2007 Mazda RX8 and 87 Octane Fuel

The owners manual sayes gotta have 91 octane, but some people say they use 87 with no issues. I read about the dangers of knocking but would the engine really die if I a fuel with an 87 or 89 octane rating?

If I am interpreting this post correctly, the OP bought a car that requires 91 octane, and now, a few months later, decides that he wants to run it on gas that is of an octane rating lower than is required by the manufacturer.

That being said, my response includes a question:

Q: Will it die?
A: No, not immediately.

How long are you planning on keeping this almost-new car that you plan to run on fuel of too low an octane?

all i call thick of is to try it and hear if it pings. try running your tank down and put a little bit of 89 and drive it around and lison to if it pings. if it dose go to a gas station and full it up with 91. if it dosen’t ping kepp putting 89 in. it’s a little cheaper and you will only lose a bit of performance. most new cars have anti ping sensors. so it pulls back your timing.

hope this is helpful

mopar man

All modern cars have knock sensors that will prevent lower grade fuel from causing the pre-detonation problems (knocking) that will damage the engine, but it does this by retarding the ignition timing. What you get is less performance and carbon build-up due to incomplete combustion. The reduced performance will also show in lower MPG numbers. And, carbon build-up will haunt you later on with continued reduced performance even if you try to switch back to the proper grade. All this for saving $1-3 dollars per fill-up. Is it really worth it?

All of the car makers put out bulletins on the harm done to engines and engine performance when an octane fuel they don’t stipulate (either “recommended” or “required”) is used in their engines. Who knows these engines better than the car maker’s engine engineers, who live and breath these engines every day?!

The poster wasn’t the purchaser of the car, it belongs to his wife. I drive a CRV honda because I mountain bike, paddle a kayak and race bmx bikes so the RX8 does not fit my lifestlye. However, while looking into this isuue for my wife some posters on the site “RX8Club.com” use 87 octane gas and have gotten better gas mileage and have noticed thier exhaust doesn’t smell like unburnt gas. So if you have any real experience with the issue I’d like to hear it. I remember Tom and Ray answering a similar question and never brought up engine damage, but talked about a slight loss in performace, saying most wouldn’t even notice it.

Most of the discussions surrounding this issue deal with the effects of lower-than-recommended-octane gasoline in PISTON engines. The RX-8 has a Wankel rotary engine. This engine (and especially the tip seals) may respond to lower octane gas differently.

If this were my car I’d feed it 91 octane or sell it. When the owner’s manual says “91 is recommended,” that’s one thing, but when it says “91 is REQUIRED,” you should do what the manual says. It’s your car, do with it what you want. The RX-7 I owned a few years back got nothing but premium.

When it concerns octane, or some other issue, somebody always trots out Tom and Ray as ultimate authorities. You have added an RX8CLUB.com site to the list.
The various bulletins issued, are by the car makers engineers. I believe that they are the more qualified experts.

H& mpccullen

I don't think you can use the ping test on a rotary engine.


Consider this.  If Mazda has designed and built that engine and if they say it needs 91 octane, I would use it.  

I fear that you are not going to find much real information on what happens long term with that engine using regular outside of Mazda.  Most post here are based on piston engine results.  I suspect that they are going to be similar in the Rotary but I really don't know.  I personally would not want to find out the hard way.  

BTW I had a RX-7 and loved it.  The feel of that engine is great. It also handled fantasticily.

LOL, don’t make me laugh no more… But here the math, do it yourself, you’ll see. on 87 you get less miles to a gallon, cause it will take more fuel to combust. On 93 it’ll tale less fuel to combust. What i’m saying is on 87 gas, you’ll be on the pedal deeper to go. On 93 it’ll be less. So you will be ending up the same. I studied that by reset my trip meter everytime i fuelled up. And saw the numbers. Even my VAN ran on 93

I drive a 2004 RX-8 as one of my primary drivers . . . the other is an 89 Accord. My experience with using 87 in the rotary is that my mpg dropped, not a great deal, but 3-5 mpg. I never noticed a “ping” or other noise when using the 87, and only used it to test the suggestion that you can run the RX-8 on a lower octane fuel. My conclusion is that you CAN run on it, that you WILL get less mpg, and that you may VOID the warranty if you ruin the engine while using it. I generally get 28 mpg on 91, and got 23-25 on 87. I only did this to prove it to myself, two or three tankfulls, certainly not a scientific study . . . but enough for me. The owners manual says " You may use a regular unleaded fuel with octane rating from 87 to 91 (91 to 95 RON) but this will slightly reduce performance. It could also cause engine knocking and serious engine damage." The sticker on the fuel filler door also says" premium recommended". This is somewhat contradictory . . . you may use it but it could cause serious engine damage? I certainly don’t want to replace the engine on this car . . . big $$$$. In my area 87 is only 20 cents less per gallon than premium . . . my tank holds 16 gallons (15.9 actually) . . . and I usually fill-up with 10 or so gallons, never allowing it to run down beyond a quarter tank. Two extra bucks per tankful . . . per week for me, isn’t a burden. Now . . . the real question . . . ISN’T THIS CAR A BLAST TO DRIVE? Don’t you just love it? I do! Zoom-zoom! Rocketman

I also carry a bottle of octane boost in my trunk and use it whenever I can only buy 87 octane. Sometimes you can find this stuff on sale for less than $2 a bottle and I buy a few for just this reason. Rocketman