Premium Unleaded Recommended for Speed3

[dieseldriver]

Well, I already picked up a Mazda5 (2012) GT few weeks ago but also test drove the Speed3 at the dealership, the one with Tech Package. But I could not help but notice that Speed3, and also what used to be my first choice, the Subaru WRX hatchback requires Premium Unleaded with octane of 91 or higher. What happens when you use something like a mid grade fuel, or even just regular? Is the Premium a requirement or just a recommendation? Thanks.

Who know, in a few years, when I get tired of the 5, might go get the WRX or the Speed3.

 

[chief_wiggum]

requirement; forced induction and direct injection require higher octane.

 

[WillD]

The boost and timing will get retarded by the computer to protect the engine and therefore you will make less power.

 

[dieseldriver]

I see, thanks guys. Would it damage the engine if lower octane is used continuously? I thought the car has way too much power to begin with so as long as the engine runs smoothly... 263 H.P. rating is a LOT for such a small car.

BTW, another question. Am I the only one that thought that gearbox/clutch did not feel precise; when comparing it to German rival like GTI?

 

[WillD]

It isn't a recommendation that you use premium fuel. As you noted it says that premium is required both inside the fuel door and in the owner's manual.

I don't personally believe that engine damage would occur if you continuously run low grade fuel. If someone was able to provide first hand knowledge of running their car (stock) with low grade fuel and problems happening that are related to the fuel I might be swayed. But as it stands, I think the good folks over at Mazda have too many fail safes in the computer to prevent serious damage from occurring. I've run a couple tanks of regular fuel when there was no other option and I did not experience any issues.

That said, I'd be willing to bet that your warranty document would frown upon this blatant disregard of operating instructions should anything actually happen

 

[chimmike]

You'd be foolish to buy a car like this and not run premium fuel. If you can't afford the extra few bucks at fillup for premium, don't buy the car. There are caveats to buying performance cars like this. 18" UHP tires aren't cheap, either, if you want tires that won't suck nuts and slip-slide in the rain or have poor sidewall characteristics.

 

[dieseldriver]

Okay thanks for the information guys. For the time being, I guess I'll have to put aside the idea of the Speed3. But I am going to the dealer in a while to pickup my new plates for the CX9 and maybe I'll steal another ride of the Speed3 (red one with tech package) just to suck out more information and maybe returning the M5GT for it... pipe dreams...

 

[WillD]

You'd be foolish to buy a car like this and not run premium fuel. If you can't afford the extra few bucks at fillup for premium, don't buy the car. There are caveats to buying performance cars like this. 18" UHP tires aren't cheap, either, if you want tires that won't suck nuts and slip-slide in the rain or have poor sidewall characteristics.

Exactly. Don't forget UHP + NJ Snow = Ditch or worse. So a set of winter wheels/tires is another thing to think about.

 

[MSMS3]

Premium octane rated fuels also typically have much stronger detergent, anti-sludge and other additives. These engines need those extra additives, even if there were no need for the extra power. But, as said above, if you don't need the extra power just get a lower power engined car like the 2.5 liter Mazda 3.

 

[chimmike]

Premium octane rated fuels also typically have much stronger detergent, anti-sludge and other additives. These engines need those extra additives, even if there were no need for the extra power. But, as said above, if you don't need the extra power just get a lower power engined car like the 2.5 liter Mazda 3.

Those additives do absolutely nothing for our engines as we're direct injected. Those additves are meant to keep valves clean. Well, since the fuel isn't port injected, it doesn't go over the intake valves, so frankly those 'additives' are taking away precious fuel space in the volume I'm buying! Take off your intake manifold sometime and look at the carbon gunk on them.

Just because the car requires premium does not mean it's significantly more expensive. I get 28-30mpg highway in this car, and with the fuel .30-.40 more than 87, you're only looking at a difference of $3-5 on a full tank 87 vs 93.

 

[MSMS3]

^ I understand your point and generally agree.

But, with respect, not all of the fuel burns from that high pressure DISI shot from the injector into the cylinder. Some of that extra fuel is intended to be purposefully used for cylinder cooling. And if you run catless, as do I, you can tell it's not all burning given the degree of afterfire. But you're right that the fuel never gets a chance to clean the back side of the intake valves or the intake ports where so much of the gunk accumulates. It will still help the injectors stay clean and help the tops of the pistons and the combustion chamber. And stronger additives will help with that.

 

[chimmike]

You don't have to tell me that it's not all burning. I have clear obvious evidence on my bumper.

 

[MSMS3]

^ Amen. And if I were to follow you, I'd probably see visible evidence at night from the afterburn! lol. At least that's what I'm told from running catless.