which is the best fuel for a rotary??
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Joined: Nov 2001
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From: Kenmore, NY
Per Felix's FAQ.
http://mrmazda.no-ip.com/cfaqtext.html#ROCTANE
What's the best fuel for my rotary car?
It depends. If your rotary Mazda is equipped with a turbocharger, all the normal rules about octane apply. Use the highest available octane premium fuel for best power and best protection against the ravages of detonation. You may find slighly better fuel mileage using lower octane, but you need to be very careful about using the available power on lower octane. If you are good at exercising restraint, you can save a little money on a long trip using regular, but it's probably best to stick with premium for normal use.
WIth the NA rotary, the highest octane you should use is US pump (AKI) 87, typically RON 91 outside the US, no matter how heavily your engine is modified. Octane in excess of any engine's actual requirement is always wasted. The issues of purity and additives in more expensive fuels are entirely separate issues. There's no reason not to want either in a NA rotary.
The rotary engine's high turbulence combustion chamber provides a very high resistance to detonation. Its duration of combustion is also longer, remembering that the rotors turn at 1/3 of the tachometer reading, and the slow burn* of high octane is undesirable in it. Pump 80 octane is more than sufficient for most of them. Best power and mileage are usually produced with the lowest available octane.
Many serious rotary racers bring their own low octane gasoline to tracks that supply only racing gasoline. From "How to Modify Your Mazda RX-7", by Dave Emanuel and Jim Downing, HP Books, 1987, ISBN 0-89586-383-9, p 47-8:
". . . the best results are obtained with conservative spark-lead calibrations provided the engine is fed a diet of low-octane fuel. The fact that both 1985 and 1986 IMSA Camel Lights championships were won with low-octane fuel is a rather definitive statement . . . ."
So if you want best performance from your NA rotary, you want lowest octane. The lower cost of it is a nice bonus.
* Note - the time allowed for combustion at high RPM is measured in ten-thousandths of a second. Some literature ascribes lower volatility rather than a slower burn as the characteristic of a higher octane value. In contrast, consider the following: From "14-to-1 compression", By David Green, NASCAR Winston Cup Scene:
"One problem that has developed in the 9.5-to-1 engine is high exhaust temperatures, due to a less-efficient burning of 108-octane gasoline in the lower-compression combustion chamber." (emphasis supplied)
For more information on octane/antiknock characteristic:
Octane Determination, by Gregory Travis
The autos/gasoline FAQ, by Bruce Hamilton, or its mirror.
Chevron's "A Consumer's Guide: Gasoline Octane for Cars"
Mobil's "Gasoline Product Knowledge"
http://mrmazda.no-ip.com/cfaqtext.html#ROCTANE
What's the best fuel for my rotary car?
It depends. If your rotary Mazda is equipped with a turbocharger, all the normal rules about octane apply. Use the highest available octane premium fuel for best power and best protection against the ravages of detonation. You may find slighly better fuel mileage using lower octane, but you need to be very careful about using the available power on lower octane. If you are good at exercising restraint, you can save a little money on a long trip using regular, but it's probably best to stick with premium for normal use.
WIth the NA rotary, the highest octane you should use is US pump (AKI) 87, typically RON 91 outside the US, no matter how heavily your engine is modified. Octane in excess of any engine's actual requirement is always wasted. The issues of purity and additives in more expensive fuels are entirely separate issues. There's no reason not to want either in a NA rotary.
The rotary engine's high turbulence combustion chamber provides a very high resistance to detonation. Its duration of combustion is also longer, remembering that the rotors turn at 1/3 of the tachometer reading, and the slow burn* of high octane is undesirable in it. Pump 80 octane is more than sufficient for most of them. Best power and mileage are usually produced with the lowest available octane.
Many serious rotary racers bring their own low octane gasoline to tracks that supply only racing gasoline. From "How to Modify Your Mazda RX-7", by Dave Emanuel and Jim Downing, HP Books, 1987, ISBN 0-89586-383-9, p 47-8:
". . . the best results are obtained with conservative spark-lead calibrations provided the engine is fed a diet of low-octane fuel. The fact that both 1985 and 1986 IMSA Camel Lights championships were won with low-octane fuel is a rather definitive statement . . . ."
So if you want best performance from your NA rotary, you want lowest octane. The lower cost of it is a nice bonus.
* Note - the time allowed for combustion at high RPM is measured in ten-thousandths of a second. Some literature ascribes lower volatility rather than a slower burn as the characteristic of a higher octane value. In contrast, consider the following: From "14-to-1 compression", By David Green, NASCAR Winston Cup Scene:
"One problem that has developed in the 9.5-to-1 engine is high exhaust temperatures, due to a less-efficient burning of 108-octane gasoline in the lower-compression combustion chamber." (emphasis supplied)
For more information on octane/antiknock characteristic:
Octane Determination, by Gregory Travis
The autos/gasoline FAQ, by Bruce Hamilton, or its mirror.
Chevron's "A Consumer's Guide: Gasoline Octane for Cars"
Mobil's "Gasoline Product Knowledge"
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The shop that tuned my car said they get excellent results from that fuel and it is very consistent. It is also one of the few pump gases with no ethanol.
However, the best gas for your car depends on what it was tuned for. If you car is pretty much stock with a Power FC 91 will be fine. If it is ported or single turbo I would want to find out what gas it was tuned on, or failing that, get a tune.
Better safe than sorry
For one ethanol is bad for our engines in the sense of the fuel system. We didn't have a fuel system designed with e10 in mind like mid 2000s cars did, and our fuel systems utilize rubber o rings, which are attacked by ethanol. Whether ethanol also attacks our coolant seals, someone more experienced would have to answer but it seems viable to me..
Last edited by nopistons1994; Jul 30, 2018 at 06:03 PM.
There are many that are ethanol free, check the map /info below. I just prefer Shell as that what my car was tuned to:
https://www.pure-gas.org/
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