Felixldang

Hello guys

just curious if your car is only recommended unleaded 87 gas.. Does pouring premium gas make a different if it's not required?

I've been hearing mix things about this, cause I know the new Es take 87 unleaded. But I have a friend that saying you should pour premium anyways cause it helps keep the engine running longer and have better performance?

Is this true or can you just put unleaded if that what the car is recommended.. I usually just go by what the gas cap says

geko29

The idea that premium gasoline intrinsically creates more power or is categorically "better" for all engines is a very common misconception. This is because most people are unaware that the purpose of Octane is to PREVENT combustion. Therefore, in any given situation, higher octane gas will burn more slowly and produce less peak force against the piston.

The reason many cars, particularly high-performance ones, specify high octane fuel is because they run at high temperatures and/or high cylinder pressures, which can cause pre-ignition. This is where the fuel ignites BEFORE the sparkplug fires. In extreme cases--called detonation--the fuel explodes during the compression stroke and actually resists the intended motion of the piston, which can cause serious engine damage. To protect against these conditions, cars have knock sensors that will retard timing and/or cut engine fueling when pre-ignition is detected. This results in substantially lower performance.

Higher-octane fuel, being more difficult to ignite, is less susceptible to pre-ignition/detonation, and therefore allows these engines to perform up to their potential. However, in cars that specify 87, the only likely outcomes from using 93 is a slight reduction in power output and fuel economy. There are certainly situations in which it could be beneficial--driving up the mountains in 117F temperatures with the A/C on full blast and/or pulling a trailer, for example--but 99% of the time, it's both a waste of money AND counterproductive.

bitkahuna

iTrader: (20)

^^ great post.

Infra

iTrader: (1)

Octane rating has nothing to do with how fast a fuel burns - that's a myth. It is a scale to represent the auto-ignition temperature of a fuel, just like Celsius or Fahrenheit are scales to represent the average kinetic energy of molecules (temperature). As Celsius uses the freezing and boiling point of water as it's standards, and Fahrenheit uses the coldest mixture of salt-water a dude could make and what he thought represented the average human core body temperature as its standards, the Octane scale (RON or MON) uses the auto-ignition temperature of n-heptane and isooctane as its scale.

All that means, is that octane rating is a number relative to a pure mixture of isooctane. To provide more detail than that, we'd have to get into isomers, which I don't want to do. Let's just keep it at this level : different blends of hydrocarbon chains autoignite at different temperatures, and the higher the octane rating, the higher the temperature.

geko29 did a good job in paragraph 2, so I won't reiterate that. But paragraph 3 is incorrect again. Different octane ratings have nothing to do with energy density, just as they have nothing to do with how fast fuel burns. The whole reason higher octane fuel will not increase the power your engine generates is due to the fact that the energy density does not materially change between octane ratings. Engines that require higher octane fuel simply operate more efficiently, as in they extract a higher percent of the energy contained in the fuel. The efficiency of an engine burning gasoline is directly related to the compression ratio, and higher octane fuel allows an increase of the compression ratio before autoignition of the fuel.

*edit* Let me add that this "slow burning" myth is based upon people lighting fuel and watching it. Let's not forget that the environment inside your engine is nothing like atmospheric conditions, so we should not expect the fuel to behave in the same manner.

Different blends of fuels can have different energy densities. Summer/Winter blends, for example, have the same octane rating, but very different energy densities. mmarshall has an annual posting about this. =)

bitkahuna

iTrader: (20)

another great post.

Toys4RJill

For some Toyotas/Lexus models yes, premium fuel will provide more power.

The ES350 in 2007 made more power with premium than the 2012 ES350 with regular.

The Tundra/Sequoia also ran higher horses with the 4.7 during the last generation.

tex2670

Bottom line, beyond the technical reasons, if you have a modern car, and higher octane is not "required" or "recommended", it will provide no benefit for you.

FrankReynoldsCPA

In fact, the manual for my 2012 Fusion specifically said NOT to use higher than 87 octane gas. I know of a few people that have started running 91 though because they claim it alleviates a shifting issue some Fusions have been known to have. I think it's a placebo affect myself.

On my 92 LS400, I noticed absolutely ZERO difference between running regular and premium fuels.

Felixldang

Wowww great post guys.. I like how techical you guys get. It makes the argument soo much better when I explain it to them cause they are sooo close minded

Tks again for all your replies ����

mcomer

Adding to the "old husband tales" that swirled around the subject historically, premium priced fuels used to have more/better additives and the regular stuff had less. You might run a tank of "hi-test" through a car that
did not otherwise deserve it and the extra elements would clean away a bit of the crud and clutter. Thus was born the urban (and rural!) myth of treating your car to the occasional tank of Ethyl.

Toys4RJill

That is not exactly true, but sort of true. Some cars, especially Toyota and Lexus cars were designed to run at certain spec on regular and a certain spec on premium.

mmarshall

It used to be that premium gas, especially from major-brand fuels, had more of the company's detergent-additive blended into it (Chevron's Techroline, Shell's V-Power, etc...) then their regular 87-octane blends to help keep the fuel system and injector-nozzles clean, spark plugs from fouling, and carbon from building up at various places inside the engine. If you filled up with premium when the car only needed regular, the engine didn't necessarily have any more power or fuel-economy, but it would stay cleaner from having more detergents blended into the fuel.

That isn't the case as much anymore. Most national name-brand fuels now put enough detergent into even their regular 87-octane grades that the engine stays adequately clean...especially if you dump a can of BG-44K cleaner into the tank every 30,000 miles or so, which most shops do at major services. (BG products are generally not available in regular stores). In general, Chevron and Shell still are considered to have the best detergent packages, but pretty much any major-brand fuel should keep the engine reasonably clean.

However, there may or may not be good detergents in cut-rate brands....or, for that matter, any detergent at all. IMO using those brands, at best, is a crap shoot.....you're rolling the dice. That is why I strongly recommend (as I have for years, for you who follow my posts) using major-brand fuel. I myself use Chevron or Shell exclusively. Smiling Sam's Discount Gas-N-Go, down the street, may save you a little in the short run, but, in the long run, you will get what you pay for.


And...for those of you who live in the Washington, D.C. area or other areas in the Mid-Atlantic where Giant Supermarkets are available, shopping at them will earn you Shell gas points. Every 100 points you earn shopping with your Giant Bonus Card will save you 10 cents a gallon at any Shell station in the area. I, of course, have a Bonus Card myself, and do a lot of shopping there.

tex2670

LOVE the Giant Gas Stations here in the Philly area. Most off for me so far is $1.30/gal.

FrankReynoldsCPA

That's true. I just remembered that Ford gives different hp ratings for the 5.0 Mustang based on octane.

Sent from my Nexus 4 using IB AutoGroup

chikoo

goes back to HP vs Torque.

A higher octane fuel enables the engine to spin to a higher rpm without misfiring (ie igniting on its own before the spark plug fires). This will result theoretically in higher HP. Now if your car is not misfiring and spin easily upto the limit, I suspect you will discover any gains.