This is especially important for people that drive cars with high-compression engines, like some BMWs. Putting low octane fuel in a car with a high-compression engine could cause the engine to knock or ping, which could cause major damage if it goes on for a long time.
Filling up your BMW, or any other car, with premium gas can hurt your wallet. Depending on your BMW model, you can technically save money by using regular fuel, but it will come at a cost. Most modern BMWs can run on regular gas, thanks to more electronic components, but this can place stress on parts including electronic knock sensors in your engine.
You can think of this EcoBoost engine's more aggressive high-octane tune as a sort-of sport mode that can be switched on or off with every fill of its We always assumed that mid-grade fuel existed chiefly to bilk a few more dimes from the type of people who ask the dealer to undercoat their car. Turns out it's also for owners of Fiat Chrysler's Hemi 5. With no mention of that on the fuel-filler door, though, a driver would have to read the manual to know. With just miles on the odometer and looking as if it had already been hand washed with grit sandpaper a half-dozen times, this Charger is unlikely to ever taste 93 octane again.
Oh well. The Charger's manual says 87 octane will provide "satisfactory fuel economy and performance. Similar to the BMW, the Dodge's gains on the dyno 14 horsepower and 23 lb-ft of torque translated into negligible improvement in our real-world acceleration testing. Saddled with elephantine heft and eager to spin its rear all-season tires at launch, the Charger posted the same 4. At triple-digit speeds, the higher power on 93 octane gave the Charger an advantage measured in tenths of a second.
The Dodge also posted a 0. Just as important, the bellicose roar of the iron-block Hemi and the Charger's ability to reduce its rear tires to jungle-gym ground cover are unaffected by the fuel in the tank. While Ford's EcoBoost F stands out as an obvious exception, the Dodge Charger's numbers make for a tidy summary of our findings. If you buy fuel with an octane rating above the manufacturer's requirement, you're likely to feel it in your wallet more than the seat of your pants.
How your engine constantly invites and silences engine knock to estimate a fuel's octane rating. Your car doesn't know the octane rating of the fuel in its tank. Instead, the engine controller calculates an inferred octane with closed-loop logic that continuously advances the ignition timing until it detects knock, which occurs when a portion of the fuel-air mixture ignites before the spark-plug-initiated flame front reaches it.
The further the computer can advance the timing without provoking knock, the higher the octane rating. During knock, the flame front travels through the combustion chamber up to 10 times quicker than the normal spark-initiated flame front. Left unchecked, these pressure waves can damage the head gasket, pistons, or cylinder head. But the occasional brief knock is a useful tool for checking that the engine is operating efficiently. It's detected with one or more knock sensors bolted to the block to sense the oscillations created by the pressure waves with a typical frequency between 7 and 16 kilohertz.
Fuel prices are always fluctuating and are steadily on the rise. In a tough economic climate, it can be hard to condone spending extra cents on high-performance gasoline. This means that you get more miles to the gallon, because it optimizes engine function, meaning that little fuel is wasted, allowing you to go further on a single tank of gas. When low-quality or sub-par fuel is used, power levels will drop sharply and acceleration will feel weak.
The way engineers help you avoid pings and knocks is by using an octane sensor. The presence of this sensor in most cars built later than means that, if your car was built later than that year, you can run regular fuel without much fear of damage to your engine. The only possible exception would be that under heavy load, for example, and while pulling up a steep hill, you might still experience detonation, but mild detonation is not as detrimental as a full-blown knock.
This is not to say that you get all the benefits of premium fuel while running a lower octane. While any engine might make less power burning low-octane fuel, the effect is magnified in boosted cars and the high-compression engines we mentioned earlier.
So how can you tell if you own a car with a high-compression engine? Generally, BMW M cars fall into one of these two categories. The fabled e39 and e46 cars from the early s each featured
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