Gasoline question

[Hornin Hong Kong]

Is there any utility gained from buying higher grades of gasoline?

A guy in our natural resources group claims it's a scam and you just get the cheapest gas. He claims the benefit is so minimal that buying the expensive gas is like buying an extended warrantee at best buy or car rental insurance on vacation.

If it matters depnding on car type can you tell me if it would be worth it for:

1) BMW X3 w/v6
2) BMW 525i
3) Aston Martin v12 Vantage

 

[pasotex]

It depends on the compression ratio of your engine. Certain cars do need a higher grade. It should be in the owner's manual. I would be surprised if the BMW's did not require at least an intermediate grade of gasoline. You do not want your engine to ping (which is a sign of predetonation). Most cars can retard the timing to adjust for a lower grade of gasoline, but they can only do it to an extent. My Acura TL requires 91 octane which sucks when prices are high.

 

[Hornin Hong Kong]

Thank you. Read a few articles. Im certainly not feeling any difference in the X3. It seems like you can theoretically lose performance but it's in no way bad for your car - is this a reasonable conclusion?
The Link
The Link

 

[pasotex]

I think it depends on the compression ratio. Generally, I think your conclusion is correct but there are certain cars with high compression ratios that genuinely need a higher octane level.

 

[HornHuskerDad]

I use mid-grade in my 350Z and have not seen any ill effects. If it has affected the power, I can't tell the difference.

HHD

 

[Hornin Hong Kong]

I will try it in the Aston and see if i can tell the difference

 

[accuratehorn]

My understanding is you only need the octane your model calls for. If it says minimum 87 octane, you shouldn't need the 89 or 91 octane gas.
However, if your engine gets carboned up, the deposits take up some room in the combustion chamber area, and you may need a higher grade to keep it from pinging.
However, if a car these days is pinging, most of them have a "knock sensor" which retards the timing to keep it from pinging. So you won't know it is pinging by sound, but you may feel a loss of power if the timing is being retarded by the computer.
Then there is the question of additives. The higher grades of gas may have more and better additives which are good for the engine, but it is hard to determine the truth of this claim, or whether an engine really needs them.
In general, if you put a higher octane gas in an engine than the engine needs, you are just wasting money, as the mixture fires just fine with the gas rated for the car.

 

[Perham1]

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[BadgerinATX]

My background isn't in engines, but I know a little about this. Many BMWs have systems that allow you to safely drive with regular fuels. Whether or not your car has this capability is beyond me. I think it senses the engine knocking and then the system adjusts the ignition timing to prevent future knocking. Because this is an adjustment and not the design intent, the change will likely result in lower power and lower efficiency. Probably not enough efficiency loss to offset whatever gain you get by paying for lower octane fuel.

The car is designed for high octane fuels not so you can look good at the gas station or to make you shell out a quarter more per gallon, but because the engineers are designing a high performance vehicle that needs greater compression. Personally, I wouldn't rely on doing something that the car is not designed to do - especially long term.

Now, if your car cannot compensate for the knocking then I'd really avoid it. What's happening is that pockets of fuel are combusting at times and in locations that are not good and over time are destructive to the engine.

 

[RayDog]

If you try a low grade on a car that specifies a higher grade keep track of your fuel economy. Retarded timing will cost you in efficiency as well as power, especially if you try to make up for the loss of power with the accelerator. The loss in efficiency may eliminate some or most of your expected savings. Worst it may effect engine and engine component and sensor life.

I only use premium in my Aston Martin but it has 4 2-barrel Weber carbs.

 

[Hornin Hong Kong]

I have no problem paying ore if in fact it is good for the car, i just would be horrified if i was getting scammed.

For years i paid for rental car insurance and im still mad about it

 

[ScoPro]

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[accuratehorn]

The owner's manual and a sticker back where the gas cap is located will state the required octane for the car. Use the fuel with this octane, not higher. Use a good brand with good additives like Shell, Chevron, or Texaco (Techron is a good fuel injector cleaning additive).

 

[CottonEyedHorn]

To get the manufacturer's HP and MPG rating, you use the octane they recommend. You lose a little of both if you don't but otherwise there's no harm, unless the hit on MPG outweighs the $$ you saved at the pump.