Anyone use 93 octane (premium) fuel on the 3.5?

[AntDeek]

I'm extremely interested in the info about the Coyote and Cyclone (3.5/3.7 Ti-VCT) and its technology to compensate for 93 octane fuel. Anyone have more info?

[TheWizard]

Basically, the engine control computer (PCM, ECM, or whatever it's called in each model) advances ignition timing until the knock sensors show a pre-ignition condition and then back the timing out to a safe level. Since the sole purpose of added octane is to reduce knock, using higher octane fuel in these cars will result in improved performance because the ignition timing can advance a little further with higher octane than with lower octane. Advancing the ignition timing can only produce a limited amount of performance increase before reaching a point of diminishing returns which varies for each design. For example, the Coyote 5.0 in its original configuration went from 402 HP to 412 HP between 87 octane and 93 octane - a gain of just under 2.5% and that's peak horsepower at high RPM. Larger performance gains require more air (and hence more fuel) or increased compression. That's why larger displacement or forced induction are the most common power improvements used.

[AntDeek]

Thanks man great write up! Very interesting!

[omar302]

For example, the Coyote 5.0 in its original configuration went from 402 HP to 412 HP between 87 octane and 93 octane - a gain of just under 2.5% and that's peak horsepower at high RPM.

What about non peak gains? You know, the same that is advertised by tuners. Like at 2000 RPM, if torque was ~200lb-ft using 87 would the gain still be ~2.5%? Or different?

In my MKX, with the 3.7, I feel a noticeable difference in throttle tip in on the highway between 87 & 91.

[Xephiron]

When I bought the car it had 87 octane in it from the dealer, and I used 87 for the 1st tank or 2. I was averaging 18.5 mpg with my normal commute and driving style. I switched to 93 octane and, all else the same, I am showing 19.5-19.7 mpg now and I can "feel" a better throttle response. I can't say it is faster, necessarily, but definitely more responsive (so probably more power). I have a 2017 Sport so 2.7TT

 

Seems like I remember "premium gas is preferred, but 87 will work" whether that was the dealer or my owner's manual or what, I don't remember honestly. I personally do feel like higher octane is better since it apparently helps keep the engine cleaner for longevity, more power and gas mileage (I did buy a sport model, just saying), and hey why not save a little gas. I use Shell gasoline. I have not used an injection cleaner yet, as I only have 3900 miles, but I usually use Lucas Injector cleaner with upper cylinder lubricant.

 

Cheers

[TheWizard]

What about non peak gains? You know, the same that is advertised by tuners. Like at 2000 RPM, if torque was ~200lb-ft using 87 would the gain still be ~2.5%? Or different?

In my MKX, with the 3.7, I feel a noticeable difference in throttle tip in on the highway between 87 & 91.

 

Horsepower and torque follow a curve when graphed and will vary from model to model, often even between vehicles of the same model. The link provided by MaX83_ZA in post #14 provides some examples from different vehicles. In some, like the Miata, the increase was fairly constant across the range while in others, like the F150, both torque and horsepower were lower with 93 octane compared to 87 octane at lower RPM but surpassed the lower octane at higher speeds.

 

Generally speaking, advancing the ignition timing will have more performance impact at higher RPM. This is because the air/fuel mixture takes the same amount of time to burn regardless of engine speed so firing the spark plug earlier at higher speed will help with getting the mixture completely burned thus producing the most efficient use of the air/fuel charge.

 

So to answer your question... I can't say. Your engine may be one that benefits across the RPM range or it may not. The only way to tell is to run it on a dyno.

[AntDeek]

So the follow up question is, besides cost, is there any downsides to running 93 octane in the 3.5 TIVCT?

[chefduane]

I don't think there is a downside other than the cost and the fact that it's not needed. You can drink Perrier exclusively all your life and take it camping with you if you want, but it's really not needed, But if it makes YOU feel better, then that's all that counts.

[tamugrad2013]

Just my two cents since my fuel pump was replaced at 30,000 miles I run strictly top tier 87 octane through my car unless there is no alternative (parents small town when I needed gas and the only top tier place debit card machine wasn't working) usually once per year. I also refuse to fill gas at a station if I see the gas truck filling the underground tanks my thinking is that adding fuel to those tanks mixes up all the settled sediments in the tanks and causes a better chance of that sediment going into my tank and those the fuel filter. Just my thought process.

[WWWPerfA_ZN0W]

And a good process it is!

[PrinzII]

Where I am does not have 93 octane. The highest is 91. Considering I run Costco, the sole choices are 87 and 91. I typically run 89 in the Edge but since Costco doesn't have mid-grade, I just run premium since the octane is not much different.