1987RX7guy

iTrader: (3)

Evil Aviator-quoted the US manual. That is good enough for me.

eViLRotor

iTrader: (2)

Oh, I'm not doubting EA's sources. In fact, he's one of the most reliable people on here.

Its just interesting to note that the same car, can have such a variation in recommended octane...

Wankel7

Lol, one of the few folks that would even know what Jet A is

Oh yea. On the '86 Base I run 87. Before I was educated I ran 91. And when I switched it was noticeable.

On the 91 TII I run 91 octane.



James

BlackRx7

I believe octane ratings where differn't for the turbos depending on the year 87-88 lower compression rotors, less octane, 89-91 high compression, higher octane makes sense. Though I have never seen an 87 TII onwers manual, just heard through the grape vine that it said to use 87 octane.

Maybe its the fact that I'm street ported and have more volumetric efficency, more cooling due to more suface area of the intake and exhuast ports.

Also maybe its because I'm running 4 trailing plugs (colder spark less chance of detenation)

Or is it because I'm running a walbro fuel pump?

Whatever it is my car runs the best on 87 octane pushing 7-8psi, intake, 2.5 full exhuast, port matched turbo runners and ported wastgate.

I just ran it at the track on the 87 and ran a 13.5 at 103 with a bad clutch I was still running rich too, full boost at 3000 rpms and it holds it untill 7000

OnlineAlias

Octane lowers the flash point of fuel. The lower the flash point, the higher the resistance to pre-detonation, or pinging.

The higher the absolute pressure of the air fuel mixture, either through higher compression ratio, boost, or volumetric efficiency, the more propensity an engine has to pre-detonate.

In higher elevations, engines have less volumetric efficiency, and require less octane due to lower combustion pressure.

Rotary engines, due to their combustion chamber rotating on its axis, have high resistance to detonation, and require only low octane fuel.

Jet-A, which is really just kerosene, has a VERY low flash point, wouldn't ignite by the spark plug, and therefore wouldn't even start the car.

BlackRx7

very nice observations OnlineAlias

1987RX7guy

iTrader: (3)

Wait

WOuldn't octane make the flash point higher? meaning the pre-ignition temp would be higher thusly resisting detonation MORE? I am just trying to understand this don't take it as an arguement

BlackRx7

no no, a high flash point is from lower octane, lower flasher point is from higher octane

kinda like leaner is hotter combustion
and richer is cooler combustion

Evil Aviator

Is that octane rating Research Octane Number (RON) or Pump Octane Number (PON, aka the R+M/2 method)? Also, Canada may have less quality controls on their petroleum products, and therefore Mazda may recommend a higher octane for safety.

I always recommend that non-US forum members list their country of origin in their "location" at the left of the screen because otherwise everybody assumes that you are in the US, and some things are not the same. For example, the US octane rating is not the same as most non-US octane ratings, the US quart is not the same as an imperial quart, $1 USD is not the same as $1 CAN, etc.

I have owned both an 88 NA and TII, and can verify that the US manual lists a minimum octane rating of 87 (PON). Jerry Harding has verified the same with the US S5 manual.

Assuming that the engine is somewhat stock and in good running condition, it will work just fine on lower-octane fuel. There is nothing wrong with using higher-octane fuel, other that it's a waste of money if you don't need the extra anti-knock properties. I'm not sure about the other countries, but the US has certain standards for fuels, and all US octane grades have detergents, additives and whatnot, but the oil companies only advertise this about their high octane fuel in an attempt to make the consumers think that only the expensive fuel is good for their engine. Higher octane IS a good idea for some modified engines, some engines that are in poor shape and/or out of tune, and all highly-boosted engines.

The fuel octane rating isn't raised, the octane requirement of the engine is lowered. Does that make more sense now? Anyway, it's not necessarily a whole 2 octane numbers, and may be next to nothing, depending on the engine and amount of altitude change. Also, because of this octane requirement reduction, some oil companies re-state their octane rating to a higher number in high altitude areas, so you need to be careful about what you are actually putting in your tank and where you drive after filling up the tank.
http://www.imoc.co.uk/technical/article/octane.htm#q31

ilike2eatricers

good write up evilaviator

ViperKillerWannabe

I've been running regular in mine (S5 NA) for about 4 or 5 months now, and just last week I put in some midgrade just to see what would happen. It seems to idle a little more smoothly, and pull a little harder. Is this change only temporary? Should I switch back to regular?

BLACK ROCKET

I've always use mid-range gas and works great. I tried higher octaine gas, but, there were no impressive improvement. So, I stick to the mid range.

BlackRx7

okay now a REAL question j/k,

how many points are there to an octane number? when you buy octane additives it say will raise up to 17 points or 1-2 octane numbers

ViperKillerWannabe

The way I understand octane booster, is one bottle is one point. So if you need more than one point, use more than one bottle.

Evil Aviator

One point = 0.1 octane number. Therefore, 17 points = 1.7 octane numbers, which would in fact fall between the 1-2 octane numbers as you have stated. Most octane boosters only add 4-7 points (0.4-0.7 octane number) increase. For example, adding a 7 point octane booster to your 91 octane gas would yield 91.7 octane gas. Obviously, this is a rip-off at $8 per tank for the treatment. Therefore, save your money for something that is actually useful, and leave the octane boosters to the Ricers.

If you add a bunch of bottles of octane booster to your fuel tank, it can eat away your fuel system, and possibly harm your engine. Not good.

BTW, if you guys ever want to know what they put in this junk, just ask for the MSDS (MATERIAL SAFETY DATA SHEET).
http://householdproducts.nlm.nih.gov...ueryx=Additive

jreynish

iTrader: (2)

I run 91 -93 ocatane because i am boosting 15psi!!!
but if was running stock it would be 87-89 octace for me that is here in canada!
And as far as i understand the us and canadian octance per fluid once is the same regulations. I could be wrong if so somone please correct me, but last i read it was the same! just a little bit of info

JerryLH3

iTrader: (11)

Hey, don't drag me into this!

Yes, the US S5 manual (my 1991 to be exact) states "Your new Mazda is designed to obtain maximum performance with UNLEADED GASOLINE with an octane rating (anti-knock index) of 87 or higher (using R+M/2)."

It makes no differentiation between turbo or non, but they do say "or higher." Take it for what it's worth. Mazda says your stock car can run on 87.

3RotorRocket

94 Octane nothing less on my TII

RunningDeer

89 octane for my S4, cuz anything less and she runs like crap.

lnbrown5981

i run 89 on my s4 na only because i have my timing advanced 10 degrees. i also use jp-8 when available

rotary>piston

my N/A worked great on 85. I could actually feel a slight loss in power with 91.

BioNuke

octane RAISES the flash point of the fuel, meaning that it takes a higher temperature to detonate without a spark. also higher octane fuel burns a little slower, and a little hotter than lower octane fuel... I tried running premium (91 here in socal) in my 88 'vert, and it was awful. it idled fine, but i got alot of surging in the acceleration (less power, and really uneven). I tried it to see if the increased pressure (from higher combustion temps) outweighed the slower burn rate, and apperently it didn't. If I was boosting or messed with the timing so it started burning earlier I would try it again to compare to regular (87), but until I do my turbo swap I'm stickin with regular...

oh blackrx7, you said that you are running 4 trailing plugs for lower spark temp. why would you want a lower spark temp? once it sparks, the fuel is supposed to burn... I'm not trying to flame, I just wanted to understand cuz maybe you know something I dont...

Erk

heh... 87 here on my NA, to poor for 91.

guitarbarb87rx7

What is the difference between 89 and 93 ?

KILLA_B13

Same!