TreknMazda

The specifications on the RX-8 website recommends PREMIUM gas. Is fuel grade going to be important with the Renesis engine?

I have driven my 1st Gen RX-7 over 256,000 miles on regular unleaded. Can hit and git as good today as when I drove it off the lot in '85. I even seem to recall an article in the old Roatary Rocket magazine about 15 years ago that recommended NOT using premium.

Since the Renesis is not turbo-charged wouldn't it do just as well on regular?

Besides, gas prices have jumped 10-15 cents/gallon here in the last week!

lefuton

i think the general consensus is that yes, you probably would be wise to choose premium (91/92 octane). this is mostly due to the fact that the renesis has something like a 10:1 compression ratio,

if that means nothing to you then look at it this way...crotch rockets are generally like 11-11.5:1 and your regular piston motor family four banger is probably in the order of 8:1

using a lower octane gas will cause knocking, and supposedly knocking is especially bad in a rotary (this i don't know why but would be most grateful if someone would care to elaborate)

-nate

wakeech

knocking is bad period, but the weakest links in the Wankel-type engine are the seals at the apices of the rotor, which are pretty darn thin, and would (usually) give out before anything else (like the rotor warping or something)....

but like i said before, knock/ping is just awful in any engine.

Quick_lude

If you can afford this car, you should be able to afford premium gas. End of story.

TreknMazda

Can you really have a knock without pistons? Seriously, I don't know. What does a rotor knock sound like?

And it is not a matter of affording premium. As I said, 17 1/2 years of driving a wankel nearly every day on regular and it is still the original engine, now with 257,000 miles on it. I've pumped 7954 gallons of regular unleaded. Premium has probably ranged from ten to twenty cents a gallon above regular over this period of time. So assume the maximum of twenty cents and the increased cost would have been $1590 or less than $100 per year. Kinda like a government tax break

Why pay for higher octane if there is no real benefit. Higher is not always better. Comression ratio on my 1st gen is listed as 9.4:1, so that's not too far off from 10:1, right?

fritts

Ignition timing is also a factor in whether or not you use Premium gas or not. Go ahead and run regular you can be amoung the elite few with Renesis rebuilds. Man I bet it will be a while before you can get parts...

KKMmaniac

The ECU would probably "dumb down" advance and other operating parameters to keep detonation at bay. Well, there goes the performance the Renesis is (or hopefully will be) famous for! I wouldn't try running regular myself though.

Quick_lude

$100 a year savings? That's chump change .. Besides most likely the ECU would retard timing and reduce power.. Looks like the Renesis will use premium gas for optimal results = hp.

wakeech

well, at least one could hope for a computer controlled (variable) ignition that could handle a lower octane if if if... i'm pretty sure that with normal daily driving (slow acceleration, low rpm operation) you wouldn't run into problems on 90 octane, even 89 octane gas, but for peak performance you'd really need to be on +91...

anyhoo, the deal with knocking is that it can be from pre-ignition combustion, or (i believe) from the fuel not burning so much as exploding all at once (not the way it's suppost to happen)... so yeah, it doesn't matter how the compression and expansion is generated, you can still have knock, rotary, piston or otherwise

Sputnik

You betcha, and how. And while apex seals aren't as "fragile" as some people make them out to be, they are the weakest link, and will be defreated with repeated and/or strong knock, which is a significant issue with forced induction.

Quote:

...Comression ratio on my 1st gen is listed as 9.4:1, so that's not too far off from 10:1, right?

It is, actually. That's the kind of difference between factory Normally Aspirated and factory Forced Induction engines in the same car.

Although lower octane gas was actually better for the FBs, this is a major redesign in the engine (and we're talking about fuel injection vs. carburetors). And if they're recommending premium, then it's probably for a reason.

BTW, nice car. Gotta love those FBs!

---jps

Beemer

89 - 90 - 91 octane????

Does that exist??? Thats SO LOW !!! Here in Belgium they only sell 95 octane and 98 octane... For me 95 octane is already low, I'll only be using 98.

amgtortoise

I know that my friend Formula Atlantic 12A Peripheral. Uses, guess what? 93 octane w/oil premix. And I've seem, most of the SCCA Rx-7 ITS cars run 93 octane w/oil premix too on their 13B's. And, a SCCA GT1 20B Peripheral uses 93 octane w/oil premix. All those mentioned race cars are Normally aspirated race engines. Also, even if they used the 13B 2nd Gen highest compression Mazda production rotors, they still use 93 octane w/oil premix. But, then they can use ATF as an octane booster too.

I assume that now that the exhaust ports on the RENESIS are no longer a peripheral port (ex. peripheral throws out all the hydrocarbons exhaust gasses, have more overlap & have a cleaner intake charge after the exhaust cycle) & being side ports to recirculate unburned hydro-carbons. Using higher octane than recommended will just cause the engine to build up more carbon deposits in a stock normally aspirated trim (all-motor).

Spending money on higher octane (>97) will just cause more hydrocarbons in the new Rx-8 RENESIS, thus affecting emissions & maybe performance will diminish in the long run.

babylou

Beemer,

There are three octane rating systems: research octane, motor octane and the average of research and motor (R+M/2). Most of the world uses research octane while the USA uses the average method.

An equivalent fuel will have a higher research octane number than a motor octane number by about 10 points. Basically 100 research octane is 95 average USA octane.

Since my head is a bit foggy at the moment I may have switched research and motor but it still does not make a difference to the point that USA fuel does not really have a lower detonation resistance. Now sulfur content is a different story.

Smoker

According to this, in terms of Fuel grades, a Rotary engine is suppose to be able to use a lower grade of fuel without any issues.

Take a look at this article in the Fuel Efficiency Section [EDIT] and let me know what you think.


The Renesis Rotary Motor

Smoker

Well, So can we just use our pain old regular unlead fuel for this engine or what ?

zoom44

sorry for this rater cheesy answer- use the fuel grade recommended in the owner's manual. and since we haven't seen one yet no one can say(unless they get some info from mazda) what that recomendation is.

fritts

Post the section on Fuel Consumption. All I see is a fuel efficiency section and it only talks about running on a leaner mixture not a low octane mixture. Both the press pack and Mazda website say premium. So I would assume that premium is what your supposed to use. You can be the first to try the low octane stuff if you want I don't care.....

llama

Would Chevron with Techron keep a rotary engine cleaner also?

neit_jnf

A leaner mixture is more prone to detonation/knocking than a richer mixture. This may be the reason for the Renesis to use premium

RacerX7FB

Driving the car and hitting redline a couple times a day will keep a rotary engine clean

VWjet

So what I'm hearing is that leaner fuel can be used, but this is not officially from Mazda. Then again, are we going to adhere to everything they tell us???

wakeech

leaner doesn't mean lower octane, leaner means a higher ratio of air to fuel (or conversly a lower ratio of fuel to air)... the average buyer has nothign to do with the fuel:air ratio, the ECU determines that.

because of the higher compression ratio (10:1 i think), it's very adviseable to use only Premium gasoline, especially if you're planning on revving it (which one ought to, if they buy the car).

8_wannabe

Folks, I got my car and I got my owners manual. And here's what is says about Fuel, page 4-2:

"Your Mazda will perform best with Premium Unleaed Fuel, Octane Rating 91 [(R+M)/2 method] or above (96 ROM or above).

You may use a regular unleaded fuel with Octane Rating from 87 to 90 (91-95 ROM) but this will slightly reduce performance. Fuel with a rating lower than 87 octane (91 RON) could cause the emission control system to lose effectiveness. It could also cause engine knocking and serious engine damage."

They also say use nothing with more than 10% ethanol or any fuel system additives or cleaning agents not specified by Mazda.

I will use a maximum of 89 octane, and I'll probably use 87 octane on occasion. Knowing how these books are written, they are being most cautious and recommend premium to give you the optimum driving experience. Slightly degraded performance of an 8 far exceeds anything I have ever driven so I'll still be happy. With MPG shaping up to be as poor as it appears, I'll offset with 89/87 which according to their manual will still be ok.

vudoodoodoo

Put what the manual suggests. Premium.

8_wannabe

I will do what the manual suggests, to wit: "You may use a regular unleaded fuel with Octane Rating from 87 to 90 (91-95 ROM)." That is exactly what I will do.