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Premium Fuel

T

tornadog

Golden Member
My car manual says that only premium fuel(91 Octane Rating) should be used. In our area, there are only 3 choices, 87,89 and 93. Should I just go with the 93? I read on one of the forums where people were filling the tank half with 89 and 93. I thought it was a joke, but they were really being serious about it.
 
Can't go wrong with 93. 87/89 might work depending on your engine tech. Most engines have a knock sensor and will pull back timing in the event of knock.

What kinda car?
 
You can put 89 and be fine. In my Acura 3.5rl, I put 87, even if the manual says 91 premium only. I have been fine driving like this for the last 6k miles.
 
ViviTheMage said:
Minimum for A4 2.0T is 91 as well...I usually put in 93 though, sometimes I see 92, but pretty rare.
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87 oct will work in that engine, you'll lose about 40hp of the 200 it's rated for. 89 oct will be about a 20hp loss, 91 will get you the full 200hp. If you chip the car then going over 91 oct becomes worth it if you have a 93 oct map, usually 240 for those tunes. Putting 93 oct in a stock A4 though is utterly pointless.
 
You could just fill up around half tank and switch between 89 and 91 each fill up. That'll equal out close enough to 91.

If you don't want to just use 93. Biggest loss from 89 is loss of power and your engine may develop a knock.
 
Anyways, I'm running my '06 G35x on 87 for the winter, and might use 93 come spring time again. 89 doesn't make financial sense, and 91 doesn't exist here.
 
89 Will probably be fine as long as it's not super hot outside, and you're not hammering the throttle constantly. If you hear it ping or get a CEL, switch back to 93/91 immediately.
 
91 and up always if the car takes premium. If no 91, use 93, 94, whatever.
I never once ran regular or mid grade in my premium fuel cars, always 91 or higher.
 
Or be a cheap ass, run 87, then complain about the lack of power, pining/clacking sounds.

A riend of mine bought a new Nissan Murano when they came out. Had it for ~3mo, and asked me how to adjust the valves. Turns out he was using 87 the whole time (91+ Manufacturer recommendation) and the clattering from the preignition made him think there was a problem with the valves. He switched to 93, ran like a new car.

There's a REASON they put those minimums, and you sacrifice performance and possibly mileage using anything less.

Is premium really THAT much more expensive?

All of my cars require premium, not worth dicking around with less.
 
Last time I was in the US, buffalo area, there was only a 1 cent difference between 93 and 91 at a Sunoco pump. I stopped pumping 91 and put in 93. You're MDX can probably run on 87 no? My 01 Lexus can but I lose power and a little fuel economy.
 
Why even ask, if the owner's manual specs 91, it means 91 at minimum. 93 is fine.

87 is not, but you may get away with it if the engine has a good knock sensor system. Or you may not.

Why make the computer back off the timing by putting in cheap gas? You'll just have less efficiency.
 
DVad3r said:
Last time I was in the US, buffalo area, there was only a 1 cent difference between 93 and 91 at a Sunoco pump. I stopped pumping 91 and put in 93. You're MDX can probably run on 87 no? My 01 Lexus can but I lose power and a little fuel economy.
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Why would you do that? Higher octane is actually more difficult to get ignited and it's only advantage is that it doesn't spontaneously ignite (knock). It simply has a higher percentage of "octane" to "heptane". Heptane being easier to ignite under pressure, and octane more difficult.

You only lose fuel economy because you aren't running the motor at peak efficiency.

Sunoco and most other gas companies only have 2 tanks in the ground. Regular and Premium. They blend the two to get those 6 different octane selections.
 
bobdole369 said:
Why would you do that? Higher octane is actually more difficult to get ignited and it's only advantage is that it doesn't spontaneously ignite (knock). It simply has a higher percentage of "octane" to "heptane". Heptane being easier to ignite under pressure, and octane more difficult.

You only lose fuel economy because you aren't running the motor at peak efficiency.

Sunoco and most other gas companies only have 2 tanks in the ground. Regular and Premium. They blend the two to get those 6 different octane selections.
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Most modern cars that require premium will advance the timing to take advantage of higher octane fuel. They will also retard the timing to prevent knock if you use lower octane fuels.

Basically, the higher the octane, the higher the hp and the better the efficiency, with modern engines tuned for premium. Within reason, of course. The stock tune will probably not be able to take advantage of race fuels, for example.

So, you will not lose anything by using 93 vs 91 in a modern engine requiring premium fuel, you will gain some hp and some efficiency.
 
When I tell people I have to use 91, most say it would piss them off if they had to do the same with their car.

It costs about 150$ extra per year, who cares. People suck at math... 😀
 
LTC8K6 said:
Most modern cars that require premium will advance the timing to take advantage of higher octane fuel. They will also retard the timing to prevent knock if you use lower octane fuels.

Basically, the higher the octane, the higher the hp and the better the efficiency, with modern engines tuned for premium. Within reason, of course. The stock tune will probably not be able to take advantage of race fuels, for example.

So, you will not lose anything by using 93 vs 91 in a modern engine requiring premium fuel, you will gain some hp and some efficiency.
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Not always true. They will adjust down, but most cars will not adjust to higher octane automatically. Thats what a 93 octane tune (or e85) will do.
 
There is no 93 in my area either. There is 91 or 92 with 10% ethanol. I would love to run 93 in my 2011 WRX. I only use 91 but I knew the car was a high maintenance bitch lol. Premium fuel and synthetic oil only.
 
ExarKun333 said:
Not always true. They will adjust down, but most cars will not adjust to higher octane automatically. Thats what a 93 octane tune (or e85) will do.
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If they adjust, they are usually adjusting by listening for knock. Ergo,they will take advantage of higher octane fuel.

I can't think of a modern car that requires premium that won't take advantage of 93 octane over 91 octane.

A specific aftermarket tune for 93 may do better than the factory tune, though.
 
angry hampster said:
89 Will probably be fine as long as it's not super hot outside, and you're not hammering the throttle constantly. If you hear it ping or get a CEL, switch back to 93/91 immediately.
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It's also affected by air pressure. A fuel that can be added to 10:1 compressed air might work fine up in the mountains. Then you take it down to sea level and it starts knocking. The air at lower altitudes is thicker.


Is premium really THAT much more expensive?
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It's about 10% more expensive where I live. 10% in fuel cost is sometimes enough to make a person choose one car over another. 10% is the fuel difference between the Corolla and the I4 Camry. 10% is enough for people to declare that all Chrysler vehicles get horrible gas mileage (PT Cruiser was about 10% worse than competitors).
 
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