |
You will get more performance from higher octane only if the lower octane fuel is limiting your engine due to knock. The engine control will make adjustments DOWN from optimal if it detects knock. But if the engine runs at full performance on 87, the engine control won't 'dial it up' if you put in 89.
You won't hear knock, because the engine control will prevent it. So you really can't tell without lots of instrumentation if the difference is subtle. As to what your car takes, I agree that the manual is a good start, but that value was picked to cover all the cars. Each car is different, and that changes as they age.
Will you get better mileage with higher octane? As others have said, theoretically lower octane fuel has higher energy content. Theoretically. IF the engine control has to compensate for too low octane, that will adversely impact fuel economy. If the engine control is just fine with 87, you'll get no advantage with higher octane.
It's difficult to determine fuel economy differences in fuel without instrumented test engine in a controlled test. Two trips back to back won't do it - fuel economy is strongly impacted by speed, air temp, traffic conditions, driving style, altitude, car load, etc. You can think you're driving just the same, but small differences are there.
Gas may not be a renewable resource, but when it comes to fuel milage, I think about how much it is costing me, not how much fuel I use. Where I live, 89 is about a 5% increase over 87; 91 is 5% higher than 89. So if it were just gas mileage, I would need to see a 5% increase in gas mileage to use 89. I don't expect you'll see that - I don't expect you'll see any change.
posted by 192.249....
, Wed, 16 Nov 2005 05:19:25 <-- Viewing This Message
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