Couple of gas questions
 

I know you all hate rehashing old subjects, but I have been unable to find a concrete answer anywhere on the forum, and probably won't get one here, but will try anyway.

When running a near-stock Turbo II, what is the recommended Octane to run? I am running 91, and have been since I purchased the car. The previous owner also ran 91 from the day he purchased it, and advised me to do the same. Previous owner is a close friend who has been driving nothing but rotaries for about 6 years. I am new (coming up on 3 months), so I am still green to everything, so please forgive my ignorance.

So.

1) Will running 91 octane on a TII increase carbon deposits?
2) Is running 91 necessary? Or will 89 do? Or even 87?
3) Is Ethanol blended gas bad for the engine. I ask because there is a gas station here that sells 94 octane gas, that is Ethanol blended, and have been tempted to purchase, but am unsure of what to expect for results - probably nothing at all, but still.

i am wondering the same exact thing, getting a little bit expensive with gas prices deez days to run 91 lol!

ive heard on n/a, lowest is best, on t2, 91 or so is good

??

the lowest octane fuel I can buy at a station is 92 octane ...

I run my FCGTR on 98... with N/A there's no reason to push up the octane, but on a turbo ... there are people in Australia who would freak out if all they could put in to their engine was 91 octane ......... it may not be necessary, but for the cost of a couple of dollars; with the fuel readily available, I don't see the point of running my car any lower then 95 octane.... commonly available here but as I said, usually off 98.


Guess doesn't do anything to answer your question .. was just sorta surprised; is high octane fuel not common over there?

not here in the us....i know in sweden where i used to live standard was either 95 or 98....not sure, i was a kid then.

A little fuel 101...

Octane does NOT add power, it only adds knock protection (or compressibility). Adding 95 or 100 octane fuel to a motor that isnt set to run it will not release any power, it will only inhibit it (slower flame front).

there was some discussion about this a month or two ago, where it was stated that the Mazda rating for a stock TII was 87 octane. I dont have the owners manual handy so I cant verify that statement, but what I can say for certain is that for a stock TII, 91 is MORE then adequate.

Now on to Ethanol...

The Ethanol blended gas is dependent on the ratio. E85 is NOT going to work in your car, but 10% blend will probably not make much of a difference... What is the blend for the 94 octane that they sell?

Not sure... will look into it. Yeah, I definitely don't run 91 octane thinking it will give me more power... Purely for protection against detonation.

octane ratings in different countries generally translate into about the same actual qualities, its just the measurement systems that are different.

that said, a stock TII can run just fine on 87 octane. 91 wont hurt anything, but its basically just a waste of money.

i run 91 or 93 octane in my TII, with high compression(9.4), at 14 psi, daily driven.

there is a trend on this forum to run much higher octane than is necessary. as long as it is tuned right, your car wont detonate on pump gas unless you make some SERIOUS power.

basically, what i'd say is:
0-8psi 87
8-12 89-91
12-16 91-93
16+ race gas

pat

ps 94 octane doesnt have enough ethanol in it to hurt anything.

my 88 TII owners manual specifically states that 87 octane is the correct rating of fuel to use

Is this statement based factually? If so, I would like proof.

Rat

I have a mechanic friend who has been running 87 on his (stock except for the old style-RB exhaust) S4 TII for 174K (Since it was new) and it still ran fantastic when he sold it (at 174K) and I've talked to the new owner since and it is still running great. Still original engine, and it was driven pretty hard.

I would not run Ethonol (E85) on a stock RX-7 because it eats rubber (IE: The rubber fuel lines). Also, it runs at a different fuel ratios then gasoline, and your O2 sensor will be wildly inaccurate as it is calibrated for Gasoline at 14.7:1.

E85 is compatible with most, if not ALL stock fuel system lines, but you are 100% correct about the other points. It requires almost TWICE the amount of E85 to do the same amount of work as regular gas. So in order to run a Rotary on E85, you would need HUGE injectors and a REALLY BIG FUEL PUMP... Also, correct is the mixtures, as the stoich on E85 is about 9.8:1, so you would need an 02 sensor capable of running in those areas (I believe the UEGO cuts off at 10:1).

Seriously? E85 is OK with stock rubber?

How do you know? I heard it was bad for rubber from a few friends whos specialty is alternitive fuels.

But you know, I might have just got it confused with some other form of fuel.

Ok, so 87 is fine to run on a nearly stock TII? Shit I am so nervous about putting 87 octane in the car for some reason... Like, I'm scared... but shit, at $1.21 per Litre, ouch. I could use the $0.10/L savings, especially at 15mpg. :o

My 98 TII manual says this:

"Your new Mazda is designed to obtain maximum performance with UNLEADED gASOLINE of 91 Research Octane (RON + MON)/2=87 or higher when the engine is adjusted to factory recommended specifications."

So does that mean 91 or 87 octane?

Check this out, from Wikipedia:

The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel through a specific test engine with a variable compression ratio under controlled conditions, and comparing these results with those for mixtures of isooctane and n-heptane.

There is another type of octane rating, called Motor Octane Number (MON), which is a better measure of how the fuel behaves when under load. MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, a higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern gasoline will be about 8 to 10 points lower than the RON. Normally fuel specifications require both a minimum RON and a minimum MON.

In most countries (including all of Europe and Australia) the "headline" octane that would be shown on the pump is the RON, but in the United States and some other countries the headline number is the average of the RON and the MON, sometimes called the Anti-Knock Index (AKI), Road Octane Number (RdON), Pump Octane Number (PON), or (R+M)/2. Because of the 10 point difference noted above, this means that the octane in the United States will be about 4 to 5 points lower than the same fuel elsewhere: 87 octane fuel, the "normal" gasoline in the US and Canada, would be 91 in Europe.

I may be eating my words on this one..

So does that mean that in Canada/USA 91 octane is the correct octane to run?

I ran 92 octane for a while, then switched to 89 octane recently, I have seen no ill affects so far. Also, all our gas here (Chicago, IL) can contain up to 10% ethanol. I have aftermarket intake, downpipe, FCD and exhaust, so I'm not quite stock either. If the original owners manual gave 87 octane the OK, then I'm guessing we have a bit of leeway, so Im not too worried about running 89. These are all US octane ratings, just to limit confusion (I know this board has a pretty international flavor).

I think it means that 87 is the correct recommended octane. The manual said 91 Research and then gave the RON + MON/2=87. The article makes me think that 87 is correct here in Canada/US.

Ha Ha. That should have been 89 TII manual! Freudian slip I guess!