Red Devil

Initially, when I backed off of 93 to move to 87 octane I did to it during the Chicago winter. I figured the 20 degree temps would help avoid detonation a little better, just in case. As it got warmer with the spring, I contemplated switching back, but decided to leave it as was and haven't looked back since. That's the most I can offer from personal experience.

Raptor75

The Octane rating dose not effect your plugs it can cause pining which will punch a hole in your rotor face or other structure damage.

If you car is not pinging your throwing money away with Premium fuel.

Chasvhill

I remember a quote from an article I read once about fuel octane rating. Paraphrased, it said - using extra octane in your car is like taking extra vitamins for your body. And we all know what the body does with extra vitamins.

Good analogy.

Silver_Surfer

Good Point! (just had to use this )

staticlag

After seeing my dyno with 87 octane and 10w40 dino oil, I think i'll "stay the course"

ken-x8

In one of these octane threads somebody posted a link to a test that a car mag did on octane. The basic result of the test was that their test cars did not ping when run on low octane (they shouldn't ping - the ECU and knock sensors adjust the timing) but there was measurable power loss.

I don't remember the details like which cars they tested, or the percentages, but it should be possible to search for the post and article.

FWIW, I think I take more vitamins than I really need. Hard to know exactly what my personal needs are. There's probably excess that goes to waste, but at least I'm not short on any essentials.

Ken

BunnyGirl

Most vitamins you can only absorp up to a certain amount so the rest just goes to waste (literally) anyway. LOL

Anyway, I remember the article you are talking about, which is one of my reasons for sticking with premium also.

BlueRenesis82

BunnyGirl
This message is hidden because BunnyGirl is on your ignore list.

Renesis_8

The rotary engine is different from piston engine, dont compare or relate other tests conducted on piston engine.

Its just how the rotary engine behaves, it wont gain a lot of power like pistons even with race gas with the most aggressive tune. Another thing that is unique to the rotary is that it wont give more power with higher compression ratio, like race pistons engines. They are different, as simple as that.

Also, turbocharged rotaries are different as well... dont put 87 in that =d

Back on the topic, just use whatever grade of gas you feel comfortable with. If you think its safer for your car, then its not a waste.
________
LIVE SEX WEBSHOWS

Raptor75

Very well put.

Paul_in_DC

I tried 89, and got a slight rattling sound. With 93, no rattling. Now it's 93 all the way. The car's happy. I'm happy.

HCTR154

I've used 87 octane since I bought the car back in February. No "marbles in a coffee can" for me. Also, I try to use Exxon or Valero gas. Around here they are priced very competitively and therefore always have fresh gas being put in the in-ground tanks.

Back when I lived in Beaumont, Texas (just a few feet above sea level) I noticed a lot of standing water in parking lots of certain gas stations after heavy rains. Try to avoid those for obvious reasons.

ken-x8

I understand that there are significant differences between a rotary and piston engine: the whole rotor vs piston geometry. But it's still Otto cycle, and there are thermodynamic basics that aren't going to go away. Also basics of engine timing, octane, etc.

All of the reports of these engines running well on 87 are pretty comforting, though. I've never heard anything nearly as good about running piston engines on lower octane. I now feel really wasteful about using 93 - all of the gas stations I encounter have 87, 89 and 93. Maybe I should start filling 50/50 with 89 and 93.

Ken

kartweb

Some of us have. I buy Phillips racing fuel by the barrel to use in some motors that simply won't run work on pump fuel alone. Mazda obviously tuned these motors to the best limits a production motor could give, in fact they keep doing little tweaks - see if Honda or Nissan will do that.

It's not so much the octane that makes it better it's the oxygenation and the higer cooling effect. When I mentioned that over on the mods board the know-it-alls who never tried it went nuts. I suppose if I spent another $5000 to add another 50 HP at the expense of making the car's drivability and reliability suck, I'd probably be bitter when someone mentioned how some fuels can boost power too. But it's not the octane that does it.

Fanman

Again it's not an on/off switch. Understand that. The engine adjusts timing based on several factors. If you put 87 octane gas in, the car is adjusting the timing for that grade of gasoline. It's pulling timing. Can it run on 87 octane...yes. Is it running at it's optimum timing (max hp)...no. Again, look at it as a range of 1-10, not an on/off switch. If 87 is a 1 (the minimum grade of gas the car can run on, and a few people have gotten lower octane/bad gas and gotten detonation), then 93 octane is a 10 (at that point the car has advanced tiing as far as it can). So the question of why not just put 100 octane is at that point, it is useless as it has advanced the timing as far as it will go. On the opposite end if you put in 85 octane the ECU cannot retard the timing enough so you get pinging.

The example of vitamins is disengenious. It's more like you have a track & field athlete that should get say 1000 mg of a particular vitamin, but you give him 600 mg that is good enough for most ordinary people walking around. While he can function on that 600 mg, he functions better on the 1000 mg a day.

Raptor75

There is one very important point you have omitted. The rotary engines combustion chamber inherently is more efficient running lower octane. With the longer narrower combustion chamber the quicker burning (not exactly what happens) lower octane fuel is advantageous. I have read of rotary race engines running 80 octane because of this property. With the RX the slight lose you experience with the lower octane as you pointed out is more then made up for with the increased efficiency. One of the turner shops here was working with modded mapping found he could get more horse power with 87 then 93.

If your engine pings with the lower octane you have a very good reason to use the higher octane. If not, your are throwing money out the exhaust. It's your money and if it makes you feel better or safer go for it but the fact is your not going to see any performance increase with this and are just as likely to see a decrease. My own mileage dropped .5mpg with 93 oct.

MazdaManiac

iTrader: (3)

Not really, no.
The engine has no way of knowing what the octane rating is of the gas it is burning. It just starts the combustion process and lets the cards fall where they may.
If there is pinging, it is supposed to pull a lot of timing at that moment and record a weighted average of the timing at that load point.
Over time, it will accumulate a timing profile much in the same way that it builds LTFT.
However, in practice, the Renesis knock sensor sucks as it is tuned for a range of frequencies and it hears none of them well.
If you run at the edge of detonation, you will simply get a terrible timing curve.

Beodude123

Look, the ECU can't distinguish between octanes. The car doesn't know what kind of gas you put in it. The car will run the most timing advance that the car is programmed for, regardless of octane. Now if the engine knocks, then the knock sensor will detect that, and send a signal to retard the timing.

Also, the only time you are really going to be running rull timing advance is when the engine is cool. Once it's warmed up, it will probably be cutting timing back by 2-4 degrees.

Fanman

So, aren't you basically telling us the same thing ? I'm not saying that an engine/ECU can detect a grade of gasoline, but rather it's different combustion properties. i.e. if a particular grade of gasoline burns hotter, detects detonation it pulls timing immediately. It's not as if you drive and have to hear seconds, or minutes of pinging. The ECU calibration is already pulling the timing based on the pinging, and other factors it detects long before the human ear might be detecting it (at that moment). Your getting a terrible timing curve, the engine is pulling timing, i.e you are losing hp.

Beodude123

Ooops. I guess I should have read the post above me... LoL


Higher octane gases burn slower, which is why they prevent detonation. Technically, if you can run the same gas, with the same ignition advance, you will have higher power (maybe a fraction of a hp). Mazda probably recomends higher octanes because it extends CAT life (more unburned gas)... LoL I don't know. It's kinda like how they say not to use synthetic. All because one brand of synthetic (Was it Mobil 1?) didn't work well in the rotary.

Fanman

Take a look at this article. I'm not one to say that our engine is superior to say an M3's (yet still a bit different). In this case, no pinging was detected yet timing was pulled & performance was degraded. Again, I'm not saying you can't run 87. You can but you are on the very edge of what this engine can handle (people that have run lower octane have gotten really bad breakup).

http://www.caranddriver.com/features...r-premium.html

Fanman

The factory has set their optimum timing curves/calibrations at 91. Why wouldn't they at 87, if it indeed ran better gave more mileage and better hp ? Imagine this. You are Mazda, you can either sell the RX8 claiming 232 hp with 91 octane, or magically if you run 87 you get say 240 hp. Not to mention you get better EPA gas mileage statements on your stickers at the dealer. Why wouldn't they do it ? 87 is readily available across the country. 91 is the best commercially available gasoline in many parts of the country, so that is why they set their optimal timing/calibration at 91. Could they set a more aggressive one 100 octane, or 103. probably, but then most people can't get it, or are not willing to spend $5/gallon for a few more hp gain. The "10" in the range is set at 91, maybe 93. that is why above that you won't see any greater effects. But if 87 is the cure to the common cold, then why don't they make it the standard/recommendation ? They can tout a stronger engine (more hp), and better gas mileage.

silverx8

No discussion of gas grade is complete without a discussion of "boutique" gas. There are dozens of gas formulations depending on where you live brought on by the EPA (local and Federal). The additives that affect the octane vary by region and county.


Some 87 octane somewhere is bound to work better than 91 somewhere else in the same car, and vice versa. You could be buying MTBE laced gas in one place and Ethanol laced gas in another. Both would perform differently in the same car. The last thing on the politicians minds was how this "boutique" gas affects rotaries differently.

http://www.eia.doe.gov/oiaf/servicer.../gasoline.html

Explains some of the issue related to price, but says nothing about performance.

AdRoCK3217

I stopped reading after the first page. I'm just going to sum up (with no long explanations) as to WHY the RX8 should use 91octane and above.

1: US "gasoline" is now up to a 10% mixture of ethanol. Your 87 is NOT 87 anymore. Think of 89 as the new 87. And 91 as the new 89, 93 at the new 91...etc..

2: The RX8 has a 10.0:1 compression ratio. This is the FIRST and ONLY naturally aspirated NA rotary that will actually make MORE power on octane ratings of HIGHER than 85/87. The FB's and FC's (non-turbo) make peak power on 85. The RX8, with its 10.0:1 compression, our ethanol-injected gasoline, will have peak power on 91+ octane.

MazdaManiac

iTrader: (3)

^^ Ah. Maybe you should have kept reading before you imparted your unbounded wisdom.