What a difference 91 octane makes in the 2.0 motor.

[Mark S.]

My sense is that while premium might make a slight difference in normal driving, it isn't huge. It's not like there's a 50-75 hp difference between 87 octane and 91/93.

Someone in the Mustang EcoBoost community did dyno testing between regular and premium fuel. With premium the engine produced the advertised 310 hp. With regular is was 275, which is a bit more than a 10% reduction. I think it's logical to assume numbers for the 2.0L would be similar. The advertised max with premium is 250 hp, so with regular you can expect around 225.

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[Mark S.]

Found this interesting...

The gist of his post is that premium fuel provides better performance than regular, which we already know because that's what the owner's manual tells us. I question much of his commentary on safety however. He seems to be using the terms "preignition" and "detonation" interchangeably, but these are completely different phenomenon.

Preignition occurs when the fuel/air mixture ignites in the cylinder PRIOR to the spark plug firing. This can occur due to a hot spot inside the cylinder, residual heat from the previous combustion event, etc. An engine that experiences preignition for any appreciable time is unlikely to survive the event.

Detonation, on the other hand, is the uncontrolled ignition of the mixture AFTER the spark plug fires. The heat and pressure generated by the flame front causes the mixture to combust in other areas of the cylinder, generating a second (or third) flame front. When the two flame fronts collide you get a ping or knock.

Here's the critical difference between preignition and detonation: Our engines are designed to avoid preignition. Everything from the engine control system, heat extraction systems, oil specification, etc. is expressly designed to prevent preignition, because it will destroy the engine. Detonation, on the other hand, is NECESSARY to engine operation. The powertrain control module manages engine control parameters to PURPOSELY induce detonation--albeit light detonation for very brief periods. The PCM does this to establish safe operating limits. Power output is ramped up until the PCM detects detonation (via knock sensors on the engine), then it dials back power output to safe levels. This allows the engine to safely produce maximum power based on the current conditions. And this occurs whether you use regular or premium.

The bottom line is that our engines will occasionally experience detonation because they have to for the PCM to get the most power out of them--that's the way they are designed.

 

[sajohnson]

The gist of his post is that premium fuel provides better performance than regular, which we already know because that's what the owner's manual tells us. I question much of his commentary on safety however. He seems to be using the terms "preignition" and "detonation" interchangeably, but these are completely different phenomenon.

Preignition occurs when the fuel/air mixture ignites in the cylinder PRIOR to the spark plug firing. This can occur due to a hot spot inside the cylinder, residual heat from the previous combustion event, etc. An engine that experiences preignition for any appreciable time is unlikely to survive the event.

Detonation, on the other hand, is the uncontrolled ignition of the mixture AFTER the spark plug fires. The heat and pressure generated by the flame front causes the mixture to combust in other areas of the cylinder, generating a second (or third) flame front. When the two flame fronts collide you get a ping or knock.

Here's the critical difference between preignition and detonation: Our engines are designed to avoid preignition. Everything from the engine control system, heat extraction systems, oil specification, etc. is expressly designed to prevent preignition, because it will destroy the engine. Detonation, on the other hand, is NECESSARY to engine operation. The powertrain control module manages engine control parameters to PURPOSELY induce detonation--albeit light detonation for very brief periods. The PCM does this to establish safe operating limits. Power output is ramped up until the PCM detects detonation (via knock sensors on the engine), then it dials back power output to safe levels. This allows the engine to safely produce maximum power based on the current conditions. And this occurs whether you use regular or premium.

The bottom line is that our engines will occasionally experience detonation because they have to for the PCM to get the most power out of them--that's the way they are designed.

Excellent explanation Mark.

 

[sajohnson]

Someone in the Mustang EcoBoost community did dyno testing between regular and premium fuel. With premium the engine produced the advertised 310 hp. With regular is was 275, which is a bit more than a 10% reduction. I think it's logical to assume numbers for the 2.0L would be similar. The advertised max with premium is 250 hp, so with regular you can expect around 225.

As I was typing that post I recalled that you had mentioned something about the Mustang being dyno tested with premium and regular, but could not remember the numbers. A 10% difference sounds about right. I would not expect much more than that.

IIRC, I mentioned this before, but I have a 2002 WRX modified to Cobb Stage 2. It can be programmed for any octane fuel. Before looking into it, I figured there must be a significant difference between 87 and 93 octane. In reality (according to Cobb) there is only a +5 hp difference, and zero (0) increase in torque! If anything, Cobb should be incentivized to "embellish" the numbers, not minimize them. Needless to say, that's a different situation than a BS, but there are some parallels (turbocharged 2.0L, but the WRX compression ratio is lower).

Just something to consider:
https://www.roadandtrack.com/car-culture/a13043642/why-you-shouldnt-trust-dyno-numbers/

The "Engineering Explained" video linked to in the above R&T article:


I'm not sure how much the above might have effected the Mustang measurements (if at all). Most "don't trust dyno numbers" articles and videos refer to comparing results from *different* dynos -- which makes complete sense -- not the same dyno.

However, even with the same car (his S2000) on the same dyno with back-to-back runs, the measured torque varied from ~125 to ~144 lb-ft. -- see about 1:35 in the video.

 

[Mark S.]

However, even with the same car (his S2000) on the same dyno with back-to-back runs, the measured torque varied from ~125 to ~144 lb-ft. -- see about 1:35 in the video.

Yes, there's variation. You have to do several runs and average.

 

[SgtT11B]

From my own car, the Mustang. Just going from 91-93 octane raised horsepower by 5. I never bothered to check with 87 octane, because the car has a Ford Racing Powerkit and 91 is the minimum.

My point of the video is that even though the BS can run on 87 octane, its best in my opinion to run the better octane. They just run better all around. Its a turbocharged engine with a still relatively high compression ratio for a forced induction vehicle. Normally with forced inductin you start to see compression ratios fall under 9:1, this car still has a 10:1 for the 2.0 and 11:1 for the 1.5L. In fact the 1.5L will benefit more from the higher octane than the 2.0L due to its compression ratio.

 

[SgtT11B]

Someone in the Mustang EcoBoost community did dyno testing between regular and premium fuel. With premium the engine produced the advertised 310 hp. With regular is was 275, which is a bit more than a 10% reduction. I think it's logical to assume numbers for the 2.0L would be similar. The advertised max with premium is 250 hp, so with regular you can expect around 225.

Correct, this just backs up what Ford said. That 87 octane would be about 10% less power but the same amount of torque.

 

[wiyeti]

Great thread, learning a ton. What effect does ethanol content have? I am always putting 91 octane in my tank, and Kwik Trips in Wisconsin have ethanol free. Many gas stations have ethanol free "recreational" fuel. Curious what the difference is with and without the ethanol. Thanks.

 

[sajohnson]

From my own car, the Mustang. Just going from 91-93 octane raised horsepower by 5. I never bothered to check with 87 octane, because the car has a Ford Racing Powerkit and 91 is the minimum.

My point of the video is that even though the BS can run on 87 octane, its best in my opinion to run the better octane. They just run better all around. Its a turbocharged engine with a still relatively high compression ratio for a forced induction vehicle. Normally with forced inductin you start to see compression ratios fall under 9:1, this car still has a 10:1 for the 2.0 and 11:1 for the 1.5L. In fact the 1.5L will benefit more from the higher octane than the 2.0L due to its compression ratio.

Good point. My 2002 WRX engine has an 8:1 compression ratio, which is (or was) more typical for engines with relatively high boost pressure.

10:1, and esp 11:1 was unheard of for forced induction. In fact, 11:1 was considered high for a naturally aspirated engine.

 

[sajohnson]

Correct, this just backs up what Ford said. That 87 octane would be about 10% less power but the same amount of torque.

I didn't realize Ford had issued a statement on it -- good to know, thanks.

 

[SgtT11B]

Great thread, learning a ton. What effect does ethanol content have? I am always putting 91 octane in my tank, and Kwik Trips in Wisconsin have ethanol free. Many gas stations have ethanol free "recreational" fuel. Curious what the difference is with and without the ethanol. Thanks.

To be frank I would take 10% ethanol 91 octane over 0 ethanol. Especially in a forced induction car. It also helps in cooling the intake charge.

 

[SgtT11B]

I didn't realize Ford had issued a statement on it -- good to know, thanks.

They did on the Ecoboost Mustang when it came out. As the fuel and timing maps allow the higher torque output but starts cutting timing at the higher rpm levels. Hence the drop in power but still makes the same torque. There is a ton of torque management with these vehicles.

 

[69cuda340s]

Good point. My 2002 WRX engine has an 8:1 compression ratio, which is (or was) more typical for engines with relatively high boost pressure.

10:1, and esp 11:1 was unheard of for forced induction. In fact, 11:1 was considered high for a naturally aspirated engine.

My '16 F150 3.5 ecoboost is around 10:1 compression. Some ppl on F150 forums swapped to lower compression pistons which reduces detonation and allows ecu to dial in more timing boost. Ppl reporting significant power increases with the piston swaps. So the higher compression might be for emissions cause it definately not for performance.

 

[sajohnson]

My '16 F150 3.5 ecoboost is around 10:1 compression. Some ppl on F150 forums swapped to lower compression pistons which reduces detonation and allows ecu to dial in more timing boost. Ppl reporting significant power increases with the piston swaps. So the higher compression might be for emissions cause it definately not for performance.

VERY interesting, thanks!

 

[Mark S.]

My '16 F150 3.5 ecoboost is around 10:1 compression. Some ppl on F150 forums swapped to lower compression pistons which reduces detonation and allows ecu to dial in more timing boost. Ppl reporting significant power increases with the piston swaps. So the higher compression might be for emissions cause it definately not for performance.

It's for efficiency. Higher compression ratio yields better fuel economy.

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