Hi all,

I'm new here, but not new to rotary engines. I had an '84 GSL-SE (13b) several years ago. I was told by my mechanic who knew rotaries well that the normally aspirated rotaries liked low octane gas since the engine has a longer burn time and is a low compression engine. My 13b ran great (I used to race the thing) with regular gas. I tried premium, but noticed no difference.

So now I'm looking into an '06 and I read that Mazda suggests premium. Why? What has changed with the Renesis? Anybody have the answer?

Thanks!

Daniel

 

It prevents knocking...using a lower grade MAY cause knocking.

 

If you want your engine to last longer, use premium.

Well, not really but it helps in some way.. I wouldn't dare use regular on my 8.. Not even if I was outta gas and the only available octane was regular!

Plus, you go fast with premium..

 

Some have reported ping with 87 octane. I've used 87 octane for 40K+, and at the race track and have never had any issues.

 

maybe we should get some jet fuel and go intergallactic

 

Maybe cuz you really don't have a chance to listen for it...

 

we have higher compression rotors. mazda can't recommend different oil and fuel mixtures for different areas of the united states, so they give you the combo that will work the best for all regions. CA gas especially sucks.

I ran 87 without issue too.

 

I don't know what the earlier rotaries were, but the Renesis has a compression ratio of 10:1. That usually means you need more than regular. Mazda's spec is 91, not the 92 or 93 that (depending where you live) is the highest grade on the pump.

Because of engine sensors and electronic management, you can run most modern cars on lower than the recommended octane. The spark just gets retarded to avoid knock. Mazda requires at least 87, and recommends 91 for best performance. A lot of people here report using 87 and are very happy with it. Some report knocking if they don't use premium.

I use premium. Too low an octane might cost performance or (long shot, these days) damage the engine. The worst you can do using too high an octane is waste money. But if I was going to worry about that, I'd have gotten a car that got better than 18 mpg.

Ken

 

almost all cars on the road today (naturally aspirated at leaast) have a 10:1 or higher compression ratio. 90% - or more - of which recommend 87 octane. You think all the crappy civics and corolas, explorers and jeeps use premium?

its all about the tune.

 

Recently I have switched to 89 from 93 and noticed gas mileage is a little better as well as performance better.

 

must be placebo effect, you will get better mileage with lower octane because it's retarding the timing.

 

This is a car by car issue, many on this board run fine using 87 with no lose of performance or mpg. I am one of those. I have used premium and have recorded no difference at all so 87 is the call. Some on the board have had knocking using 87 and have moved to premium, this makes sense. Many on the board have just used premium with out even checking, it is their money and if it makes them happy who am I to say they are wrong.

As for the rotary by the nature of the engine's combustion chamber it will run better on low octane fuel. Many rotary race cars have been running with octane as low as 80. I have read a few posts on this board were an RX-8 ran at higher HP with 87 then premium.

The problem is that there seems to be a very inconsistent quality control with the manufacturing of the Rotary engines by Mazda. One guy runs great on 87 the next guy knocks. The only advantage that premium will give you is it will prevent knocking and may allow an advance on the engine timing. I have seen no tests, dyno sheets, or other evidence to support the fact that premium will give you more power. Maybe they is some but I have not seen them. I did see the dyno with 87 showing improved HP.

So, if your car is not knocking with 87 there is no reason to move to premium. Mazda probably recommends it as a safety net for the few cars that do knock with 87, it is cheaper for them to do this then fix the problem.

 

You cant really compare a 10:1 rotary compression to a piston 10:1 compression, they're different beast.

I cant use 87 because I use Premix, which lowers the AKI of the gas, and everytime I use 87 /w premix I got some hesitating issue.

We have 93 in NYC, so Im just gonna stick with it.

 

The resistance to detonation remains the same. The fuel doesn't know what type of engine it's in and it it still compressed to 10:1 the same as in a piston engine - granted to a different shape and flame front.

Hmmm...again I guess we all just have different engines as I also premix and use 87.

 

My Explorer knocks severely in summertime with anything less than a mid-grade fuel. It will knock with 87 if the outside temp gets into the '90's. It's beyond the ability of the computer to compensate.

Our Subaru, on the other hand, will run just fine on 85 octane no matter how hot the weather or how heavy the driver's foot is.

I agree with those who point out that a few cents at the pump is worth it just to remove this issue from the table. I always use premium in my 8.

 

What kind of mileage on the car? How has it been driven and maintained for the duration of its life?


I also use 87 and premix with no problems.

 

No need if you do this, https://www.rx8club.com/rx-8-discussion-3/no-more-detonation-%2Amiac%2A-121249/

 

My wife's V-6 Toyota has a compression ratio of 10.5:1 and needs premium.

My Accord has a compression ratio of 8.8:1 and runs on 87.

Ken

 

My 91 Toyota minivan(!) requires premium. Its compresson ratio is only 9.5:1.

 

There it is, scientific proof.


What of these vehicles/motors? Anomalies for sure.

Hyundai 2.0L 4cyl BetaII engines as found in the 03+ tiburon, accent....maybe more have a 10.3:1 compression ratio and run on 87

Hyundai 2.7L v6 Delta engines as found in 03+ Tiburon GT, 02+ Santa Fe + more have 10.3:1 compression ratio and run on 87.

Chevy 5.3 liters V-8 as found in 07+ Avalanche and others 9.9:1 compression ratio run on 87.


Again, its all about the tune.

As an example:


Honda 1.3L 4cyl as found in 2006 civic hybrid 10.8 compression ratio runs on 87

Honda 2.0L 4cyl as found in 2006 civic SI 11.0:1 compression ratio runs on 91

does2/10s a point of compression make THAT much a difference? When you take a look at how each motor is tuned, it does. But then what is really the determinant there? The compression or the tune?

 

i use shell v-power 93 octane only because it helps keeps things clean, or so they say. But I have noticed that when I use anything else, the car doesn't have the same pull. It sorta feels like it's dragging something. Could be just in my head though.

 

Yes - anomalies. Every one.

You're right - tune.

Thanks for putting all those examples up. I remember the days when it was primarily compression ratio...but it looks like memory isn't all its cracked up to be.

Ken

 

scientific proof

87 good gas.. premix.. 70k + miles...

it depends on how your drive it.. that damn ecu is smart..

beers

 

whichever works. if using regular and you don't knock then it will work.

i started with premium so i just keep using it.

like swoope said, the ecu adjusts.

 

My 88 RX-7 ran noticeably better on 87.

Both my RX-8s ran/run better on 93 w/ pre-mix.

Why? I don't know. Maybe it's all in my head.