Premium gas, or?

[Allch Chcar]

Originally Posted by Subie

It also says this on page 420:

That doesn't specify which octane though.

Okay, it's right above that.

The engine is designed to operate at maximum performance using unleaded gasoline with an octane rating of 93 AKI (98 RON) or higher. If 93 AKI (98 RON) is not readily available in your area, unleaded gasoline with an octane rating of 91 AKI (95 RON) may be used with no detriment to engine durability or driveability. However you may notice a slight decrease in maximum engine performance and you may hear some knocking (pinking) of an engine while using 91 AKI (95 RON) fuel. Use of 91 AKI (95 RON) fuel will not affect your warranty coverage.

So it does knock with 91 but it's still covered under warranty. That is a better explanation to me.

[Subie]

Originally Posted by Allch Chcar

That doesn't specify which octane though.

Okay, it's right above that.



So it does knock with 91 but it's still covered under warranty. That is a better explanation to me.

I interpreted it as meaning that the level of knocking with 91 octane will not be severe enough to damage the engine but that gasoline with an octane rating less than 91 can cause "persistent and heavy knocking, which can damage the engine." Therefore premium fuel is required, not recommended.

Edit:
Page 423 goes on to say that "using unleaded gasoline with an octane number or rating lower than the level previously stated will cause persistent heavy knocking," which validates my interpretation as being correct.

[Allch Chcar]

That's about as clear as muddy water.

Thankfully there is also this.

2013 FR-S Product Technical Info and Specs (from Las Vegas press event)

I skimmed it without thinking about it and if you check the recommended fuel it says premium fuel required.

Any other questions?

[easybreazy]

I've seen this debate many times on the Prelude forums since the engines are mostly high compression engines 10:1 ratio's. Since the FRS/BRZ has a 12.5:1 ratio, which is very high, I wouldn't mess with the higher octane recommendation just to save a few bucks. Do you really want to rely on retarding the timings especially at high rpm's? Do you really want to wait until your engine knocks before switching to premium fuel? It may be called a knock but do you know what it's actually doing inside your engine? A knock is an early explosion inside your cylinders before the piston has reached it's peak (on it's way up on the compression cycle) because the fuel was ignited too early, either due to the lower octane fuel, higher temperatures, old engine, air fuel mixture, etc.. Just imagine your piston having to fight that explosion as it's trying to go back upstream like a spawning salmon. Maybe some people think a car is like a pet, it will get used to eating the cheaper food and some days they'll splurge, haha.

http://www.caranddriver.com/features/regular-or-premium

[chulooz]

Originally Posted by Allch Chcar

That's about as clear as muddy water.

Thankfully there is also this.

2013 FR-S Product Technical Info and Specs (from Las Vegas press event)

I skimmed it without thinking about it and if you check the recommended fuel it says premium fuel required.

Any other questions?

The offical word from the manufacturer makes it crystal clear, its just dont.

Besides arguing for a point that even you wont be willing to support is almost like trolling...

[Allch Chcar]

Originally Posted by chulooz

The offical word from the manufacturer makes it crystal clear, its just dont.

Besides arguing for a point that even you wont be willing to support is almost like trolling...

The manual doesn't say premium required clearly, so I am just complaining at this point.

[azian_advanced]

it would be a good idea to keep a couple of bottles of octane booster in the trunk just in case you end up at a place without 91+ octane. some small towns don't offer anything higher than 87. 87 octane + highway driving (high rpm) = bad.

[michaelahess]

Octane is not a "grade" of gas, that's a misnomer, the gas is all the same "quality". What a higher octane rating does is limit pre-detonation, which is much more important the higher your compression is.

Basically as the piston compresses the gas, the heat caused from this compression will cause a low octane fuel to ignite before the piston hits apogee or top dead center (is that the correct term?) which causes the piston to slam down before it's supposed to, this causes the knock or ping.

Higher octane makes the gas harder to ignite, which allows the higher compression engines to wait till TDC before the spark ignites it vs the pressure.

The ECU will retard timing if it senses knock but it can only do so much. Running 85 on a car tuned for 91 will be bad as the ECU can't alter it enough to prevent this. Undue stress on the pistons and other internals will then shorten the life of the engine.

Now the reverse is also something to take into consideration. Most family vehicles are built to run on 85-89. Buying 91 or higher is just throwing money away, there is literally no advantage to doing this.

Something else to consider, and I do this with my Hemi, fill up with the proper rated fuel, 91 in my case, and if 89 is all that's available when traveling, don't worry about filling say half full of that. It will dilute the 91 but keep you above 89 for the remainder of the tank. And assuming you fill up when no less than half empty, the next time you get 91...things start to even out.

I would much prefer this method over octane boost btw.

[AtlantaRock]

Originally Posted by Allch Chcar

The manual doesn't say premium required clearly, so I am just complaining at this point.

The manual clearly states to use 93 octane and if is not available you can use 91

[Allch Chcar]

Originally Posted by AtlantaRock

The manual clearly states to use 93 octane and if is not available you can use 91

Thank you for pointing that out.

[MTeator]

So it's settled?

[WolfpackS2k]

Where do some of you guys live, 3rd world countries? I've had premium only cars for 13 years straight and I've never had a problem finding a gas station with high octane fuel.

[DeeezNuuuts83]

^ That's what I'm thinking. I don't even know why this was really a discussion topic. It's a 20 cent difference per gallon of fuel, which is less than a 5% increase in fuel costs based on the price of gas today.

[michaelahess]

Originally Posted by WolfpackS2k

Where do some of you guys live, 3rd world countries? I've had premium only cars for 13 years straight and I've never had a problem finding a gas station with high octane fuel.

Wyoming, Montana, even parts of Colorado, higher altitudes more commonly have lower octane fuels. Mind you that's usually only the case at smaller gas stations and towns.