Hi all,

I did a quick search, but came up with nothing recent. All rotary history talks about better performance on lower octane fuel. Even the US threads on this site confirm that.

What I am wondering is if the PCM cals in the Aussy models really require 95RON fuel? The big sticker on the fuel cap is tending to sway me from giving ULP a go.

I nearly always used 98RON in my LS1. I am not convinced the '8 needs it. So I thought I would like some input from y'all.

Maybe some runs on a chassis dyno will let us know for sure. When we get some numbers up, and have a few miles on our cars, I can organise a Dyno day (morning ;) ) at PowerTorque.

Cheers,
Hymee.

I'm no Expert on Rotary or even ever own a rotary engined car. But i think Using the 98 RON Fuel should keep the Car running in the best condition but of course depend on which Fuel Company. I heard lot's of people highly recommend to use BP Ultimate or Shell Optimax over Mobil Synergy 8000 or Caltex Vortex. But i'm not sure if any one can confirm this?

I normally use Mobil Synergy or BP Ultimate instead of Shell Optimax. I realise the other two has better performance and better fuel economy than the Optimax.

Winning could you PLEASE EXPLAIN your thoughts on why shell optimax , is not as good as mobil or bp , dont get me wrong i am not loyal to any particular brand just curious???

BP Ultimate was definatley the preferred fuel amongst the LS1 guys. We don't get Mobil Synergy here in QLD yet, just the Mobil 95 RON PULP. We avoided Craptimax, but I don't really know why. I guess it is religious wars really.

But lets get back to the topic - Can we really use lower octane in the rotaries? Some of the cleanliness issues are moot when it comes to rotary engines:

[list=1]
There are no blow-by gasses in a RC engine - so oil contamination is not really a worry.
There are no valve components to foul/carbon up, require lubrication.
The afterburner cleans up most of the unburnt combustion gasses.
[/list=1]

About the only benefit is potential cleaner injectors, but does "modern" ULP provide a cleaning benifit anyway?

Cheers,
Hymee.

My 2 cents..

Been primarily running Optimax since it came to Canberra (3 odd years ago), mostly because it's the only one that every Shell servo stocks, there's only 2 BPs in Canberra with Ultimate.

Optimax was okay but every third or fourth tank seemed to be dodgy (poor milage, felt less zippy to drive with)... of course, nothing I could do to prove any of it, but it certainly felt that way and my L/100km figures always reflected the feeling..

Ultimate 98 seems more consistant with it's quality. Also, it's only 6 cents more a litre here, as opposed to Optimax which is about 9 cents more.

Either way, got roughly 10-15% more kms per tank with them compared to normal unleaded.

I also have little faith in regular ULP because of all the sulfur, etc etc whereas the premium fuels are a bit more pure (from what I know anyway)

No idea which way would be better for my 8 though, so until then, I'll run Ultimate.

Originally posted by Lock & Load
Winning could you PLEASE EXPLAIN your thoughts on why shell optimax , is not as good as mobil or bp , dont get me wrong i am not loyal to any particular brand just curious???

With Optimax:

1. Less mileage, at least 50 kms less every full tank compare to Mobil Synergy and BP Ultimate.
2. Not as zippy?, meaty?, responsive?, punchy? when I press the throttle. I don't know the right word for it!:p Throttle just not as solid as Mobil or BP, with Optimax it feels very hollow when you press the pedal.

My opinion is based on my driving style and also based on my previous cars , CLK430 V8, WRX Sti 4cyl-turbo, Eunos 30X V6, Honda Civic 4cyl. My RX8 only done 400kms, so honestly I don't know whether it applies on RE. My first full tank done 320kms before the fuel light on. Mostly city driving and never rev it over 7000rpm. Well, honestly I did rev it to 9,500rpm once, only once, can't resist the temptation.

Winning and others thanks for your input , i will definetely try BP ultimate in my next fill and see if i can notice any difference.

That may explain my sudden poor fuel economy. Up to my service, I had been using Mobil Synergy 8000, but my last two tank fulls were filled with Shell Optimax (Coles 4 cents deal).

I was getting 16.5L/100km. Today it improved to about 15.5L/100km. That was because I was driving with the proverbial egg between my foot and the accelerator pedal. Datsun 120Y's were out accelerating me at the lights.

I think I'll refill with Mobil and see how it goes.

Donald

So far I have collected the following stats, in chronological order:

1st fill Mobil PULP 95RON 13.2 L/100km
2nd fill Caltex Vortex PULP 12.0 L/100km
3rd fill 711 PULP 12.8 L/100km
4th fill BP Ultimate only just filled ;)

Totals up until 4th fill: 1358km, 170.95L = 12.59 L/100km

Really, it is too early to tell. If the US guys reckon not to dyno them untill 4000 miles, then I have a fair ways to go.

Cheers,
Hymee.

Originally posted by donaldc
That may explain my sudden poor fuel economy. Up to my service, I had been using Mobil Synergy 8000, but my last two tank fulls were filled with Shell Optimax (Coles 4 cents deal).

I was getting 16.5L/100km. Today it improved to about 15.5L/100km. That was because I was driving with the proverbial egg between my foot and the accelerator pedal. Datsun 120Y's were out accelerating me at the lights.

I think I'll refill with Mobil and see how it goes.

Donald

What were you getting on Synergy?

Your experience seems to add substance to the Craptimax moniker.

Cheers,
Hymee.

Around 13.5-14L/100km for Mobil Synergy.

Donald

Originally posted by Winning
I normally use Mobil Synergy or BP Ultimate instead of Shell Optimax. I realise the other two has better performance and better fuel economy than the Optimax.

I feel this way as well!

I had always been a loyal customer to Shell, used to drive a fully AC Schnitzer moded E36 M3 and through out the ownership of that car, only shell went in... until I changed to 350z.... well.. not immediately... but after having shell in for 4 months in the Z, I decided to change my fuel to Mobile 1 synergy 8K as my people (including dealers) recommand that fuel... now I feel the engine runs MUCH MUCH smoother and the idle isn't as rough as before... but I am not too sure about the fuel economy as I don't really pay attention to that.... it is a performance car, same as rx8, therefore, shouldn't really care about this IMO... enjoy your 9K rpm guys! (sadly Z only has 6.6k rpm to play with...). And performance wise.... well.... cannot really feel much different, but when the engine is smoother, you will get a bit happier to hear it revs!

cheers,

richie

After reading this topic from you guys,really makes me rethink what I should use.I been using Optimax for a longtime with my cars,since the station is really nearby.But if there is more benefit to use others, then I wouldn't mind to go out further just to fill up.Going to try it out to see.Thx for all these infos guys.

BP Ultimate would have the be the best fuel i ever used.

For some reason it just preformed better than synergy and optimax.

S6 RX-7.

I also ride a bike... (High rev engine) and it never recommend Optimax, it produce soo much ping from the engine is not funny.

I presume the Rotary engine is work in similar manner, so I was tried all sorts of fuel except Optimax.

I get about 350KM before the low fuel light comes up. My first service is tomorrow.

I'm quite different....Getting about 500km for a tank of optimax. Mileage about 2700kms. Do rev sometimes...But I will try BP for my next refill.

I just got my welcome pack last night, and I noted that in the little pamphlet they made particular reference to using 95 octane fule and 5-30 grade oil. I don't want to void my warranty by going outside recommendations.

Originally posted by labrat
I just got my welcome pack last night, and I noted that in the little pamphlet they made particular reference to using 95 octane fule and 5-30 grade oil. I don't want to void my warranty by going outside recommendations.

Yes, the warranty is important. A higher octane fuel, such as 98 can't possible void your warranty. But the reason you stated is what is stopping me from trying normal 91 RON ULP. It is only because of all the mention of 91 RON giving better results in the US I asked the question. Rotaries are documented as not being so sensitive to lower octane fuels. I wonder if the ECU's in our AUS '8s here have a different spark table than the US due to different fuels etc?

The octane number is the anti-knock rating, not a power related figure. But higher octane fuels are required for higher compression engines, and higher compression gives more power - hence the apparent link between Octane and Power. Many modern cars that are designed to run on ULP will produce more power on PULP because the ECU finds it can put more timing in (more spark advance). This is because of the knock sensors, and the ECU's ability to 'learn'. Conversely engines requiring PULP will run OK on ULP as the ECU detects the onset of knock, and takes timing out.

Cheers,
Hymee.

Octane levels are rated differently in US. and UK to that of AUSTRALIA i will stick to 95 or higher octane levels .

Yeah - good point. RON, MON, PON...

http://www.medfordfuel.com/octane.htm
http://www.refiningonline.com/EngelhardKB/crep/TCR4_29.htm
http://www.motorcycle.com/mo/mcnuts/fuelron.html

Cheers,
Hymee.

Hymee,

I feel your pain, and I still don't think we have gotten to the bottom of this question. I have been doing my own reading throughout the forum and there seems to be a good argument from guys in the states to use 87octane (91RON) fuel in our Rx-8 instead of 95RON (PULP).

This has been a BIG discussion point in other parts of the forum. In summary, the concensus seems to be that 91RON (regular ULP) fuel burns more completely, and as a result the engine idles & runs smoother and produces less 'soot' out of the exhausts. I know that our manual recommends 95 RON (PULP), but it doesn't forbid less.

If I get the balls to give regular ULP a go, I'll let you all know my thoughts. Anyone else curious?

DGW , yeah i am curios but my car is running very smooth on 98 octane , so why rock the boat , the bit of soot on the rear is not a major concern , the cooling effect of a higher octane level on a rotary engine may be the reason mazda has recomended 98 octane??as opposed to 91 .
However if you try 91 i will be interested in your findings.

Slightly off topic perhaps, but I just filled up (with PULP) after a mix of suburban and highway driving, and recorded 10.2L/100km (23.0miles per US gallon for the seppos). Not as good as my old Celica where I regularly recorded under 8L/100km under similar driving but what the hell. I think it takes a while to adjust your driving style to the RX-8. The driving instructor guy at the Brisbane driving day said that he tried to drive so that the motion of the car was totally seamless without jerking or surging, and that is what I'm looking for.

The driving instructor guy at the Brisbane driving day said that he tried to drive so that the motion of the car was totally seamless without jerking or surging, and that is what I'm looking for.

Hey labrat,

I don't know about the jerking, but the surging is exactly what I got the car for... :D

Over a month and covering a couple thousand km, a heavy foot (say 15 l/100km compared to 10l/100km) would make a difference of $20~25 per week.

...about half a bus fare!

For me? It's zoom-zoom!!!

I'm probably happy compromising slightly higher consumption for the low center of gravity and ideal weight distribution that gives these cars the great handling that they have.

Not to mention I can short shift at 7000RPM :eek: and still go like the clappers. (ROFL)

Cheers,
Hymee.

Hi All,

Basically RON numbers are for a lower rpm/load and Optimax, Synergy and Ultimate are all 98 RON and so should have the same response at lower rpms. The difference is in the MON which is for higher rpms/load. Here Optimax 98RON has the same MON as its regular 95RON petrol, but Ultimate and Synergy have a higher MON, and therefore the extra response for higher rpm speeds. This is why people feel that Ultimate and Synergy are quicker than Optimax as the rotary is such a high revving engine, and also is why motorbikes generally dont recommend Optimax. However, Optimax also has extra detergents that clean your engine and hence it is good for every third or fourth tank. Also, some batches of Optimax tend to have more sulfur content than others, depending on demand.

Hope all the talk of RON and MON isnt too confusing.

I know this thread is getting old, but I've been doing some experimenting:

I tried 1/2 a tank of 91 RON ULP 2 weeks ago, then 2 tanks of BP Ultimate and now I am on a full tank of 91RON ULP again. Initial findings:

IDLE: The car seems to idle lower with ULP (800rpm) than it does with PULP (1000rpm). No noticable difference in it being a 'smoother' idle with one or the other.

NOISE: I've done 5000km now and I have to say that the exhaust note sounds louder running on ULP. Does this mean more power? I don't know.

EXHAUST: Not sure yet if there is less soot on the pipes.

PERFORMANCE: No noticable difference power between the two fuels.

ENGINE: The engine purrs beautifully with either fuel. No knocking, pinging or funny noises running on ULP.

Conclusion? The jury is still out.

Hmm... mine idles at 800 with BP Ultimate

Mine sits smack on 1000rpm while running on BP ultimate. Has 1230km on the clock.

I notice a difference (I think) going from BP premium to ultimate. I'll experiment a little no that I've got fresh oil :D

Originally posted by sco
Hmm... mine idles at 800 with BP Ultimate

Bzzzzz ;) Mine idles at 800 im pretty sure. I haven't noticed any difference between fuels, but I have mainly been using BP Ultimate.

Thanks for having the guts to try 91 DGW. You da man!:cool:

Cheers,
Hymee.

PS - Nearly 4000 km on the clock.

I gave Madza a call today regarding this issue. I was told by the guy on the phone that the ECU is designed to run on 95 RON, so that's what you should use. I asked him about lower octane and mentioned the discussions in the Forum, to which he had no comment other than to say that he was telling me what was told to them my Mazda Japan.

I haven't seen enough difference between the two fuels to warrant sticking to 91RON against Mazda's recommendations. Hence once this tank is gone, I'll probably go back to PULP.

That being said, I haven't had any bad experiences on regular unleaded and indeed the engine ran just as smooth and fast as ever, so if you ever find yourself in the middle of nowhere with no access to PULP, don't fret. IMO the RX-8 takes 91RON fuel in it's stride without a problem.