Running lower octane

[MikeHTally]

I've ran mid-grade and regular, both work fine. This isn't an old turbo, the ECU should be protecting the car from knock. Also, I believe (but could be wrong) that cars for sale in the US are required to be able to run on 87 octane. Wrong - the feds haven't gotten in our shorts to that extent yet. That being said I know tuned BMW's (M3's) run like crap on regular, but that's a totally different setup. Give this engine lower octane and it should just turn down the boost, like it's doing every 1st & 2nd gear anyways. Can't comment much on fuel mileage, as all grades of fuel here are laced with 10% ethanol all winter long, because one @#%$@ county requires it (not mine, but fuel distributors don't care), so it all sucks. Regular may be slightly less than 92 but not enough to be really noticeable or overcome the cost differential.

Come to think of it the 10% ethanol may be helping the knock/boost situation because ethanol has a very high octane rating (one positive to offset it's low fuel density). Either way I only put it in when I know I gotta burn a whole tank stuck in traffic or going slow, I'm feeling poor (which happens a lot these days) and the differential is in excess of 40c/G. Premium is now over $4/G here.

What are we talking about? Less than a penny a mile? Mine is currently running $.15/mile for fuel. I don't think the extra $3 or less per tank is gonna wreck my budget, but I'm pretty sure that regular use of regular will hurt the motor.

 

[oaklandopen]

Mazda didn't know what the **** they were doing....I run tap water in my speed3

 

[MikeHTally]

I tried that, but I went through front tires at about two pairs a month. Had to switch back to the lizards.

 

[flomulgator]

What are we talking about? Less than a penny a mile? Mine is currently running $.15/mile for fuel. I don't think the extra $3 or less per tank is gonna wreck my budget, but I'm pretty sure that regular use of regular will hurt the motor.

40c/g difference is $5 tank @ 12.2 gallons. $5 may not be much to you, but that's lunch to me. Since I lost my job I've started thinking about these things more. Sometimes I know I'm not gonna have any fun with the car, as I'm gonna be in heavy traffic, etc.... I limit myself to about 1/2 throttle, get better gas mileage, run low octane, save on both ends. Regular definitely isn't going to hurt anything at low power levels, and you have provided no evidence as to why it would hurt this car at high power levels. Don't get me wrong, I put premium in it when I'm having fun, but Seattle freeways in pouring La Nina rain on snow tires is neither the time nor the place.

 

[MikeHTally]

$5 for lunch?! Man, I can eat for 2-3 days on $5 and I work ~42 hrs a week. The book says 87 only in emergencies and just enough to get to higher octane. I'll take their word for it. Here, the difference is $.20. That's < $3/tank.

 

[wootms3woot]

Man...I'm glad I took out loans, went to college and acquired a good job...I couldn't live with myself if I thought ~$5 a week was a significant amount of money. The only way I would accept that complaint was if someone drove 350miles a day and filled up 7 times a week.

People who buy $24,000 turbo cars and then complain about chump-change need to re-prioritize their lives...

Sorry if I sound like a dick, but it's so annoying when people make irresponsible decisions and then complain about them. jus sayin'

 

[b e z]

I dont know if any of these were directed towrads me since i did bring up the question but i have no problem affording gas whether it be 87 or 93. I was more or less complaining that prices are high and seeing if running 87 would hurt anything. I agree that if you bought this car and you have trouble affording the appropriate things for it then you need to re- prioritize but there are some people who bought this and then lost their jobs so can no longer afford some more expensive things ( not talking about myself here).

 

[wootms3woot]

It's never a good idea to run low octane in turbo or high compression applications, you run the risk of spark knock. Premium combusts at a higher temperature than regular thus lowering the chance of knock. The knock sensor can sense knock and retard timing, but that's just wasting useable power. Fill up with premium and you can be confident you will always have full use of your car's potential. Plus premium burns a little cleaner due to added detergents, so your valves stay cleaner longer. And we all know how rich the DISI motor runs...every bit helps I guess.

 

[oaklandopen]

Its not about the temperature it takes to ignite the fuel, it about the way the fuel burns. More like faster and slower burn, or how much energy it takes for it to burn

Higher octane equals more energy needed to burn

There are 2 different arguments going on here. One is about how someone buys a high performance, high price car relative to relative to the other models among the same line (ie mazda3 2.0 or 2.3) and try to cheap out on everything else to "save a buck."

Really? Are people really going to just say **** it to the recommended fuel (and who knows what else) to save substantially less money then what they might have to spend later in repairs? Owning a car is more than just the sticker price! Maybe ill buy a bugatti veyron and switch the wheels and tires with some extreme lightweight wheels wrapped with 195 series rubber. Less rolling resistance means I can squeeze out a couple more tenths of an mpg

The next argument is about how it would or would not do damage to use lesser octane rating. Well, not only will you increase the chance of knock, and that doesn't mean at only wot, your computer is going to go crazy changing the timing back and forth even more now that the fuel is not up to par. So therefor, if your ecu can't find a sweet spot, the fuel usage is going to be all over the place. That means you run the risk of getting worse gas mileage

So if one is getting worse gas mileage than they are saving by paying for a lesser octane....then s*** just cancels out doesn't it

And actually, there is a 3rd point to be brought up. And that is that I'm glad I buy new and not used

 

[MS6S2K]

I ran 87 octane once in my former ms6, and it ran just fine. HOWEVER, I was also on a long highway road trip cruising at 70mph with little boost. I'd never run 87 normally, but in reality, if you wanna run low octane, then you need to not drive it hard or fast. On other words, use high grade.

 

[t147]

running a lower octane in a forced induction engine WILL cause Detonation and possibly Pre-ignition. Just because you're knock sensor isn't reading enough knocks to throw a CEL doesn't mean it's not happening. Over a long period of time runing less than 91 octane fuel will damage piston heads and deck surfaces and the depressions of heads and block expecially under periods of boost.

 

[flomulgator]

Just because an engine has a turbo on it doesn't mean it will knock. There are many variables that go into producing pre-ignition, and cars are getting consistently better at avoiding knock events. For starters, if you get knock a modern car won't throw a CEL, it will just adjust injection timing and boost and valve timing (if available) on the fly. Knock sensors are very reliable at low RPM's, less reliable at higher RPMs (due to background noise, as it is essentially a microphone). When knock issues on a turbo are dangerous is when you are running WOT near readline, for the previous and other reasons. If you want do that, fire and forget without worrying about it at the drop of a hat, then I highly recommend you run premium all the time. If you can keep within some basic guidelines and have a reason/need to do so, I think you're fine running 87 or 89 for a while. If you don't believe anything I just said than remember this: It's a passenger car for sale by a major OEM in 2007+ that people have a reasonable expectation of the engine lasting 100,000 miles without any grief whatsover. 264 hp out of a 2.26L 4 may seem like a lot compared to other cars for sale in it's class but the reality is compared with the larger car universe this is a very conservative tune with a smallish turbo built for reliability.

 

[t147]

No, there really aren't that many factors when it comes to detonation. Wrong fuel, wrong timing, too much fuel(maybe/doubtful) that's about it. Lean conditions burn holes in pistons and burn valves, hard start etc. Too much fuel can crack a piston, bend valves( liquid is incompressable), lack of power, fuel in oil, hard start, etc. I can keep going but pre-ignition is caused by the AFR being ignited too early by a glowing piece of carbon build up, or extreme cylinder temperatures and Detonation is the compression of the AFR igniting without a spark pretty much always caused by too much fuel, a dead plug, too far retarded or too much advanced timing(it probably wouldn't run in this case or have any power if it did).

Bottom line, too low octane fuel will cause damage in an engine not meant to run it(the 2.3l T/C Dizi engine in this instance). Our timing, AFR, and overall performance rely on it. At only 3.00 extra per fill up, this thread shouldn't even be open.

 

[oaklandopen]

Regardless of how good modern cars are at preventing knock/detonation/preignition, the knock sensor is still a REACTIVE system, not PROACTIVE. So knock happens all the time, its just going to be more so with a letter octane

 

[gtlaw]

buy a prius, and carpool with your life partner

 

[MikeHTally]

To quote Kain, "LAWL".

 

[Mike240SX]

40c/g difference is $5 tank @ 12.2 gallons. $5 may not be much to you, but that's lunch to me. Since I lost my job I've started thinking about these things more. Sometimes I know I'm not gonna have any fun with the car, as I'm gonna be in heavy traffic, etc.... I limit myself to about 1/2 throttle, get better gas mileage, run low octane, save on both ends. Regular definitely isn't going to hurt anything at low power levels, and you have provided no evidence as to why it would hurt this car at high power levels. Don't get me wrong, I put premium in it when I'm having fun, but Seattle freeways in pouring La Nina rain on snow tires is neither the time nor the place.

Not to be a smartass, but if you've lost your job what sort of mandatory driving might you have to do? The $5 a tank could be made up by driving less.

If driving less is not an option and $5 is still a life-changer, it's definitely time to get into a different (read: used & cheap) car.

 

[t147]

Regardless of how good modern cars are at preventing knock/detonation/preignition, the knock sensor is still a REACTIVE system, not PROACTIVE. So knock happens all the time, its just going to be more so with a letter octane

I actually meant to add that in my post... Thank you.

 

[Preferio]

buy a prius, and carpool with your life partner

LOL

Anyway... The one time I ran low octane, it ran like s***. But then again, it could have just been a placebo affect. After that I decided to just run premium every time. Realistically it comes out to an extra $3 per tank. If you can't financially support spending an extra $3 on a tank of gas, you fail at life.

 

[slavrenz]

Its not about the temperature it takes to ignite the fuel, it about the way the fuel burns. More like faster and slower burn, or how much energy it takes for it to burn

Higher octane equals more energy needed to burn

There are 2 different arguments going on here. One is about how someone buys a high performance, high price car relative to relative to the other models among the same line (ie mazda3 2.0 or 2.3) and try to cheap out on everything else to "save a buck."

Really? Are people really going to just say **** it to the recommended fuel (and who knows what else) to save substantially less money then what they might have to spend later in repairs? Owning a car is more than just the sticker price! Maybe ill buy a bugatti veyron and switch the wheels and tires with some extreme lightweight wheels wrapped with 195 series rubber. Less rolling resistance means I can squeeze out a couple more tenths of an mpg

The next argument is about how it would or would not do damage to use lesser octane rating. Well, not only will you increase the chance of knock, and that doesn't mean at only wot, your computer is going to go crazy changing the timing back and forth even more now that the fuel is not up to par. So therefor, if your ecu can't find a sweet spot, the fuel usage is going to be all over the place. That means you run the risk of getting worse gas mileage

So if one is getting worse gas mileage than they are saving by paying for a lesser octane....then s*** just cancels out doesn't it

And actually, there is a 3rd point to be brought up. And that is that I'm glad I buy new and not used

That's really the only argument that needs to be made. Here, 91 octane is about 5% more than 87 octane. If you get 10% poorer mpgs as a result of using 87 octane, then it's actually more expensive to use the lower octane gas!

Simple numbers, people - we don't need to be arguing about each other's financial predicaments.