What is the lowest octane an RX8 can safely use? - Page 2 - RX8Club.com

Go Back  RX8Club.com > Series I Tech & Performance > Series I Tech Garage
Reload this Page >

What is the lowest octane an RX8 can safely use?

Notices
Series I Tech Garage The place to discuss anything technical about the RX-8 that doesn't fit into any of the categories below.

What is the lowest octane an RX8 can safely use?

Old 03-14-2006, 06:59 PM
  #26  
脾臓が痛みました
 
Glyphon's Avatar
 
Join Date: Mar 2005
Location: Land of Peaches, Pecans, and Peanuts
Posts: 1,527
Thanks: 0
Thanked 0 Times in 0 Posts
to head off the questions about 98 octane...that's 98 RON, which is equivilent to 92/93 octane here in the states.
Glyphon is offline  
Old 03-14-2006, 06:59 PM
  #27  
Registered
iTrader: (2)
 
Easy_E1's Avatar
 
Join Date: Sep 2005
Location: Bellevue WA
Posts: 7,675
Thanks: 0
Thanked 4 Times in 2 Posts
I use 91 in my 8 and it runs great.
The wife put in 87 from the same station and it knocked like a bunch of vacumn cleaner salesman at the front door. It was a bad sound.
But it was summer here in Arizona and probably about 110 degrees.
That I feel plays a big part in the octane used.
All I know is that I will never put anything under 91 octane in my car here in AZ.
By the way I use QT gas which is a "Top Tier" according to BMW and Honda.
Easy_E1 is offline  
Old 03-14-2006, 07:07 PM
  #28  
Registered Lunatic
iTrader: (1)
 
Tamas's Avatar
 
Join Date: Aug 2003
Location: SF Bay Area, California
Posts: 3,475
Thanked 11 Times in 10 Posts
Originally Posted by Glyphon
to head off the questions about 98 octane...that's 98 RON, which is equivilent to 92/93 octane here in the states.
More like 94-95.
Tamas is offline  
Old 03-14-2006, 09:36 PM
  #29  
Registered User
 
Join Date: Apr 2004
Location: Australia
Posts: 88
Thanks: 0
Thanked 0 Times in 0 Posts
Just remember that the renesis is prone to carbon buildup. Most of the higher octane fuels have extra additives and detergents to clean you combustion chambers and plugs etc to prevent this build up.I feel that the extra expense for this feature alone is well worth it.
Regards
Rexi
rexi is offline  
Old 03-15-2006, 12:49 AM
  #30  
Registered
Thread Starter
 
swiftnet's Avatar
 
Join Date: Nov 2003
Location: Sunny Florida
Posts: 203
Thanks: 0
Thanked 0 Times in 0 Posts
Thanks to everybody who responded, for me it is not a money issue, the car just seems to run better (seat of the pants meter) on 91 vs 93 octane. I'll try the 89, and see how it goes. To all the 87 octane people, what is your avg gas mileage?

TIA,

Alex
swiftnet is offline  
Old 03-15-2006, 08:48 AM
  #31  
Registered User
 
Jaguar_MBA's Avatar
 
Join Date: Aug 2004
Location: Des Moines, Iowa
Posts: 495
Thanks: 0
Thanked 0 Times in 0 Posts
https://www.rx8club.com/showthread.p...ghlight=octane

Read the 3rd and 4th posting from the above thread....by MazdaManiac and Rotarygod.
Jaguar_MBA is offline  
Old 03-19-2006, 12:18 PM
  #32  
Registered User
 
needmorerotors's Avatar
 
Join Date: Dec 2005
Location: Las Veags
Posts: 59
Thanks: 0
Thanked 0 Times in 0 Posts
Where are you guys from tha has 93 octane at the pump.Here in cali the highest is 91.Also what the highest octane you run without engine damage or execeve wear.I want to know for when I take it to the track and would it help
needmorerotors is offline  
Old 03-19-2006, 02:57 PM
  #33  
Mean Green Keeny Machine
 
aggietiff28's Avatar
 
Join Date: Sep 2004
Location: NRH
Posts: 265
Thanks: 0
Thanked 0 Times in 0 Posts
I have run 87 octane a couple of times in the car and it gets "slightly" better gas mileage than with the higher octanes, but I can definitely tell that there is a power loss between 91 and 87, harder shifting, and more engine vibration. I can even tell the difference between 89 and 91. Maybe it is just my imagination, but I don't think so. I have one of the early build dates. Possibly that is why. I run 89 when I am feeling cheap and 91 when I am feeling sporty. Average between the two is just under 18mpg.

And remember, if you are concerned about carbon build-up in the engine...rev it every now and then to the beep.

Last edited by aggietiff28; 03-19-2006 at 03:00 PM.
aggietiff28 is offline  
Old 03-20-2006, 11:07 AM
  #34  
Registered User
 
Join Date: Oct 2005
Location: Ohio
Posts: 72
Thanks: 0
Thanked 0 Times in 0 Posts
Originally Posted by Easy_E1
I use 91 in my 8 and it runs great.
The wife put in 87 from the same station and it knocked like a bunch of vacumn cleaner salesman at the front door. It was a bad sound.
But it was summer here in Arizona and probably about 110 degrees.
That I feel plays a big part in the octane used.
All I know is that I will never put anything under 91 octane in my car here in AZ.
By the way I use QT gas which is a "Top Tier" according to BMW and Honda.
I was running QT when I lived there as well. I went down to the 89 and never had any difference. Even ran 87 from time-time. In the summer when they kick into the blend then definetly I would run the 91 but once they change over then you should be fine with 89 or so. But I miss the AZ year round climate!!
modforce is offline  
Old 03-20-2006, 11:45 AM
  #35  
shaaaaaa...
 
RX-Aight's Avatar
 
Join Date: Apr 2005
Location: Charlotte, NC
Posts: 297
Thanks: 0
Thanked 0 Times in 0 Posts
I think one of the only problems is excessive carbon build up from running lower octane
RX-Aight is offline  
Old 03-20-2006, 11:49 AM
  #36  
Registered
iTrader: (1)
 
Join Date: May 2003
Location: PA
Posts: 3,753
Thanks: 0
Thanked 0 Times in 0 Posts
to put things into persepective, i've been running on 89 octane with a cz tuned to 13.0:1 afr and upwards of 6 additional degrees of ignition advance for 1.5 years now without a problem
r0tor is offline  
Old 03-20-2006, 01:13 PM
  #37  
Lubricious
 
Nubo's Avatar
 
Join Date: Oct 2003
Location: SF Bay Area, California
Posts: 3,423
Thanks: 0
Thanked 1 Time in 1 Post
Well, I have officially changed my tune on this subject. Replaced plugs this weekend. Based on the condition of the plugs (2 years, 14,000 miles) I would say that higher octane is warranted, at least in my case.
Nubo is offline  
Old 03-20-2006, 01:28 PM
  #38  
Mulligan User
iTrader: (1)
 
ZoomZoomH's Avatar
 
Join Date: Jan 2003
Location: caddyshack
Posts: 4,612
Thanks: 0
Thanked 0 Times in 0 Posts
and what is the condition of your old plugs that led you to this new assessment??
ZoomZoomH is offline  
Old 03-20-2006, 01:29 PM
  #39  
Registered User
 
Brice-RX8's Avatar
 
Join Date: Feb 2005
Location: Winston-Salem, NC
Posts: 882
Thanks: 0
Thanked 0 Times in 0 Posts
Originally Posted by RX-Aight
I think one of the only problems is excessive carbon build up from running lower octane
This should be quite the opposite, the lower octane will "explode" and burn faster for a more complete burn. The 93 octane will actually burn slower and if the rotary is not able to get a complete burn there is where your carbon buildup will come from.
Brice-RX8 is offline  
Old 03-20-2006, 07:13 PM
  #40  
shaaaaaa...
 
RX-Aight's Avatar
 
Join Date: Apr 2005
Location: Charlotte, NC
Posts: 297
Thanks: 0
Thanked 0 Times in 0 Posts
Originally Posted by Brice-RX8
This should be quite the opposite, the lower octane will "explode" and burn faster for a more complete burn. The 93 octane will actually burn slower and if the rotary is not able to get a complete burn there is where your carbon buildup will come from.
yeah but doesn't that only matter engines that aren't high compresion?
RX-Aight is offline  
Old 03-20-2006, 07:48 PM
  #41  
The burninator
 
alcimedes's Avatar
 
Join Date: Aug 2005
Posts: 410
Thanks: 0
Thanked 0 Times in 0 Posts
High octane is more likely to cause carbon build up. More so than lower octane. Low octane (assuming the ECU is OK with it) should give you better gas milage, more power and less carbon buildup.

Cars that are tuned to high octane can compress what's injected into the combustion chamber further without preignition, giving you more power. Where the RX8 falls out between these two choices I have no idea.

Although it would be interesting to reset the ECU and run it on both types of gas. I know when I did I saw zero difference between the three tanks of gas of low and high octane. The only real difference I've ever seen was running nonoxy fuels vs. oxygenated fuels. The nonoxy was a considerable boost, and an additional 2 - 3 mpg more.
alcimedes is offline  
Old 03-20-2006, 09:58 PM
  #42  
Lubricious
 
Nubo's Avatar
 
Join Date: Oct 2003
Location: SF Bay Area, California
Posts: 3,423
Thanks: 0
Thanked 1 Time in 1 Post
Originally Posted by ZoomZoomH
and what is the condition of your old plugs that led you to this new assessment??
Spalling of the center insulator nose; a classic sign of detonation. I found this condition on both leading plugs; although the one in this pic was the worse. The ground electrode was intact but I removed it for the pic.

The car was running ok for the most part but had developed a mild stumble in stop-and-go traffic. It's running smoothly again now on the new plugs. My ghetto compression test (coasting down a long, steep hill nearby in 2nd gear) yields the same terminal velocity of 34 mph that it always has.
Attached Thumbnails What is the lowest octane an RX8 can safely use?-plug.jpg  
Nubo is offline  
Old 03-20-2006, 10:14 PM
  #43  
Zoom-Freakin'-Zoom
iTrader: (5)
 
swoope's Avatar
 
Join Date: Jan 2004
Location: orlando, fl
Posts: 14,582
Thanked 22 Times in 19 Posts
87 octane here for 43k miles. and my car was the one that scott at mazsport beat up.

about every 15k miles i run a can of b&g 44k in the tank.

my plugs were like *** a 30k miles. replaced free....

btw. my mpg average is over 21 mpg.

beers
swoope is offline  
Old 03-22-2006, 09:19 AM
  #44  
Registered User
 
Brice-RX8's Avatar
 
Join Date: Feb 2005
Location: Winston-Salem, NC
Posts: 882
Thanks: 0
Thanked 0 Times in 0 Posts
Originally Posted by RX-Aight
yeah but doesn't that only matter engines that aren't high compresion?
No that is the nature of gasoline, not the motor. All octane does is make gasoline more stable at higher compression and heat, which in turns means it will burn slower, the higher the octane. If you have a low compression car then you have no need for slower burning fuel (high octane). Some people's 8's run just fine on the lower octane (mine does) and gets better gas mileage than if I use 93, but others have problems using the lower stuff, just depends on the car. Remember also that the combustion chamber of a rotary is much different than a piston engine, so 10:1 on a piston engine seems to be a little different than 10:1 on a rotary, and I think it has to do with the shape of the chambers. Someone correct me if I am wrong.
Brice-RX8 is offline  
Old 03-27-2006, 03:21 AM
  #45  
The game changer!
 
T-von's Avatar
 
Join Date: Oct 2002
Location: Tx
Posts: 297
Thanks: 0
Thanked 0 Times in 0 Posts
Ok you guys are waisting your time and actually doing more damage by running higher octane fuel in a NA rotary. Some of you just don't understand how thermally unefficient the rotary is when it comes to fully burning the fuel air mixture. All higher octane gas does is burn slower. The slower burning process decreases the chances for detonation/knock. The side effect is the remaining unburned fuel turns into even more carbon deposits. More carbon just lowers your compression because the internal seals will start to stick. Why do you guys think you keep flooding so much? Flooding is a direct result of carbon infested engines.

Stop worrying about detonation so much. The Renesis is NA. Detonation on a NA rotary isn't know where near as bad as detonation on a boosted rotary. Between the two, there is a huge difference between the internal combustion pressures/detonation events inside the engine. There are guys running PP NA rotaries making 300 hp and running 87 octane. I personally run 89 octane in my Fd which is boosted and it has 103,000 miles on the original engine. You have nothing to fear. Ideally what you want to do is run the the fastest/cleanest burning fuel you can in a NA rotary. 87 octane burns faster and most importantly MORE FULLY. This is what the Renesis needs.

Last edited by T-von; 03-27-2006 at 03:24 AM.
T-von is offline  
Old 03-27-2006, 09:18 AM
  #46  
Registered User
 
Join Date: Sep 2003
Location: Liberty Hill, TX (Austin)
Posts: 886
Thanks: 0
Thanked 0 Times in 0 Posts
That sums it up. The Engineers at Mazda have no idea what they are doing.
Chrisbert is offline  
Old 03-27-2006, 10:01 AM
  #47  
Registered User
 
Brice-RX8's Avatar
 
Join Date: Feb 2005
Location: Winston-Salem, NC
Posts: 882
Thanks: 0
Thanked 0 Times in 0 Posts
Originally Posted by Chrisbert
That sums it up. The Engineers at Mazda have no idea what they are doing.
No, they do know what they are doing, they know how to market a sports car that is all. Recommending Premium fuel is a marketing strategy now-a-days where if you have to put premium in the tank it must be better. Notice Mazda "recommends" premium, they do not "require" it.

It has also been said over and over some 8's love the 87 and some hate it and love 93. My suggestion is try 87 and if the car runs good on it (mine likes it more than 93) then run it, if not go back to premium.

One last point, at least with my car, it feel much better on 87 than on 93, but putting a bottle of Techron in it every so often makes it idle so much smoother for some reason, and it is only with the Techron additive.
Brice-RX8 is offline  
Old 03-27-2006, 10:33 AM
  #48  
Registered User
 
Join Date: May 2005
Posts: 312
Thanks: 0
Thanked 0 Times in 0 Posts
i ran with a few tanks of 89. I feel no difference from 93 but psychologically I still worried about running 89 in the long run.
Animagix is offline  
Old 03-30-2006, 10:44 PM
  #49  
Registered
Thread Starter
 
swiftnet's Avatar
 
Join Date: Nov 2003
Location: Sunny Florida
Posts: 203
Thanks: 0
Thanked 0 Times in 0 Posts
Tried 87 octane...NEVER AGAIN!!!!

Sorry about shouting, but ****... I filled up with 87 octane, to see how the car would run. As soon as I hit 5Krpms the engine rattled (very ugly sound) and lost power. I kept the rpms below 4K and went staight to Discount Auto Parts, to pick up octane booster. After I added the octane boost the car ran better but still rattled at 5Krpm.
After I used 1/2 a tank (running at 4k or less), I filled up with 93 octane and the car is fine now. The gas was Shell (both the 87 and 93). The car runs fine with 91, and 89 seems OK, but for now, at least with my 8, 87 is just plain evil.

Cheers,

Alex
swiftnet is offline  
Old 03-31-2006, 09:49 AM
  #50  
Registered User
 
Join Date: Jun 2002
Location: Misinformation Director - Evolv Chicago
Posts: 3,086
Thanks: 0
Thanked 0 Times in 0 Posts
I ran mine on 93 for the first 10K. Since I figured the computer had learned on 93, I slowly backed it off to 87. Now at 22K, and for the last 12K, my car has run fine on 87. Maybe try it gradually.
Red Devil is offline  

Thread Tools
Search this Thread
Rate This Thread
Rate This Thread:
You have already rated this thread Rating: Thread Rating: 0 votes,  average.

Quick Reply: What is the lowest octane an RX8 can safely use?


Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

© 2019 MH Sub I, LLC dba Internet Brands

We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites.