Ok, stupid question. I was at the gas station and some guy was putting in 91 in his RX-8. I know in my NA, i ONLY ran 87, anything more was a waste of money. Does Mazda recommend 91 or was this guy just being an idiot?

Mazda reccomends 91 octane for the rx8

Mazda recommends is but is not required, the manual says that reduced performance will result from using lower octane.



The RX-8's ECU advances ignition timing agressively, that's the reason for using high octane. If lower octane is used the timing will be less agressive resulting in less power.

I always use 91 too...

and will slightly increase the chance of detonation!

Sorry, i just hit reply and it came out like that...



I wouldn't worry about detonation in the RX-8, the ECU is super smart and will retard timing at the slightest hint of detonation. There are a lot of people in the rx8club forums that run 87 octane with no problems at all.

you kidding? i've talked to lots of rx8 guys that ping their motors left and right. the ecu is good, but it's not THAT good. the apex seals are just more resistant to detonation than the old ones.

One of the things I heard (and read some time long ago) is even if your ECU can keep up with detonation, and the 8's is pretty good, you will give up some power and thus some MPG. (as if tracking mpg in an RX8 is a practical thing to do!) https://www.nopistons.com/forums/pub...1047683785.gif



My 8 (the one my wife let's me use sometimes) lives on 91, not willing to scrimp pennies for potential power loss or worse, hidden mystery damage later. https://www.nopistons.com/forums/pub...1047683664.gif



I say this as an owner, not just cause I work at Mazda.



Neil

actually, the lower the octane, the more power it'll make under a given set of conditions (of course staying away from the detonation threshhold). but the rx8's ecu is all nutty, so that might not be applicable.



i run my fd on 87 octane at 8psi ~300-310 whp. and i don't have a hint of detonation. $.20 a gallon savings on gas is nice.

the rx8 we play with gets 91 when it goes to the track, but otherwise it gets 89ish. 22-23mpg highway....



mazda rotaries are kinda funny like that.



the fd has 3x the power and 2x the milage of a 73 rx2, but reliability is the same.

i'd like to see dynos of an rx8 with 87,91, and 100+ octane fuels, to see what the computer does with it.

That would be a cool Dyno day project. I'd be willing to take part in that some time. My car is still stock in the intake and exhaust. No time in immediate future, but definatly open later. I'm in Seattle area, we have enough * owners we should be able to get a few together when the clubs out here arrange a day again..



neil

i'd just be concerned with how long it would take the computer to adjust for the octane. if, in fact, it does.



i somehow doubt mazda would be willing to release the criteria for any possible octane learning mode in the computer.

OK, I'm just a parts guy so take this with a grain of salt.. (Or like Mark Twain said "Better to remain Silent and thought a fool, than to speak up and remove all doubt.") https://www.nopistons.com/forums/pub...IR#>/blush.png But anyway...



There is a knock sensor on the car and my presumption is that it takes no time to learn anything as the computer is responding to the Sensor, along with the other feedback. I am sure the more tech types can take this further, but I expect any differances that can be measured will show ASAP. Older Rotaries actually can do quite nicely on 87 if tuned to it.



Higher Octane means a slower burn as most of you know. In Airplanes with such a huge bore and surface area, it is necessary to get a relatively even burn along with the 2 spark plugs. We do have a strange large surface area thus the leading and trailing plugs.



On my old RE5 Suzuki Rotary Motorcylcle, It had only one plug but was fired twice as I recall..



oops... the old fool has spoken.. https://www.nopistons.com/forums/pub...DIR#>/cool.png

neil

i'm not sure how much power can be built with octane alone on these motors. they already run a LOT of timing to begin with.



leaner with less timing would build more power over richer/more timing.



but it's still something i'm curious about.

Mine pings on 93 in hot days.



The ECU only pulls timing back a maximum of 5 degrees under detonation. So it does little to no good I can let it knock for as long as I want. Ive been pissed off and held the pedel down for over 5 miles with it detonating so much it couldent rev over 5 grand and slow as ****. Just because I hate my motor.



The FE is said to use higher octane because of the higher compression and advanced timing as stated.



Alot of times in the winter and if I get good gas I can run 87. Shity gas at pumps allot as each county has there own set of aditives they feel you should run.

i was leafing thru the 93 rx7 service highlights book (it explains how each system works, plenty of neat graphs etc, there is a very detailed book for the rx8 too), and the fd book mentions that the ecu compensates for the octane of the fuel. it also says the knock sensor retards a maximum of 7 degrees.



i do not see how else it would know what octane is used, and 7 degrees doesnt seem like enough of a difference to compensate for the fuel AND have a saftey margin. i do know that the fd's are tuned so that the do run on 87 just fine.

did you buy the book or are the service highlights (for the rx8) online yet?

there are kinda 2. theres the yamaguchi rx8 book



and then theres a service highlights book, its like the fsm but explains the systems in detail, lots of graphs.

its available as a book. shoot me a pm, i'll get a part number and price, mazda turns the website off on the weekends

oh i was just hoping to DL it for free :p



but i'll pay if i have to. i do enough with the rx8's now to make it worth it.

not sure if anyones got it online. mazda has all the manuals online, but not those

the 0fizzle book is 9999-95-102f-04



the oh-sickness book is 9999-95-102f-06



the 06ness book is pretty short, automatic is new, and is about half the book, and the smart keyless deal is another bit

Ok, so i know its waaay off topic, but are there any plans for major/minor change RX8 next year? or will it be for 08?

havent heard anything offically, but then we usually dont. thats the rhoumour though

It seems that when I run less than 93 octane (which is available in Louisiana) in my 8 the engine makes a god awful knocking noise & some power loss is experienced. I don't use less than 93 anymore for that reason.