I am attempting to help educate some people on the negative sides of using premium gas on a car meant for regular.

I have done research on the API website, as well as the FTC, as well as everything I understand about the way an engine works.

My explination is this: A car that lists 87 octane as the minimum does not benefit from using premium. Higher octane gas takes longer to burn than regular. Using premium on a car designed for regular does this. When the mixture is ignited, by the time the exhaust valves open to scavage the combustion chamber, the mixture has not finished burning through yet (since premium takes longer to burn). This causes a loss of power, can burn the valves, and even get fuel mixture/vapors into your exhaust gasses and into your cat.

Now as for damage, it COULD burn through your valves in the long run, and also cause a faster/greater buildup of crap on your valves, etc. Now this is very long term use of premium where these effects occur. As for short term, since the mixture has not burned completely through by the time it's being removed from the chamber, this causes a slight loss in power as well.


Now from the mechanics I've talked to, research I've done on this site, as well as the FTC and API sites, this is what appears to be the consensus about using premium on a car made for regular.

Some of the arguments I've been facing are that premium has more detergents and cleaners than regular gas. According to the FTC this is not true, since government regulations and rules state that one brand of gas cannot have more/different detergents in their premium gas than what is in their regular. The only change they are allowed to make is addatives to increase the octane rating (which has nothing to do with cleaners and detergents).

From the FTC web site:
The other argument I'm facing is these guys are saying "well i can FEEL a difference and my engine is more responsive and i get better mileage". The only thing I can come up with is change in brand of gas or change in weather/temp/humidity and changes in driving styles/freeway/city driving can cause the better mileage and "more responsive" engine.

It's kinda like bashing my head against a wall, because no matter how much info I offer some of them are simply like "well my stock civic drives better with premium". When really, I know it doesn't.

Any other input or info?

 

I dont know about better or whatever, but my understanding the higher the octane the more cleaning things it has in it...and the less chance of early detonation. Which kindda agrees with what you said. I have ALWAYS used premium gas on any car. I hate being cheap when it comes to cars. I personally had no problem with any damage due to gas or octane ratings, but its very interesting to see someone do that much research and put it in simple terms. Thanks

Hopefully everyone reading this has an S and uses Premium (or better)

I have seen on some shows like "pimp my ride" or whatever where they got a car that requires premium and the owner was putting cheapo gas in it and it completely killed the performance of the car. The did a dyno not knowing it had a tank of crap in it (I think it was an STI) and it did horrible. They later figured it out and took the crap gas out....put in premium....and instant HP and TQ gains.

 

in one of the last threads someone started about using regular in the S, there was a link that lead to a C&D indipendent study of using regular in a premium only car and premium in a regular only car.

Their result was (on a car that required regular) that premium didn't make a difference. However, if the car had a newer ECU with knock sensor, then there was the possibility that the car could benefit. If the car realizes that it's getting premium, it automatically advances the timing giving more power. Again, this was only on certain cars.

Here's the article: http://www.caranddriver.com/article.asp?se...article_id=3604

 

"The results were more dramatic with the test cars that require premium fuel. The turbocharged Saab's sophisticated Trionic engine-control system dialed the power back 9.8 percent on regular gas, and performance dropped 10.1 percent at the track. Burning regular in our BMW M3 diminished track performance by 6.6 percent, but neither the BMW nor the Saab suffered any drivability problems while burning regular unleaded fuel."

Is a quote from that article....thats crazy that the cars designed for premium would really suffer when using only regular gas.

 

I agree that using premium gas is a waste in a non-premium car. However, I have trouble believing that it will damage the car. I don't believe 91 octane burns slower than 87. The flame propagation speed, I believe, is identical. It's the detonation pressure that varies with octane. The higher the octane the higher the pressure/temp it can handle before self-detonating.

I took a combustion class about 10 years ago. l learned some stuff, but it doesn't make me an authority in this subject.

 

There aren't really any negative side effects of using premium in a car that only requires regular, other than on one's pocketbook.

The "slower burning" issue is a red herring. Any kind of gasoline will have completed the burn long before the piston reaches the end of its expansion stroke, let alone beginning the exhaust stroke.

If you read the EPA excerpt more carefully, you'll see that all it says is that the minimum detergent level required by the EPA is the same for all grades of gasoline. Oil companies are free to put more than the minimum in none of their grades, some of their grades, or all of their grades. Typically they will have the same detergent levels in all grades, or more in the higher grades.

That's not the primary benefit of premium for engines with deposits, though. Deposits increase the compression ratio of the engine, meaning that an engine designed for regular may knock unless the spark is retarded. Using premium in this situation will allow the spark to be advanced again, which will result in better performance and better fuel economy.

Bottom line: while using premium in a car designed for regular is unlikely to do too much when the car is new, it may help a lot if the car is 10 years old and has 100,000 miles on it.

 

[QUOTE=Cyclon36,Mar 23 2005, 06:07 PM] in one of the last threads someone started about using regular in the S, there was a link that lead to a C&D indipendent study of using regular in a premium only car and premium in a regular only car.

Their result was (on a car that required regular) that premium didn't make a difference.

 

I would think most people would know that as a given, but I digress.

Putting regular gas in a car that requires premium causes pre-detonation. Bad for the engine, can cause damage, and most certainly a loss of power. Cars that require premium generally have FI or higher compression. Therefore the temperature inside their combustion chamber during the compression stroke is HIGHER. Therefore they NEED the more heat resistant premium gas. If you put regular in, the temperature alone during the compression stroke, can cause the regular gas to ignite/pre-detonate.

 

good point. I never even thought of the carbon buildup raising the compression.

 

Wisconsin man hold up so others can respond too