I know the manufacturer recommends premium. Says it on the gas cap, right? But what is the final answer?

 

I use premium. Gas is expensive either way so what the hell. Thats what everything I read calls for.

 

check Manual. 91 recommened.

 

premium.
Some people put 87 or 89, but premium is definitely the preferred way to go.

 

Lots of threads on it. Try searching "gas octane". I wouldn't use lower than 89; however, I put 91 in my car with a product called FP60 so I don't have to bother with premix.

I'm sure the engine computer knows what octane is in there and adjusts the engine accordingly.

 

I use 93...hurts the wallet though!

 

I've experimented with various octanes (87, 89, 91, 93) over the past 2000 miles since I've owned the car, and can tell absolutely no difference in performance or starting. I have noticed a direct inverse correlation between octane and gas mileage - I consistently get 1.5 - 2.0 mpg more with regular 87 octane.

The physics of this makes sense as well. Regular gas actually has more "energy" than premium (more carbon-carbon chemical bonds to break in the combustion process, and therefore more power to be released in burning a given quantity of fuel). The higher octane premium fuels are for high compression engines, with the extra octane used to prevent detonation and pre-ignition, which thus lets the engine run more advanced spark timing and therefore get more power output.

But, the rotary engine is inherently not a particularly high compression, or thermodynamically efficient, engine. The combusion chamber in the rotary is long and narrow, which is not thermodynamically the most efficient shape (which is why our cars use more fuel and get lower gas mileage than comparable reciprocating piston engines). Unless a rotary engine is modified with forced induction or otherwise has its compression ratio increased, it inherently should run fine on regular fuel. Rotary engines are used in some third world countries specifically for that reason, because they are less sensitive to octane, and can run fine on the lower grade fuels often available there.

Premium high octane fuel will minimize any risk of pinging or detonation, but these are probably not high risks in a rotary (and engine timing will automatically adjust to prevent it anyway). So, for me regular gas works fine (I refuse to be sucked in by the oil company advertising of premium fuel being the "good stuff", and don't want to unnecessarily contribute to the Exxon-Mobil corporate executive retirement fund any more than I have to...)

 

There is no final answer. I did a LOT of reading here on that very topic when I first got here, and as far as I was able to glean, there simply is no concensus. In particular, there was one thread that had a poll, where roughly the same number of people voted that they got better performance or mileage with regular as who said they got worse. The answers were just all over the map. I just gave up at that point. I continue to use premium, because, in the absense of any clear consensus, it seems the safest choice.

 

I have put over 520K miles on Mazda rotary engines. The answer is use the lowest octane your engine can run without pinging MIAC(Marble In A Can). My 8 will not run on reg-87 when its in the 60's F or above, but runs fine on mid-89 or prem-91. So its cheaper to run in the winter. This engine has higher compression and is more computer controled. If you run prem-fuel all the time you will be safer.

 

I have been using regular for the last 20,000 miles it is about to turn 30,000. It runs perfect for me, never saw a difference with premium and I get 19 to 23 miles to the gallon. I don't baby the car I frequently redliine it but usually not more than half throttle, just takes a little longer to redline.

 

I always use premium. I figure no matter what...if it's going to cost me a lot to fill it up, I might as well go with what the manual recommends

 

Traditionally, 93 vs. 87 is only and additional $0.20/gal. If you fill up 12 gallons, we're talking an additional $2.40 per fill-up and if you find the stations that have the 91 octane, then it's usually $0.15/gal more than the cheapest gas. Unless there's definate proof that 87 / 89 is good enough, I personally think it's worth the money.

 

This has been discussed many times and the people in the know pretty much state that if the car is not ping with 87 then go with it. The only thing that 91 or better will do if your not pinging with 87 is drain your wallet quicker.

I've been running 87 since I bought the car, tested high octane without any positive effect. The rotary by design runs better with lower octane and the manual say it can be used.

 

Until recently I' ran Premium. After getting the new flash I've been running 10 gallons 87 then 3 gallons 93. Runs just fine. It's not a linear difference and works out to about 90 octane. Sure I may be a little cheap but I fill it and the CX7 once a week - and do that in both tanks.

 

When I first got my 8 I ran strictly 93 octane. Then gas prices started to raise and I decided to try 87. The 87 did and still runs fine. It is cold still here in PA so I'm not sure how it does when it gets warmer but when the weather is cooler then it runs fine. I did notice a little performance difference above 7000 RPM but I expected that with the lower octane. I say if it's not making any odd noises with 87 run it. If it does make noises try 89. good luck

 

I use 93 at all times.

-Cody

 

 

Remember one ping in a rotary can mean blown apex seal

 

Your title is misleading.

Search is helping.

Its your lack of decision-making skills is what is slowing you down.

 

I used to run 87 (almost 3 years) with no problem until the latest recall flash. After the flash I started to experience pinging. Switched to 93 octane and the pinging stopped. I've tried 87 a few times since and had the same pinging problems. I'm sticking with 93 now.

 

Everyone.. THANKS A TON for your help. After further reading, all your posts, and more experimentation with the search, I will go with premium. I guess it won't cost me that much more, and I want to treat my 8 right! 91 is as high as I have seen in San Diego. And since it's usually pretty warm here (avg. about 70 degrees year-round) it seems safest to go with 91. THANKS!!

 

Yah - generally you want the highest octane you can budget.
There is sometimes power to be had with lower octane on a rotary motor, but its a dicey game.
Some have reported better mileage on lower octane as well, but who really cares about that.

The problem you face is that 91 in CA (and NV, AZ, OR, WA, NM, CO, UT, MT, ID and WY) is really 89 because of the balance of ethanol and additives.

 

Wait, what?

 

i use to run 87 all the time myself but when i bought a motorcycle, i pretty much stopped driving the car so i then went to 93 since i might put 20 or 30 miles on the car a week.

 

Higher octane = better combustion resistance. 87 burns easier than 93. That's why 93 protects against pre-detonation better than 87.

Some vehicles claim more power on high octane, but that usually means that the ecu changes fuel and ignition maps to better utilize the higher ping resistance. There's nothing magical about higher octane gas, it just allows for more aggressive tuning.

My car dislikes 87. I'm sure some high quality, freshly delivered 87 might work, but that's too much hassle and worry. So it's usually 89 in the cold, and 93 the rest of the year for me.