Quote:
Originally Posted by knowitman
However it is not that simple. Different grades of fuel have nothing to do with the quality of fuel. It is purely a rating of how easily the fuel will detonate based on a laboratory analysis using various tests. Higher octane ratings simply mean that the gasoline and air mixture can be under more pressure and at a higher temperature before the mixture detonates. In fact, 93 octane gasoline has a lower energy content than 87 octane fuel.
Most cars on the road are designed for 87 octane fuel. This means that during normal operation of those vehicles, the temperature and pressure in the cylinder do not get hot enough for 87 octane fuel to detonate. Running 93 octane fuel will not give any benefit in these motors because 87 octane fuel is sufficient for optimal timing in the motor.
Most types of sports cars have higher compression motors. Running a higher compression ratio allows for a car to operate more efficiently on a thermodynamic basis. When comparing two engines that are identical in everything except for the compression ratio, the engine with the higher compression ratio will have more horsepower and fuel efficiency. However, this engine might require a higher octane fuel than the lower compression motor because a higher compression ratio creates more heat and pressure in the combustion chamber. Most cars are built around 87 octane because the increase in power isn't as important and the increase in efficiency isn't enough to justify requiring more expensive fuel.
Cars that have turbos or superchargers generally require higher octane fuels because the act of forcing more air in the combustion chamber means that more pressure and heat is generated during the compression stroke when compared to a naturally aspirated motor. This is also why most turbo or supercharged cars run low compression ratios. The ZL1's LSA engine has a 9.1:1 compression but still requires 91+ octane fuel because the supercharger compressing the air creates the extra heat and pressure.
While turbocharged and supercharged cars tend to require a higher octane rating for the compression ratio of their engine, Direct Injected cars, such as the V6 Camaro, can run a lower octane fuel for the same compression ratio. In a traditional motor, the air and fuel are mixed before the mixture enters the cylinder during the intake stroke. Thus, both the air and fuel and compressed during the compression stroke. As the mixture is compressed it also gets hotter and will eventually detonate. In a direct injection motor only the air enters the cylinder during the intake stroke. The fuel is then added during the compression stroke. This means that the fuel has less time to heat up during the compression stroke and is less likely to detonate. Adding the fuel during the compression stroke also has another benefit. When the fuel is injected into the hot combustion air it wants to evaporate. This latent heat of vaporization then cools both the fuel and air because the fuel is pulling heat out of the air in order to vaporize.
I'm trying to not debate whether or not higher octane fuel benefits the V6 motor in this post. I am just trying to state that octane rating is not a "quality" rating of fuel. It is just the quantification of a particular property of the fuel.
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damn good post and thread , So I got to ask you since you own a Zl1 and have no bias in this I am assuming , If you owned a 2010 LT what gas would you use ? Say you wanted a little more acceleration ,,I always use top-teir 89 , they do not have 93 top tier ,but do have 91 ?