Jeb

So what's best octane on a na s4?

TheAbsence

iTrader: (19)

^ 87

SR20detFC3S

iTrader: (1)

from what I've heard for na you should run the lowest octane you can get

Evil Aviator

AVGAS is chock full of lead, and will damage some parts of an EFI vehicle. ("Low lead" is a relative term). Also, AVGAS will not burn properly unless the car is tuned for it. I believe the current fine for using AVGAS on US highways is $10,000 per offense, so I would not recommend it for street cars.

Octane is strictly an anti-knock rating, nothing more. The S4 and S5 turbo and non-turbo cars are rated for a minimum octane of 87 using the R+M/2 method, and you will find this information in the owner's manual if it is still in the car. Higher octane will work just fine, although it costs more money and will offer no benefit unless your engine would knock with the lower octane fuel. There is no "best" octane for an NA S4 because it will not knock with any type of modern pump gas unless the engine is in very poor shape. As mentioned earlier in this thread, just stick with Top Tier gas if you want clean burning.

Yes, on these forums you may hear that the lowest octane possible will make the most power. This is from a misinterpretation of a racing book in which it was stated that a lower octane race fuel produced better results than the higher octane fuel. This was due to a higher energy content that the lower octane race fuel just happened to have. Some people took this to mean that all low octane fuel has a high energy content, which is not true. It would be like saying that red cars are the fastest because the car that won the race was painted red.

TerrorismSux

Dude in a 7? I agree with the "hardcore" statement before and after the recommendation. not to say that it cannot be done, nor to say it will kill your car. Just, dude... its the holiday season. Put some good ol 87 in her and spend the extra cash on another quart of oil

(no disrespect intended, just contributing for fun )

TerrorismSux

Just in case my previous post is misinterpreted, use ONLY 87 Octane gas in your RX7.

If you would like to ask why, I can tell you what I was told by my car club. The Octane rating in the fuel doesn't make the fuel "superman" it is only a "type" of fuel for a certain "type of cars". The Octane actually slows the combustion cycle, or rather "extends" it, causing it to burn hotter. In a piston engine it will run only a little hotter, due to the cycles that take place, allowing time before the next compression, but with rotary you may end up finishing your combustion when you're already at your exhaust cycle, causing MAJOR damage to your exhaust manifold and the gasket connected to your exhaust.

Also MazdaTrix informed me that the RX7 runs hot on exhaust as it is, and that the best fuel to use was the lowest octane to ensure maximum explosion during optimal cycle. I'm still new to rotary engines, but thought I'd let you know what I found out today

TL;DR = 87 octane best. 85 if you're in ND. Do not use Leaded.

chromerunner

been useing 93 in my 7's..after reading this ill try 87..thanks

mar3

iTrader: (8)

..after reading this ill try 87..thanks

It's just a matter of cost. If you can afford 93 octane, you're more than likely also getting a better additive package from the alchemists who mix the gas flavors for the tankers delivering the fuel to the gas stations. It's just not necessary.


Where does one begin. First things first....gas does not explode in any engine. You need to wonder about the person telling you this no matter what company they work for.

Octane is merely the measurement of a gasoline's ability to resist pre-ignition, nothing more. The actual characteristics of gasoline burn, volatility, etc, can vary completely independent across different retail sellers at the pump despite having the same octane rating. Making generalizations about gasoline behavior by saying crazy stuff like you were told helps no one. Keep the message simple is just better.

The rotary runs hotter at the exhaust side because there is no "down cycle." In each part of the housing, the intake is ALWAYS sucking in air/fuel, ALWAYS compressing, ALWAYS burning and then ALWAYS expelling exhaust fumes. It's why these engines eat up spark plugs, cheap carbon graphite spark plug wires and gas. Each section of the housing is ALWAYS doing its duty with each face of the rotor as it sees the rotor face spin by, thus the exhaust port is ALWAYS getting spent exhaust unlike in a piston engine where one up and down stroke of the piston will not have heat or exhaust gas heat involved. The exhaust ports of the rotary engine are hotter than "normal" as a result.

To recap...on the stock, naturally-aspirated rotary engine, you can run any octane gasoline you want, from 85 on up, it's just that there's no point in it unless the higher octane grades of gasoline have better additive packages, which they often do.

gerald m

I think I will just add a little ATF. fluid that should do the trick.. You guys will have to come to Canada and get some good stuff buy the time it goes down that big long old pipe line to you guys half the zip is gone already There that should get some action for you Mario I can just tell you love this thread ...

Johnny Herbert

Dear Friends:
We are having a problem here, in my country, (Argentina): we have only 3 types of gasoline:
98 octane.
95 octane, ( but with 15 % of alcohol, I suposse methanol).
91 Octane ( but with 30 % of alcohol, I suposse methanol).

If I am understanding well, ( sorry, I´m not native in english, and could have some problems with the language), the less octane is better.
With these idea in mind, I must put the 91.... but....
What´happenned with the alcohol? Because I understand that some parts of the fuel line could be damage if it´s not the appropriate material, that resist the alcohol.
Probably is a vey specific question, but thank you if somebody knows the answer.

Evil Aviator

That is not exactly true. The octane rating is simply an index for the anti-knock properties of fuel. In the USA, it is an average of the RON (ASTM D 2699) and MON (ASTM D 2700), which you can order from the ASTM website if you want all of the details. It has little to do with the actual amount of iso-octane in the fuel, which could be zero. The octane rating is not necessarily related to the heat of combustion nor the flame speed. It is simply an anti-knock rating, and nothing more.

The octane rating does not necessarily have any relationship to the burning speed. Also, the air-fuel mixture is not supposed to explode, so you would certainly not want to achieve a maximum explosion unless you are trying to blow up your engine.

Contrary to the advertising that is trying to mislead consumers to buy the high octane fuel with the higher profit margin, nearly every brand of pump gas uses exactly the same additive package in all their octane grades. The only difference is that a few brands use a slightly higher percentage in their premium octane grade.

You would have a good laugh if you actually saw the guys who you are calling "alchemists", lol.

+1

I'm not sure why some people try to pretend they are a witch doctor and can read the bones of a yellow octane rating label and then automatically know all of the other properties of the fuel.

The alcohol in your fuel is ethanol.

Yes, some of the parts of your fuel system could be damaged by alcohol levels above the maximum recommended 10%, but I do not know specifically which parts because I have never tried it in these cars. Normally it mostly affects fuel gauge senders, fuel pumps, rubber fuel hoses, gaskets, and aluminum parts. Ethanol fuel conducts electricity.

mar3

iTrader: (8)

I saw the 91 octane with 30% ethanol and I was screaming, RUN AWAY!!...the stuff attracts water like crazy. You want less ethanol, not more. For Herbert's case, I'd say fill up with the 95 octane and replace all the rubber in your fuel system, back to front, just to play it safe. I've seen articles stating there could be engine damage for older engines and also articles saying there's no risk at all and neither citing studies that have been duplicated yet.

No one knows what dangers this new gas concoctions with ethanol represents to older engines right now. They're just guessing. The rubber thing is true though, I feel, and it's because all of my lines, including replaced ones that weren't even two years old at the time, are needing to be replaced and we've had the 10% stuff for roughly 5 years now. That's just too short of a lifetime for fuel line.

Johnny Herbert

Dear Friends:
I am very grateful with your dedication, intersting observations, and opinions.
I agree also with the pre-opinant who said that could be impossible to evaluate how deep could be the damages produced for the use of Ethanol in fuel.
Particulary I´m not considering that alcohol is very hygroscopic, and all these molecules of water can produce galvanic corrosion. This was an excellent point. Especifically in aluminium engines.
I will continue using the no alcohol gasoline.
Yours faithfully.
J.H.

foo411

I am a Newbie so bear with me.. Higher octane fuel has the ability to withstand higher pressures and temperature with out pre-igniton, it also burns at a slower rate.. AvGas 100LL is 100 octane rating but contains some tetra-ethyl lead to increase spontaneous combustion even further.. Leaded fuels are used in performance vehicles (Race cars, Planes etc..) Running avgas is possible but not practical due to the lead build up and lead fouling.. Take the bottom plug out of a recip plane and youll see what i mean (sounds like sand coming out)!

Evil Aviator

High octane fuel does not necessarily burn at a slower rate. That is just an urban legend. Fuel with a higher octane rating may burn faster or slower than a fuel with a lower octane rating.

http://www.rockettbrand.com/techsupp...ationships.pdf

http://www.stockcarracing.com/techar...urn_rates.html

the pope

the sea foam acts as a lube and conditioning additive. its good stuff but in moderation. some cars have been cleaned too well and the carbon holding together the engine disapeared but it unleashes multiple cans of worms. its good in the fuel systen because of its lube capabilities. helps out injecters and stuff! i have used it before and its great stuff!

mar3

iTrader: (8)

Good freakin' grief....let's get this perfectly clear...octane number has nothing to do with what the gasoline characteristics are beyond this one simple behavior:

Where does the gasoline sample lose control and pre-ignite in more than one spot in a test chamber? OK...that's 87 octane gas. Or 93 octane gas. Or 118 octane gas.

That's it. That's all. You cannot ascribe any other characteristics to a particular blend of gasoline based simply on the octane number, so please stop already.




ps. Use Shell 87 octane.

djphonics

iTrader: (1)

This is what I use now. I noticed quite a difference from dropping from 91 to 87. She got even more fun. I'm in a na s4 as well.

EDIT:
Octane relates to the octane level in the gasoline, obviously. This is the real burning chemical in our fuel, and higher octane levels are slower burning. That's from my shop teach, and corresponding text book. (i'm too lazy to go grab the book right now, but i could snap a pic for everyone to look at another time.)

Evil Aviator

There is usually very little difference in energy content between the different octane grades of pump gas from the same gas station in North America. For example, Chevron UTG-96 (92 Octane) has an energy content of 18,400 BTU/lb and specific gravity of 0.740, while Chevron UTG-91 (87 Octane) has an energy content of 18,500 BTU/lb and specific gravity of 0.735. Working the math, UTG-96 has about 1/2% less energy but it is about 1/2% more dense, so it has about the same energy content per volume as UTG-92. Therefore, during acceleration there would be no difference between the fuels because the computer injects fuel by volume under this condition.

If you noticed a difference then it is either just in your mind, or you changed gas stations. Different gas stations do have different gas. For example, my cars and my truck run well on Shell and BP 87 octane, but Texico 87 octane runs a little rough at idle and doesn't seem to have quite the power that it should. Ethanol content probably makes the most difference, but there are also many other factors.

Oh good God.

The octane rating does NOT necessarily relate to the actual iso-octane in the fuel. Some fuels have zero iso-octane, yet have an octane rating. The rating is relative to the anti-knock properties of the fuel as opposed to a percentage of actual iso-octane in the fuel.

Fuel rated at a higher octane does NOT necessarily burn slower. The main reason is that different companies and different regions will use a different mix of components in a given fuel. High octane aviation fuel does tend to burn slower, while high octane automotive race fuel tends to burn faster. It all depends on how the company formulates the fuel, so you can't simply go by the octane rating.

mar3

iTrader: (8)

Unless this is a Junior tech college, there's a reason he's your shop teacher and not your chemistry teacher and it just showed. You've got it backwards because octane level describes NOTHING but the ability of a sample of gasoline to resist pre-ignition.

THAT IS ALL THE OCTANE NUMBER IS ABOUT, PERIOD!

You cannot use octane numbers to make any other generalizations about that sample of gasoline or the gasoline at the pump that has been given that octane number because the characteristics are not linearly related to each other at all. Octane number is nothing more than one more way to define a gasoline's characteristics.

It's like saying, "You want to use pink gasoline because that's the best gasoline for high compression engines, it has a high octane number, " and it's sitting in a drum, completely unmarked. All you can see is that it's pink.

Do you see the point now?

I'm begging everyone to stop posting misleading info or info that's decades old and simply wrong. Stick to the topic of this thread which was actually done many posts ago.

Regarding the butt dyno, I tend to agree with Evil Aviator. I experienced the same thing but it was when I ran a tank of Shell when the car normally only gets Kroger (yes, the grocery store chain... ). This could've been due to the different additive package or it could've been due to a different blend sold to Shell that Kroger's won't pay for. I have no way of knowing since both tanks were 87 octane.

Evil Aviator

I guess I should point out that I have several years of experience with international fuel contracts, as well as some experience running international aviation refueling operations and a MOGAS/AVGAS fuel farm. I also have a lot of experience in engine performance analysis. You noobs probably didn't realize this since you never know what kind of nut is behind the keyboard on internet forums, and I suppose misspelling Texaco in my last post didn't help, lol. I am not a chemical engineer, so there is a limit to my knowledge on this subject, but I am pretty confident about what I have posted.

Most college and tech school programs are oriented toward maintenance. Therefore, all they usually teach about the octane number is to use the recommended fuel specified by the manufacturer, and they may include a short and confusing definition of the octane number by describing only the octane/heptane mix of the reference fuel. Sometimes they also include environmental junk like lead and alcohol content. It is unlikely that there would be anything about RON and MON, specific gravity / API gravity, RVP, heat of vaporization, energy content, or any other similar factors that would be important for research and development but have no value to a mechanic. I'm not even sure if a chemical engineering degree program would cover much of this other than what is common to all fluids.