High test vs Regular?

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gfield
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Joined: Tue Nov 09, 2004 11:04 am
Location: Northern Jersey

High test vs Regular?

Post by gfield »

Does anyone have hard data on running a car on 93 octane vs. lower octane/87? I know BMW recommends 91 or higher. But what does it really do or matter? Plus how about for cars other than a BMW what difference does it make?

Greg Field
1997 Boston Green M3 Coupe

dngo
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Re: High test vs Regular?

Post by dngo »

If your car is designed for 91 or higher octane (which your M3 is), then you will see several issues with moving to lower octane. Higher performance engines that have high compression (like your S52) or are forced induction depend heavily on fuel quality to achieve maximum performance.

1. Timing will be retarded to prevent knock, which will affect how much power the engine will produce. Most modern engines can handle lower octane fuel safely, but if you have a tune or the knock sensors are not working correctly, you can damage your engine.
2. You will see lower gas mileage. This can offset a significant amount of the cost savings in regular vs. premium fuel.
3. Higher octane fuel frequently has more additives (detergents, etc.) than lower octane fuel, which help things like minimizing carbon deposits.
4. BMW will come take its car back.

Other cars which are designed for 87 octane don't have these issues.
'15 MCR P90D <- the stealthy daily
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RAYADAM
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Re: High test vs Regular?

Post by RAYADAM »

Lot of people believe that high octane fuel is more "powerful" , it's not. Higher the octane number ,the less likely to knock(or ping) like Dave said above.high compression can cause fuel combustion too premature causing early detonation,higher octane minimizes this possibility . This allows the engine ECU to advance the timing to the most efficient and powerful levels for best performance. Modern ECUs can adjust on a wide scale but for some perceptive individuals,they can feel the power to the pants penalty.Also using too low of octane fuel can also increase fuel consumption(need to step on gas a bit more depending on vehicle). Most importantly ,turbocharged cars .BMW is running approx 10.5 to 1 compression(some engines even higher!) in there force induction cars,that insanely high in 1980-90's standards!
Ray
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2018 Shelby GT350

andypot1985
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Joined: Wed Jan 30, 2013 9:23 am

Re: High test vs Regular?

Post by andypot1985 »

Aside from everything already said, I switched to 93 octane years ago in all my cars. When I made the switch in the car I was driving at the time I saw much better results from oil changes. I could go more miles between changes and the used oil would be a much lighter color.

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