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Ford Mustang EcoBoost Loses Big Power on 87 Octane

Ford recommends that the 2.3L EcoBoost 4-cylinder in the 2015 Mustang be run on premium fuel for the best performance, but a new report indicates that the power numbers drop significantly when lower octane gasoline is substituted to save on fuel costs.


Like so many of the big insider topics on the 2015 Ford Mustang, this spicy bit of information comes from the folks at This information isn’t officially from Ford – in fact, Ford reps have refuted the correctness of the information – but it does come from Ford materials that weren’t intended for public consumption.

Reduced Power on 87 Octane
Someone in the community got ahold of a Ford training manual that explains that when the 2015 Mustang EcoBoost is run on 87 octane, the computer adjusts for that reduced fuel quality. When the computer makes those adjustments, it reportedly reduces horsepower from 310 down to 275 while torque drops from 320lb-ft to 300lb-ft. This is a pretty significant decline for something as seemingly minor as lower octane fuel, but it goes to show how important it is to run premium fuel in a performance vehicle. The extra cost is worth the money, especially in the case of the 2015 Mustang.

Those lowered power figures account for an 11% reduction in horsepower and a 6% decline in torque, although it was originally believed that running 87 octane in the 2015 Mustang EcoBoost would reduce power by some 13%. For those who don’t want to do the math, a 13% reduction in power would give the 4-cylinder Mustang around 270 horsepower.

Ford Disputes These Numbers
According to Autoblog, Ford Motor Company reps insist that these numbers are not accurate. The company won’t officially say how much the horsepower drops when you run the 2015 Mustang EcoBoost on 87 octane, but the company insists that torque levels remain unchanged. In other words, perhaps the horsepower numbers in the training manual are correct, but it seems to be all but official that the torque output is still 310lb-ft on the cheaper gas.

2015 Ford Mustang Galleries:
Live images from the 2015 Ford Mustang Detroit Debut
A look at the similarities in styling across the 2015 Ford Mustang trimlines
The 2015 Ford Mustang in Triple Yellow

Based on the lack of comment on the horsepower numbers, perhaps the original estimate of 13% is indeed accurate for the loss on 87 octane and Ford is happy to let us all think that it is only 11%.

Don’t Be Cheap, Feed Your Mustang Premium Fuel
While the 2015 Ford Mustang EcoBoost can be run on 87 octane, owners of the new turbocharged pony should do themselves and their cars a favor and pay the extra 20 cents a gallon for premium fuel. Considering that gas prices are hitting modern lows around the country, there is really no reason that someone who just bought a 2015 Ford Mustang cannot foot the bill for the better gasoline. Not only is it better for your turbocharged engine, but it also allows you to unlock the full potential of your boosted pony car.

Also, now that Ford Performance is rolling out a line of tuners for the 2015 Mustang EcoBoost that will reportedly add a whopping 90lb-ft of torque, owners will have another reason to run premium fuel. Should the Mustang EcoBoost tuner offer the same 90lb-ft increase as the Focus ST, the new pony car would pack a whopping 410lb-ft of torque – but likely only on premium fuel.

Source: via Autoblog


John Goreham    January 6, 2015 - 4:40PM

I am 110% against premium fuel for a number of reasons. Hyundai once released its test numbers for the Genesis when run with premium (91) vs 87. It was a very small difference in power. I'd love to know the fuel economy difference. Where I live we have only three grades at almost all stations. 87, 89, and 93. 93 is WAAAAY more than 87. Not just 20 cents (now) but if regular is 2.29 93 is about 2.89. Back when regular was 3 bucks, premium was 4. My aim would be to make every manufacturer enable the cars to run on full warranty on 87, and publish their numbers on 87, for both fuel economy and power. They could also reveal the numbers on premium. Premium would stop selling that week.

BrainTrust (not verified)    January 7, 2015 - 7:36PM

In reply to by John Goreham

Increased octane does not add power. It only prevents detonation. If your car is built for 87 octane, your performance increase moving to high octane is minimal to none. But, super/turbocharged engines and engines with high compression and/or advanced timing need higher octane to prevent predetonation. Using lower octane causes the computer to make changes like retarding the engine timing and loss of boost and a significant power loss is observed. In other words, if your car is designed for 87 octane, anything higher is a waste of money. If it's designed for high octane, anything less shouldn't ever be considered.

john gorebeef (not verified)    January 7, 2015 - 7:55PM

In reply to by John Goreham

You mention you are 110% against running premium for several reasons, but other than cost you fail to list any. Its not that manufacturers cannot make cars that will run on 87 octane, its that it cannot make 310 HP 4-cylinder engines that will do it. I suggest doing some research on why vehicles require higher octane. And no, its not because uncle Bill puts premium in his Yaris and gets an extra 25 hp. It doesn't work that way. By the way, who is really buying a 4 cylinder mustang anyway? Pulling up beside a GT in a 4-cyl. is like walking up next to a horse at a urinal. Just save up and buy the real car, otherwise get a focus/fiesta that are meant for 4 cylinders.

ryan (not verified)    January 7, 2015 - 8:41PM

In reply to by John Goreham

You kinda have to understand how higher octane gas works to get this but the octane rating has nothing to do with the "power" of the gasoline but rather it's ignition point and burn time. Premium gas does not contain more chemical potential energy than regular gas at all. 93 octane gas actually burns slower and is harder to ignite than 87 octane, hence it's less volatile. Here's a simple explanation of why some cars need premium. You want your engine to ignite the fuel in each cylinder at precisely the right time in the engine cycle otherwise things can go boom and get expensive quick. Cars with a higher compression ratio or forced induction (like this turbocharged mustang) tend to generate higher pressure in their cylinders which makes them more predisposed to premature detonation which could lead to catastrophic engine failure. Modern engine management computers will remedy this by spraying more fuel into the cylinder as this drops the air fuel ratio and lessens the chance of predetonation. For max power your car needs an optimal ratio of air and fuel mixed in the cylinder but like I said the engine management computers in these cars are trying to prevent the thing from blowing up harder than they are trying to make max power. Higher octane gas being less volatile allows the engine to run with a more optimized air fuel ratio and thereby make more power (assuming the ecm is calibrated for premium). In other words, this engine is intended to run premium therefore it can safely make more power on premium. Fill it up with regular and the ecm de-tunes the engine for safety purposes.

Tom Saroch (not verified)    November 21, 2021 - 9:43PM

In reply to by John Goreham

If you don’t understand simply engine engineering you shouldn’t make stupid statements. Your Hyundai really isn’t a fancy vehicle anyway. It’s basically turboyd to give that pos enough power to keep up with its own shadow. So to keep from getting run over spend the few extra pennies at the gas pump or purchase a desent car in the first place. I also doubt that the actual figures were close regardless of fuel used. That’s assuming it was tuned correctly for premium fuel. Also not using a Top Tier premium fuel will create many negative problems down the road for any turbo engine.

Dan (not verified)    January 6, 2015 - 6:24PM

I live in the Washington DC area and even with declining gas prices premium costs about $.60 more than regular. If I could find a $.20 differential, buying premium would be a no-brainer.

Bob (not verified)    October 13, 2016 - 1:49PM

In reply to by Dan (not verified)

Then stop living in DC. That's your problem. If you don't live in expensive places then you don't have to put up with $.60 cents per difference prices in octanes. Nobody held a gun forcing you to live in DC. You chose that on your own free will. That's your own fault. Move to a cheaper state.

James Finlay (not verified)    January 7, 2015 - 4:38AM

Traditionally using lower Octane fuel requires retarding of ignition timing - and thence other actions more than likely. This will result in power loss and also increased fuel consumption ( so think of extra fuel costs for this reason). It can also cause engine to run hotter. All this happens these days in the Engine Management systems and with engines like Ecoboost where high specific power / litre are extracted the effects of lower octane fuel will be even more pronounced than were experienced on old technology engines. Don't forget we have very high cylinder pressures here with Turbos - and protection from detonation is critical as effects of detonation are terminal and expensive.

Alex (not verified)    January 7, 2015 - 9:17AM

John, I don't agree with your opinion... When you have cars with high compression or forced induction, it's safer to run higher octane fuel. They ignite at a much higher temperature which helps to prevent the fuel from igniting before the spark hits it. This is why premium is recommended in high performance cars. Nowadays with more modern cars with advanced sensors, as shown with the Mustang here, they typically can adjust their programming to account for lower octane fuel... with lower performance being the obvious side effect.

dave (not verified)    April 17, 2016 - 7:57PM

What a pointless article. NO. The 2.3l equipped models are not a performance vehicle. If that's what matters to you, get the bigger engine and then sure, run higher than 87 octane, but be real with yourself about whether you are being nice to your vehicle if you're flooring the gas pedal because if you aren't, what do you car if a STREET ride loses a few HP it shouldn't need?

John (not verified)    December 9, 2022 - 5:21PM

#1concern about using cheaper gas in your car should be what build up of carbon deposits are you collecting in your engine components! Spark plugs will suffer, Valves will suffer (they will leak with uneven deposits). All sorts of damage will occur faster with bad deposits! People have to have an EXTENSIVE knowledge of engine engineering, or Take the word of others who do.