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'14 Mustang GT - Downgrading from 93 to 87 octane

5K views 11 replies 12 participants last post by  OX1 
#1 ·
Good evening,

I've been putting 93 octane into my Mustang since late 2013 - is it okay to make the switch to 87 octane now? I know the car can run fine on 87 octane, minus losing around 20 hp - but with me running on 93 for so long should there be issues?

The reason I would be downgrading is I just got a new job that requires me to drive around 120 miles a day, meaning I'll have to fill my tank at least twice a week. That extra .60 per gallon is going to start adding up quick.

Thanks in advance!
 
#2 ·
If you have the factory tune installed, you should be fine.
 
#3 ·
From what I've read, the fuel economy with 93 is better than 87 so you might not be saving much money. Is 91 available near you? If so, it'l be cheaper than 93 and the car will run fine. Does the job pay enough to cover the $18/week difference? If so, stick with 91+. Otherwise, do you have a more fuel efficient car to drive instead? Does any of that driving count as company expense? If so, the'll pay you a mileage stipend or you can deduct on taxes.
 
#4 ·
I don't have a 2013 Mustang, I have a 2016 GT. I don't drive in severe duty situations so I mostly use 87 octane.



Check your owners manual on recommended fuel. It should be listed in the Fuel and Refueling section about fuel quality.



In the 2016 owners manual the 2.3L, 3.7L and 5.0L engines the fuel recommended in the owners manual is 87 octane. The only exception listed is severe duty usage such as towing a trailer is when you use premium.



"2.3L EcoBoost and 5.0L V8 Engines
We recommend regular unleaded gasoline
with a pump (R+M)/2 octane rating of 87.
Some stations offer fuels posted as regular
with an octane rating below 87, particularly
in high altitude areas. We do not
recommend fuels with an octane rating
below 87.
To provide improved performance, we
recommend premium fuel for severe duty
usage, such as trailer tow."


"3.7L V6 Engines
We recommend regular unleaded gasoline
with a pump (R+M)/2 octane rating of 87.
Some stations offer fuels posted as regular
with an octane rating below 87, particularly
in high altitude areas. We do not
recommend fuels with an octane rating
below 87."



If the owners manual for 2013 says the same thing, then using premium if it is not a severe duty situation for increased performance, then it would be a waste of money.



I only used premium on one occasion. It was when the pumps at the local Costco for regular would not pump, but the premium would still pump. Because of the pump problem they sold premium for the same price as the regular. I put in 3/4 of a tank of premium with the regular already in the tank. I noticed no change in fuel economy on my trip home on the freeway, from any other time I drove the car home on the freeway with regular alone.
 
#5 ·
I'm pretty sure you don't get any real HP gains just from switching to a higher octane fuel. Your car only sees HP gains if you have a specific tune for that octane rating. Correct me if I'm wrong.
 
#6 ·
The ECU in the 2010 and later cars WILL produce more power on the higher octane fuel, because it automatically adjusts the spark timing (and maybe other things?) to take advantage of the higher octane. So it's sort of like it "self tunes" for the higher octane (or lower). Custom aftermarket tunes can push it a bit farther by taking away some of the safety factor that is built in to the factory tune.

Back to the OP -- as long as you have the factory tune, not a custom or aftermarket tune that was written specifically for 93 octane, you should be fine.

You might have a little knocking as the car adjusts for the lower octane, but the knock sensor is very sensitive and I bet you won't even notice it, and I'm pretty sure it will happen very quickly. I'd just go a bit easy for a while after making the switch; and don't create an conditions that lead to knocking, like lugging the engine in too high a gear or immediate full throttle and high RPM.

I will be amazed if you can tell the difference in performance in street driving.
 
#7 ·
had the same issue with my job, I got a passat TDI since my car was already paid off.

But yeah the the mpg difference wasn’t much of a difference. You might save a few bucks. My main concern was the added wear and tear my car since it already has 80k on her...


Sent from my iPhone using Tapatalk
 
#8 ·
I've seen a youtube video comparing 87 octane vs 93 octane gas on a 2011 v6 Mustang. The dyno showed 6 or 7 wheel horsepower more using 93 octane. I've read the 5.0 makes 12 extra wheel horsepower using 93 octane.

My Mom's 2010 Taurus with a 3.5 v6 says in the owners manual, for extra performance use premium gas. Ford considers 91 octane gas as premium...………...
 
#10 ·
As long as you have a bone stock 13 GT you are fine to swap to 87 from 93 octane. If you plan to do any modifications, 87 octane will not be ok.

I'm pretty sure you don't get any real HP gains just from switching to a higher octane fuel. Your car only sees HP gains if you have a specific tune for that octane rating. Correct me if I'm wrong.
Not the end all authority, but from my own experience and what I have seen, there is a difference between 87 and 93 octane. I saw slightly better MPG's and better midrange power. Max vs max hp there isn't that much of a difference, but in the mid range there is more of a sizeable difference between 87 and 93 octane. On something like an 11 gt https://www.mustang6g.com/forums/threads/87oct-vs-93oct-dyno-sheet.82583/ with the only difference being gas.
 
#12 ·
When stock, I noticed zero SOP difference on my 14, 5.0 auto from 87 or 93.
 
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