Mid Grade

What are the pros of buying mid-grade gas?

Gas stations are starting to only display the first grade gas on their signs and mid-grade is 12 cents more. Why would I as a consumer want to buy that gas?

Short answer at the bottom for people who don’t want to, or don’t understand the rest of the explaination…

OK, so first let’s get this straight… what’s changing in the gas is the octane, not the “quality”. So what is octane or what does it mean… what it translates to is the amount of time the gas takes to burn. This is hard to describe in real life terms because we are talking about something that happens ludicrously fast. But lets slow it down and take a better look.

Your car is designed to have spark happen at a certain time optimized for a certain octane gas and with compression etc all taken into account. So as the piston moves up to the top of the motor on it’s compression stroke the spark goes off at just the right time to ignite the gas and get the biggest explosion to happen at the best time to give your car the most power “bang for the buck” so to speak. The explosion is forcing the piston back down in it’s chamber and that thru gears is what’s moving your car.

So, back to gas. Low octane gas has a much quicker burn rate… it’s explosion is faster. High octane gas has a much longer burn time (by much we’re talking milliseconds if that lol). So then, what to do for your car?

I’ll start by talking about what happens when you put low octane gas into a car designed for high octane gas since we’re all somewhat familiar with this one… it knocks! What is a knock… well, in this case what is happening is that the explosion is so fast that it’s occuring before the piston reaches the top of it’s stroke…. so it’s trying to force the piston back down before it’s reached the top… essentially trying to turn the crankshaft in the opposite direction. Not good.

And then what happens when you buy high octane gas for a car meant to run on low octane? Well, long story short, you’re wasting your money and possibly getting worse gas milage. Why? because instead of the explosion happening at the very best time to force the piston down in the power stroke, it’s burning after the piston is already heading in that direction… thus part of the explosion is being lost and you’re not getting power from it.

If you don’t quite get what I’m saying, or would like to see a pic of how a compression engine works here’s a relatively decent pic I just found thru google: http://www.keveney.com/otto.html The yellow is the explosion of gas… you can see that it starts near the top by the sparkplug… and yet even in this picture it would be hard to see what I’m talking about… still too fast.

OK, I know this is probably beyond what some people want to know or understand. So, long story short… use what your car suggests… or, if you want to be tricky, use whatever makes your car not knock… if it knocks at low octane, go to the middle, etc. But putting high octane in a car that calls for low is wasting your money.

Bootcamp: QA- Describe Low Grade, Mid Grade & High Grade Wee