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What is the lowest octane an RX8 can safely use?

Old 12-28-2018, 09:18 AM
  #101  
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Originally Posted by swoope View Post
and how good where the knock sensors before 2004?

i will say as at 140k miles on 87 street and 93 on track it has been all good.. note, if under cruise on the interstate 87 gets the nod for mileage.

beers
Swoope that includes my 2008 RX8. I just think to believe we know more about the proper care for the best performance and longevity of these engines, than the engineers who designed, built and tested them is simply foolish. Sure some modifications and running without emission controls can yield some rotary performance benefits but ultimately (especially with the already high-strung Renesis) any deviation from the recommended is playing with fire IMHO. It is fine if you disagree with me on that, but I have been around a host of these engines and seen them used and abused, torn apart and rebuilt and I do have an experienced perspective on this. Cheers
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Old 01-09-2019, 02:14 PM
  #102  
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Ah what the heck, why not bump this thread in 2019....

Iíve been a PREMIUM 93 + 0.5oz per gallon premix with Idimitsu kinda guy since I got my Series 1.

This thread got me thinking, so now I wanna try lowering the octane and see how she runs.

Mine has low compression @ 90-ish psi across the rotors, so itís no longer ďhigh compressionĒ. Lol. Wondering what the butt dyno will feel like.

Are there no concreate testing / dyno runs done on this subject to nail this coffin shut? Rotaries have been around since I was born and seems the debate is still going on. why hasnít anyone myth busted this crap yet? Iím shocked.
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Old 01-09-2019, 07:42 PM
  #103  
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Moderns cars with the piezoelectric ping deterctors will automatically adjust (advance or retard) the spark relative to the eccentric shaft position (or p-p-p-piston position in the cylinder) to prevent knock. When knock is detected (or you disconnec tthe knock piezoelectric sensor) the spark retardation "automatically" yields less power- hence your butt dyno should feel less power. However under certain conditions and compression knocking (pinging) may still occur - not good for any engine.

My knock sensor wiring became lunch for a varmint on my CRV and hence my engine has far less power now, especially when I need to accelerate quickly.

Oh - I use 91-93 octane regularly in the RX8 with some added thick, rich molassesy premix in the gas.
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Old 04-03-2019, 02:10 AM
  #104  
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Just thought Iíd leave my 2Ę here, but Iíve been running 87 (88 if at shell) for the last 3-4 months with zero issues in my 2010 R3. Iíve been premixing 0.5 Oz per gallon for most of the time until an oil analysis lead me to believe my OMPs (1 or both) May be failing and have increased my premix ratio to 1 Oz per gallon. Immediately after the switch from 91 to 87 (maverick gas) the car felt exactly the same and, over the next week and a few tanks, nothing changed. The car ran and drove exactly the same. I think the only difference that might play any part in why my experience has been different from others is that, right before the switch, I installed GM D585 coils and brand new plugs and had my battery disconnected during the install which resets the ECU being disconnected for more than 30 seconds and also resets fuel trims, so Iím lead to believe that the car relearning the fuel trims is what let the car adjust to the lower octane without issue. So for anyone that wants to switch, maybe just try disconnecting the battery for 30+ seconds and see how it goes.

With my R3 being my primary daily itís nice not having to spend as much on fuel, so thatís likely the only difference. Iím now beginning to wonder how 85 octane will do seeing as the Renesis is an NA rotary and all older NA 13Bs run best on the lowest octane available (such as my 1980 SA22C which runs 85 and 1 Oz of premix per gallon). I also doubt the higher compression ratio of the Renesis matters at all either, because if it did then the S5 NA 13B, which also works best on 85, would likely be in the same boat (9.7:1 vs the renesisí 10.0:1).
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Old 04-03-2019, 02:30 AM
  #105  
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Originally Posted by @italia916 View Post
Just thought I’d leave my 2Ę here, but I’ve been running 87 (88 if at shell) for the last 3-4 months with zero issues in my 2010 R3. I’ve been premixing 0.5 Oz per gallon for most of the time until an oil analysis lead me to believe my OMPs (1 or both) May be failing and have increased my premix ratio to 1 Oz per gallon. Immediately after the switch from 91 to 87 (maverick gas) the car felt exactly the same and, over the next week and a few tanks, nothing changed. The car ran and drove exactly the same. I think the only difference that might play any part in why my experience has been different from others is that, right before the switch, I installed GM D585 coils and brand new plugs and had my battery disconnected during the install which resets the ECU being disconnected for more than 30 seconds and also resets fuel trims, so I’m lead to believe that the car relearning the fuel trims is what let the car adjust to the lower octane without issue. So for anyone that wants to switch, maybe just try disconnecting the battery for 30+ seconds and see how it goes.

With my R3 being my primary daily it’s nice not having to spend as much on fuel, so that’s likely the only difference. I’m now beginning to wonder how 85 octane will do seeing as the Renesis is an NA rotary and all older NA 13Bs run best on the lowest octane available (such as my 1980 SA22C which runs 85 and 1 Oz of premix per gallon). I also doubt the higher compression ratio of the Renesis matters at all either, because if it did then the S5 NA 13B, which also works best on 85, would likely be in the same boat (9.7:1 vs the renesis’ 10.0:1).
But isn't 87 recommended for NA RX-7s officially? In that case, yeah just use 87.

Officially, Mazda recommends 91 for the RX-8 so that's all I have been using. I don't feel like taking the extra risk, and I floor it a lot, so I like having as much power available and no knock happening under full load.

NA RX-7s made, what, 160 BHP stock? RX-8 makes 232 BHP stock, so I would think the octane tuning would have something to do with that.
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Old 04-04-2019, 10:31 AM
  #106  
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The power the engine makes has nothing nothing to do with octane requirements. Some have even seen slight power increase with lower octane fuel on the dyno (no changes other than fuel). Mazda also recommends using only 5W20 oil in North America (this is very bad on bearings and can cause excessive wear). As for NA RX-7s most owners (including myself) have noticed the car runs much better on the lowest grade of fuel available.

The Renesis is an NA rotary engine just like the others. Mazda designed it no differently than any older engine aside from making the intake ports MASSIVE and moving the exhaust ports over. It shares rotor and stat gear bearings with the FD and has more oil injectors. The engine has differences, but still shouldnít be treated any differently as thereís no benefit to it. Premium fuel is just a waste of money imo because Iíve seen no ill effects from switching myself, the car performs exactly the same as before.



Originally Posted by UnknownJinX View Post
But isn't 87 recommended for NA RX-7s officially? In that case, yeah just use 87.

Officially, Mazda recommends 91 for the RX-8 so that's all I have been using. I don't feel like taking the extra risk, and I floor it a lot, so I like having as much power available and no knock happening under full load.

NA RX-7s made, what, 160 BHP stock? RX-8 makes 232 BHP stock, so I would think the octane tuning would have something to do with that.
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