What's up with midgrade gas?

Sunoco
By Sunoco Fuels
Feb 20, 2024 | Sunoco, Sponsored Content, fuel, gas, gasoline, Sunoco Race Fuels, Midgrade | Posted in News and Notes | From the June 2023 issue | Never miss an article

Photography Credit: Chris Tropea

If performance cars get premium gasoline and standard cars get regular fuel, why does midgrade exist? Because some situations call for fuel with octane between, depending on region of the country, 87 and 90.

Before grabbing that nozzle, Zachary J. Santner, senior specialist of quality at Sunoco, advises you to consult the owner’s manual. It will explain your vehicle’s exact octane requirements. As he reminds us, octane isn’t a unit related to power potential; it’s the measurement of a fuel’s resistance to knock. 

In the U.S, the big number on the pump displays the Anti-Knock Index rating: the average of the Research Octane Number and the Motor Octane Number. Why does this matter? Just be aware that different countries use different rating systems, with Europe putting more emphasis on the RON. (If you have a U.S.-spec car, the owner’s manual will speak to you in U.S.-spec units.)

If the owner’s manual says to feed the engine regular fuel, Santner continues, then any extra octane won’t deliver any more power. The engine simply isn’t configured to take advantage of that extra knock resistance. (This is assuming, of course, that the engine hasn’t been modified and is in a proper state of tune.)

If the owner’s manual says to run premium, will midgrade help save a few bucks? It might, Santner says, noting that many modern engines will retune to accommodate the lower octane. 

The latest Mazda MX-5, for example, delivers peak performance when fed 91-octane fuel. “Regular unleaded fuel with an octane rating from 87 to 90 (91 to 95 RON) can be used,” the owner’s manual states, “but this will reduce performance slightly, such as reduced engine output, and engine knocking.”

Can you mix in midgrade as necessary to either add some octane to regular or save money as needed? Yes, Santner says. In fact, your local station likely only has two tanks for unleaded fuel: regular and then premium. The two products are blended at the pump via a simple 1:1 ratio to create the midgrade product.

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Comments
kb58
kb58 UltraDork
5/25/23 2:34 p.m.

On the Mazda CX-30 turbo, 87-91 octane can be run and the knock sensor figures it out. Somewhat surprisingly, it affects hp more than torque, where hp drops from 250 to 227, but torque only drops from 320 ft-lb to 310.

Sure, it's not exactly a hot hatch for the track, but the point is that newer engines do indeed cope with varying grades.

obsolete
obsolete GRM+ Memberand Dork
5/25/23 2:50 p.m.

Yeah, but which midgrade?

 

I saw this while passing through Kansas on a trip a few years ago (as you may have guessed by the price). I'm sure this is just a fancy blender pump that can mix different ratios of 87 and 91, but who needs 3 midgrades, with 1-point resolution? It amused me enough to take the picture.

kb58
kb58 UltraDork
5/25/23 2:59 p.m.

On top of that, temperature and altitude play a huge part.

z31maniac
z31maniac MegaDork
5/25/23 3:37 p.m.

In reply to obsolete :

Yep, the mid-grade is blended. When I worked at QT years ago, most stores had 4 tanks under the parking lot. 2 of 87, 1 of 91, 1 of diesel. 89 was a blend of 87 and 91. 

frenchyd
frenchyd MegaDork
5/25/23 3:55 p.m.
obsolete said:

Yeah, but which midgrade?

 

I saw this while passing through Kansas on a trip a few years ago (as you may have guessed by the price). I'm sure this is just a fancy blender pump that can mix different ratios of 87 and 91, but who needs 3 midgrades, with 1-point resolution? It amused me enough to take the picture.

It selects different ethanol levels. 
     Added ethanol will help your engine run cooler. At a slight increase in fuel consumption.  Yes it also increases horsepower if your cars capable of dealing with it.  Does your car have the flex fuel emblem on the back?  If so it will automatically adjust timing and mixture strength. 

jmabarone
jmabarone Reader
5/25/23 3:57 p.m.
z31maniac said:

In reply to obsolete :

Yep, the mid-grade is blended. When I worked at QT years ago, most stores had 4 tanks under the parking lot. 2 of 87, 1 of 91, 1 of diesel. 89 was a blend of 87 and 91. 

I was at a Sheetz last month and saw basically the same thing posted for the tanker drivers.  One 30k gal 87 tank, one 10k gal 87 tank, one 10k gal 93 tank, and a 10k gal diesel tank.  Three grades (plus diesel) at the pumps so either they mix it when it is going in or they just mix at the pump between the high and low to make the mid.

buzzboy
buzzboy SuperDork
5/25/23 4:13 p.m.

A few years back my island(and other parts of eastern NC) had a regular unleaded shortage. People didn't want to pay for premium so they were buying mid-grade. Being that mid-grade is a blend it was taking ages to pump out. Glad I own a bicycle

obsolete
obsolete GRM+ Memberand Dork
5/25/23 4:50 p.m.

In reply to frenchyd :

There are ethanol blender pumps, but that's not what this is. The pump in the picture is only blending gasoline (<=10% ethanol).

jimbbski
jimbbski SuperDork
5/25/23 5:42 p.m.

Where I live buying "mid-grade" gasoline is a waste of money.  You can get 93 octane or 87 octane. To get 89 which is what mid-grade is around here you don't get a 50//50 mixture of 87 & 93 but something like  60/40 to get 89 but you pay more for it as the price is halfway between 87 & 93.  If I'm looking for something more than 87 I prefer to blend it myself by just buying the amount of each grade to get what I want. 

 

FYI: I can remember the days when there was only a 10 cent difference between each grade. Now it's something like 45-50 cents.  

Peabody
Peabody MegaDork
5/25/23 6:31 p.m.

My truck is tuned for 91, and on 87 there's a huge drop off in power. But 89 seems to satisfy the knock sensors, and saves me some bucks over 91

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