What is the difference between mid grade and premium gas

Are there any vehicles that require the use of midgrade gasoline? Read on…. You see it every time you pull in to the gas station to fill up.

Situated there, between the regular and premium gasoline options on the fuel pump, is a mysterious third choice: Midgrade. What is midgrade gas? The overwhelming majority of car owners fill their vehicles with regular-grade gasoline. Consumers fortunate enough to drive certain luxury or high-performance models may purchase premium fuel, as its higher octane rating typically is often recommended or required for optimal engine performance in those vehicles. Per one industry estimate, about 85 percent of gasoline sold in the U.

This leads to an obvious question: Why do fuel retailers bother with midgrade? Midgrade fuel began appearing in , as leaded gasoline was being phased out. This, in turn, can lower engine performance and increase emissions. Engines with a high compression ratio typically require higher octane fuel to achieve its intended level of performance, fuel efficiency and emissions.

While you might save money on gas, your car will be less powerful and fuel-efficient. This can make a huge difference in vehicles with available turbocharged engines.

While older vehicles may be susceptible to engine knock when running on low octane fuel, modern ones are equipped with sensors to help prevent knock—and by extension, engine damage.

You might save money on gas, but in this situation, you get what you pay for. Research by AAA found that these vehicles saw a slight increase in performance and fuel economy using premium gas. Depending on what and how you drive, commuters looking to get from Point A to Point B may not notice the difference or care. At the end of the day, it all comes down to your preference. Your car, your rules. Compared with premium fuel, regular feed sapped the F's urgency both leaving the line and in the meat of the tach sweep.

The rush to 60 mph softened to a still-blistering 5. Tapped into the Ford's CAN bus, we recorded a peak boost pressure roughly 1. The high-octane gas also helped when soft-pedaling the accelerator, elevating mph fuel economy from That won't make a financial case for running 93 octane, but then you didn't buy the expensive engine as a rational choice.

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.

Stephen Russ, senior technical leader for gas engines at Ford, says this normal knock is usually detected and addressed within one or two combustion cycles and poses no threat to the engine.

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