Octane Rating?
 

just got a new 06 phantom blue rx8, mazda recommends premium...anyone have any recommendations for actual brand of gas? ie chevron techron, or shell vpower?? any differences?? please help!!

Doesn't matter, it depends on the gas station too. You probably won't notice anything, just use 93.


Umm...posting pics should be your first priority.

Welcome to the forum! Although Mazda recommends premium for top performance, they also indicate--maybe imply is a better word--that lesser grades can be used but a drop in performance may result. A few members have reported pinging when using the lesser grades. I use Shell V-Power 93 octane, but I don't put a lot of miles on my car so fuel cost is not a major consideration.

There are many, many threads dealing with the grades and brands of fuel other members are using and recommending. Do a forum-wide search for the appropriate key words and you will find the answer to all these questions. In fact, you will undoubtedly find answers in the forum to just about any question you can come up with. Just search.

I use Sunoco, I think they have the best fuel quality wise.... The manual and the DVD they send you says use octane levels of above 91 which is premium, or they say you will see loss of performance... Since I've bought the car, I've only put in Premium.... Just to be safe I would follow their instructions....

Actually as long as you stay with one of the main brands, you're fine. It depends as much on the actual station, how clean their tanks are, etc. I've kept detailed records of my mileage from Day 1, and Shell 93 seems to work best for me.

Some have reported using regular unleaded is okay but I have also heard the pinging stories. Most of the Aussie owners seem to use either 95 or 98.

06 model year requires premium fuel.

I have actually done a little research on this, and what I have found was yes you will absolutely lose some performance using a lower octane, but you really should have no problems with a lower octane. In fact, I have found others who said they actually get better gas mileage with a lower octane, and I have been watching my gas mileage with different octane, and it does appear that the 8 will get better gas mileage with a lower octane gas.

Lower octane causes pinging in a lot of 8's.

I run 87 with out a problem. Don't waste money if you don't have to, Rotaries run better on lower octane fuel so if no ping 87 is the way to go.

so does 93, apparently

I thought they run better on higher octane.

I get better mileage with 91 and greater octane.

True in the old days, no today however. Most of the time you can run 87, but I have noticed pinging when the hot weather arrives.

Debate on whether or not loss of performance with octane, but I have never heard of an engine that runs better on lower octane. Some cars timing is set at 87 octane, and they got little improvement when they went to 91, but never worse. While I have seen cars with factory set timing to run best on 91 octane, and they lost substantial performance when they went to 87. Understand that the factory sets timing & timing range to run on a motor based on a specific kind/level of fuel. Imagine a range of 1 to 10. With a 91 octane recommended engine, with 91 octane it runs an 8, with 87 octane it runs a 1, etc. Now with an 87 octane engine with 87 it runs an 8, with 91 octane it might run a 9.

The reason why some of the engines are pinging is the engine can't retard timing any further, you are on the botom range of the timing and so detonation occurs because timing can't go any lower. Not good.

I can run 89 in the winter here in Pheonix.
But when the temp warms up in the 80's it is time to put in 91.
I can get some predetenation on 89 octane when the air is warmer.
So now it is Premium all the time.
And oh my GOD the wife put 87 in it one time and I almost had to have it pumped back out.
Never again.

Rotaries run better on lower octane! The reason for this is the long narrow combustion chamber. Higher octane is just a fuel that burns longer(slower) and is less susceptible to spontaneous combustion. The slow combustion of high-octane fuels works against a Rotaries long combustion chamber, you want a quicker burning fuel for these engines. I have read of Rotary race engines using octane under 85. The only time you are forced to use a higher octane is if you are getting pinging, if you're not getting pinging do yourself a favor and stick with 87.

Many people on this board with greater knowledge of Rotaries then myself have confirmed this and I have seen no one provided tested proof that their RXs runs stronger with 90 plus octane.

The RX-8 manual states you can use fuel as low as 87 octane.

Could you show an example? Many rx8 owners use the more expensive 91/93 because it is thought by most that it gives better performance.

Sorry I don't have a scanner handy but in my 05 users manual on page 4-2 here is the wording:

"You may use regular unleaded fuel with an Octane rating from 87 to 90 (91 to 95 RON) but this will slightly reduce performance."

I assume other years will have similar wording. In my manual page 4-2 is under the chapter titled Before Diving Your Mazda.

Yea, that contradicts what you're saying...?

first: I never heard of engin retard it-self, the higher the rpm the more advance the timing is. the only time engin retard it-self is when the knock sensor kicks in. :spank:
second: I will never try using lower octane on a rotary motor with such high compression ratio. :Eyecrazy:
third: I've seen too many RX-7 change motor because of pinging. :nono:

True, but what is a slight decrease 10 hp, 5 hp, .5 hp? Many Rotary experts on this board back up what I say and as many say power and mileage increase as do those who say it decreases with 87-octane fuel. Based on a lack of any proven statistics that show a power decrease with 87 octane I will listen to those in the know and trust my own experience.

I could be wrong but do a search on this subject and look at what Rotary God posted on it.

1 - Almost all modern cars have knock sensors that will retard timing if it sense pinging. This has been a feature of modern engines for over 10 years.

2 - I do every day.....no problems.

3 - Would these RX-7 engines belong to tuners who over boosted their engines? Don't confuse poor tuning with engine requirements. Additionally high boost turbos usually require higher octane. Last I checked the RX-8 didn't have a turbo.

Thread with some posts by rotarygod:
https://www.rx8club.com/showthread.p...ne+performance

Mr. All-Knowing basically says use whatever fuel you feel works best =/

Here's another...too many opinions regarding octane.
https://www.rx8club.com/showthread.p...ne+performance

I think I'm going to try 87 for a while and see how that goes. Maybe my pinging will go away that way!