Petscar

As recommended, ive been premixing with 91 octane which is the highest you can get in CO due to elevation.
i tried a couple of tanks on 85 and the car runs just as well as high test. Has anyone tried this? Mpg seems to be the same.

swoope

iTrader: (5)

you mean 87?

i have run 87 all my life in the rx8. except for track events. i also dont drive like a dick on public roads. you would be shocked that both the really smart rotary guys within a two hour drive say the same.

beers

mazdaverx7

iTrader: (6)

I've always run 87 in all of my rotaries other than the 8. Never gave it a second thought as it says to run premium in the car. I don't think it would hurt a thing to run 87 as long as you're not constantly beating on it.

Sydo

jakejm79

I believe in AUS (and Europe and likely other parts of the world) octane ratings are calculated differently so you can't compare straight numbers between locations.
85 is likely correct for CO since due to the thinner air at elevation and less oxygen per same volume of air vs sea level you can get away with lower octane fuel, well unless you run FI.
Its entirely likely that the ECU will adapt to whatever octane you have in your tank, you may not get the same level of performance or economy (but depending on your driving style you may not notice a difference). A lot of times the Manufacturer will spec premium fuel because that was what they required to make the advertised MPG or performance stats, not because your engine will blow up if you don't use premium.

Petscar

Jake, you are right. Due to elevation the air is thinner and octane requirements are lower. Our regular gas is 85. Our premium is 91 octane with mid grade being 87. As a result of the elevation, there is also a difference in performance. At least that is what i have been told. I would believe it is probably more noticeable in higher performance cars.

​​​​​​i found a bunch of threads where many use regular octane as opposed to hi test. Most seem to agree the rx runs just as well on regular. There were a few that didnt agree. I plan to keep trying regular with hi test every few tanks until i find a reason i shouldnt. In CO the difference in price can be 50 - 60 cents. Funny how in Utah i found that it was only a 10 cent difference between grades so regular to high test was only a 20 cent difference.

UnknownJinX

I have always used Shell 91 or Chevron 94 locally, more of the latter nowadays because Shell 91 gives me the rotten egg smell out of the tailpipe while Chevron 94 doesn't, and the price difference is about 1 dollar per tank. I also prefer using pure gasoline, which both of these gas are. No E10 gasohol crap.

Supposedly, according to the Owner's Manual, if you live in an area with high temperature or low humidity, then using anything below 91 can knock.

As for how much timing the RX-8 pulls and the amount of power reduced, this is something only someone with a dyno can answer. I know Ecoboost Mustangs make 320 BHP on 91, but only 260 BHP on 87, but it's a turbocharged car.

As for performance, I guess it should be enough for causual daily driving. I do more spirited daily driving, floor it a lot(when conditions allow, obviously) and like having a little bit more punch.

NotAPreppie

Nope. Nobody has ever tried this. Not ever. Never even been discussed before.

I suppose you could log timing retard due to knock in the ECU. I don't know if it works but should be mode 0x22 PID 1746.

jakejm79

This has been hotly debated for as long as there have been car forums and I don't think there will ever be anyway to really know (since the variables for engine failure are so wide), a lot of people have wrongly assumed that just because the manufacturer spec'ed high octane fuel that the engine will grenade itself it that isn't used or warranty service will be denied, neither is true.
I've heard stories of failures of engines (pistons specifically) at higher altitudes and people running on lower octane, but these were normally has a result of a MAF failure (would higher octane have provided that little extra headroom of knock protection to prevent the failure - who knows).

If you want to make sure get the Manufacture's claimed specs for MPG, HP, etc then use what they spec for the fluids/fuel, if you don't care and find the car drives fine without that then by all means put in whatever you feel like and don't lose sleep over it.

UnknownJinX

With a Bluetooth OBD2, I can monitor the timing on the trailing plug side only, not the leading side. I have read that a better unit could access PIDs.

NotAPreppie

If you're monitoring via a smartphone it's all about whether the dongle can speak CAN or just OBDII and whether the software supports custom PIDs or has these PIDs built in. IIRC, genuine ELM327 dongles can speak most versions of CAN but it'd be a crapshoot as to whether the cheap knock-offs do.
https://www.elmelectronics.com/products/ics/obd/
https://en.wikipedia.org/wiki/ELM327#Pirate_clones

I just bought the $9.99 2005 Mazda pack in OBD Fusion and it lists a ton of manufacturer-specific PIDs. I haven't had the chance to try any of them yet but the custom PIDs I added for tire pressure work using my Kiwi3.