What octane to run?

[SilentSno]

The only way a car will make more power on higher octane is if the ECU advances and retards timing using sensors determining fuel used.

I'd believe thats why the Porsche made more power, and to my knowledge, the MP3 doesn't have this type of sensor.

EDIT: Actually the MP3 could actually "Read" the exhaust with the O2 sensors and maybe determine fuel octane that way, but still unsure if the ECU would advance/retard timing. I know it would if a knock occurred.

Fuel burns, it doesn't explode, exploding fuel is detonation.

Lower octane fuel burns faster, Higher octane slower.

 

[SilentSno]

On a side note, this type of discussion and how every is acting like adults is why I've always loved this forum. I've been dormant for a while, but I appreciate everyones maturity. (yippy)

 

[Bernout]

i notice a difference in performance just going from mobil 93 to shell 93

not on the mp3 but on the motorcycle(older suzuki 650)....

i switched every 2 tanks for awhile(1 tank=150mi).. mobil would only pull up the front end in 1st gear try after try...while the shell v-power could constantly pick up the front end in 1st AND 2nd gear.(and im a good bike driver). and after 2 weeks of mobil and only 1st gear lift off... you pick up second gear leaving the shell parking lot.

so at least its proven to me that gas COMPANIES are different and have the SAME octane..... i have to assume that 85.5 and 93 would give different performance as well.... sensors or not

 

[70]

The only way a car will make more power on higher octane is if the ECU advances and retards timing using sensors determining fuel used.

I'd believe thats why the Porsche made more power, and to my knowledge, the MP3 doesn't have this type of sensor.

EDIT: Actually the MP3 could actually "Read" the exhaust with the O2 sensors and maybe determine fuel octane that way, but still unsure if the ECU would advance/retard timing. I know it would if a knock occurred.

Fuel burns, it doesn't explode, exploding fuel is detonation.

Lower octane fuel burns faster, Higher octane slower.

Yeah, the Porsche does have individual knock sensors in each cylinder, so they can get very precise on the timing in each and every cylinder to maximize performance.

The MP3 has a knock sensor. Somewhere. Under the hood I think.

 

[SilentSno]

i notice a difference in performance just going from mobil 93 to shell 93

You can definately get different performance from different companies. They both have unique ways of creating their fuel and have certain additives, etc.

 

[Tzar177]

You can definately get different performance from different companies. They both have unique ways of creating their fuel and have certain additives, etc.

Well on that note....who has noticed the best performance on whos gas in our mp3's?

 

[JoeManNorth]

I usualy run Petro Can or Sunoco, I rarely run Shell, I've heard bad things about shell messing up your pump. I'll put Esso (Exxon) sometimes, but I've never really paid attention to a difference in preformance. I know when my tank is empty I run faster, but that's common knowledge.

 

[JoeManNorth]

Oh.. and it's Petro 92 and Sunoco 94.

 

[Kremlinist]

Just a warning, and a side note.

Just a heads up, my motor blew at 92k, I used 87 most of the time, except when gas was relatively cheap. I'm not saying that I know the cause of my motor blowing, but its a distinct possibility, I think, that using too low of an octane and causing knock could have caused my rod knock. I don't know car engines like I know airplanes, you have to be anal about your octane with aircraft, there are no knock sensors besides your ears in most airplanes. As a note, since our cars ask for 91 octane, as I understand it you can use 89 half the time and 93 half the time and it will average out to 91 (since octane measurements are an average anyway).

 

[323]

so i was curious of what the car manual would say so i just looked it up

*2.0-liter engine (Special Edition)
Your Mazda will perform best with
premium unleaded fuel having an octane
rating (antiknock index) of at least 91
[(R+M)/2 method].

You may use a regular unleaded gasoline
with a rating from 87 to 90; this will
slightly reduce performance.

 

[SilentSno]

Just a heads up, my motor blew at 92k, I used 87 most of the time, except when gas was relatively cheap. I'm not saying that I know the cause of my motor blowing, but its a distinct possibility, I think, that using too low of an octane and causing knock could have caused my rod knock. I don't know car engines like I know airplanes, you have to be anal about your octane with aircraft, there are no knock sensors besides your ears in most airplanes. As a note, since our cars ask for 91 octane, as I understand it you can use 89 half the time and 93 half the time and it will average out to 91 (since octane measurements are an average anyway).

What happened when the motor blew? Have you owned the car since new? If not how many miles did you run with 87? Here in montana our "low" grade is really low, 85.5 and I've been using it since Fall 2003 around 30k miles, no issues. Only mods are in my sig.

You'd hear the engine knocking before it blew if that was teh cause, and the mechanic working your car should have a general idea what he thinks happened. There a million reasons why an engine could blow and I doubt it had to do with the octane, as running too low of octane for extended periods of time would have caused it to blow a lot sooner.

Extremely true for me as I have auto-x mine super hard the past 2 years.

 

[SilentSno]

On another side note these engines seem to really like to consume oil after its been really broken in. So much that you could use 3 or more quarts of oil before your next change, so its possible that could have been a cause of your blown engine.

See this thread for more oil consumption info:

http://www.mazdas247.com/forum/showthread.php?t=123662370

 

[MP3 Abuser]

Uh well, I have over 115K miles on mine. It uses zero, zip, zilch, nada oil between changes, I run 87 except when the oil companies don't feel like giving us the big, throbbing, veiney, dry one, which nasn't been for some time out here in bend over and take it Cali!

I work at least one and mostly 2 days a week at Mt. Wilson, which is right next to the famous Angeles Crest highway, home of every magazine test when it comes to testing handling performance for cars and bikes. Also home to a few midnight rice racer meetings I've stumbled into on the way to work.

Those suckers think they can go fast without knowing the road. I regularly embarrass STI's and the like who think they can catch me! So, I put the hurt on the little thing some times making these power hungry fools overshoot turns and get outta shape.

Then again, I'm not what seems to be the typical MP3 owner as mine is totally bone stock. Heck it's still got the original timing belt in there. (though I am getting ready to finally change it) I still have stock brakes too! I just got around to buying some EBC rotors and pads for the front, but that's only because I have thoroughly abused the stockers and I'm sure they are out of spec.

 

[Tzar177]

How is it that you don't use any oil between changes? what kinda oil and filter are you using? I have some blow by but not enuf to warrant the adding of more oil between changes

 

[323]

Uh well, I have over 115K miles on mine. It uses zero, zip, zilch, nada oil between changes, I run 87 except when the oil companies don't feel like giving us the big, throbbing, veiney, dry one, which nasn't been for some time out here in bend over and take it Cali!

I work at least one and mostly 2 days a week at Mt. Wilson, which is right next to the famous Angeles Crest highway, home of every magazine test when it comes to testing handling performance for cars and bikes. Also home to a few midnight rice racer meetings I've stumbled into on the way to work.

Those suckers think they can go fast without knowing the road. I regularly embarrass STI's and the like who think they can catch me! So, I put the hurt on the little thing some times making these power hungry fools overshoot turns and get outta shape.

Then again, I'm not what seems to be the typical MP3 owner as mine is totally bone stock. Heck it's still got the original timing belt in there. (though I am getting ready to finally change it) I still have stock brakes too! I just got around to buying some EBC rotors and pads for the front, but that's only because I have thoroughly abused the stockers and I'm sure they are out of spec.

lol your funny. handlin power! this thread got me scared so i went n checked my oil and it was full

mines got low miles tho. 46k

 

[BondoBob]

Damn, does everybody treat their MP3s like a rented mule?

I have 83,500 as it sits in the driveway tonight and have run regular (87 octane) for most of the life of the car. I ran premium back in 2001 and found no difference in performance. I don't use any oil between changes (every 3000 miles - with Castrol syn) either. I'm still on the original clutch and I haven't grenaded the tranny either.

 

[cbutters]

I used to always fill up with 87, till i read in the manual that it recommends 91 because of the advanced timings. So I started using 91, Im sure that Mazda engineers wouldnt recommned it for nothing.
Also, I notice a marked improvement in my gas milage running 91.

Article on octane:
"A common myth amongst petrol consumers is that adding a higher octane fuel to a vehicle's engine will increase its performance and/or lessen its fuel consumption; this is falseengines perform best when using fuel with the octane rating they were designed for and any increase in performance by using a fuel with a different octane rating is minimal or even imaginary."

I have noticed that yes my gas mileage is better on 91 than 87, I am getting 20-30 more miles on it that the 87.
If you take the difference in price between the two $3.38 (87 octane) vs $3.48 (91 octane), and the difference in the mileage is 375 vs 400 miles on a tank.
so for 13 gallons of gas, 87 costs $43.94, 91 costs $45.24

Octane 87 costs $43.94 divided by 375 miles driven costs 11.7 cents per mile
Octane 91 costs $45.24 divided by 400 miles driven costs 11.3 cents per mile

In my observations and calculations, it seems that getting the 91 gas ends up making gas cheaper in the long run, due to the fact that our engine performs optimally and can pull out better gas mileage numbers. That is why I buy 91.
So my advice would be, go with the recommended octane, 91, trying to save a few cents by buying lower octane gas will only be eaten in the fuel efficiency that you could have achieved with the 91.

If you have a honda accord or civic, a lot of model years are actually are more efficient and powerful at 87 octane than the 91, so this advice i gave above is purely for the MP3.

 

[SilentSno]

Just to add,

I just recently starting noticing that I've been using oil. But I have been bit hard on her, racing Autocross. So it's been heated up pretty good.

Also with the mods I have currently, see sig, I get around 27 - 28 MPG in town driving, this all on 85.5 octane. I don't take her on highway trips much anymore.

 

[MP3 Abuser]

I was using the Castrol Syntec blend up until it had about 90K on it. I've been running the full synthetic stuff since and use plain ol Fram filters. I will add that I am very careful to keep it away from the redline. There's not much power up there anyway, so no need to rev it that high. 3000-5000 seems to be the sweet spot for me.

 

[CBD03]

I am sorry to bump a kinda old thread but,... I am kinda new to the whole MP3 thing. I was wondering,.. what exactly are all of the differences, in and out, between the MP3 and a normal protege 2.0 engine? Please use technical terms so I can learn more about it. Thank you in advanced.