Power and efficiency difference with lower octane levels?

[skinnyb]

I have never even considered running anything less in my Mach 1 than 93, especially now that I have an aftermarket tune, but my F150 that had a Gen 3 Coyote ran like absolute dog crap on 87. It pinged and knocked like an old tractor, I know the computer does its best to retard the timing and make up for it, but it can only do so much with a 12:1 compression engine. I absolutely loved my F150, put 100k miles on it in 4 years that I had it, but I did get a bit tired of putting higher priced fuel in it to run up and down the highway, which I did a lot of. I just knew the sounds it made when running 87 octane, it wasn't happy so I didn't push it. Did Ford say it was OK, yes they did, did I like it, no I did not... Now that said, if 87 was only available where I was filling up and I had to do it to get to a more reasonably priced station, yes I would, but not on the regular for sure.

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[sk47]

Can you tell me what engine are those numbers from?

Hello; The engine is a blueprint engines crate motor. An LSIII. 6.2 liter. 10.7 to 1 compression. I suggest two things. First if you can find the ENGINE MASTERS episode, watch it. I gave only a summary of the overall results. There is more information. The episode is season 6 episode 2.

Second unless some particular additive is put into pump gas the energy is the same regardless of the octane . ENGINE MASTERS did another episode testing if compression makes power. The episode is from season 6 and is episode 11.

The GEN 3 Coyote is a mix of old school mechanical compression and modern tech. In the past it is my take an engine with it's compression ratio would not live very long on 87 octane fuel. The way such an engine has a chance to live is due to the sensors, the direct injection, the computer controlled timing and likely other nannies. A gallon of 87 octane fuel has the same energy content as a gallon of 93 octane fuel.
In a lower compression engine more typical in grocery getter cars there is absolutely no advantage from running higher octane fuel. That engine will not knock on 87. The Coyote has a fairly high compression ratio and can take advantage of that higher compression to squeeze the air +fuel mixture that much more tightly.
My take is the tighter the air+fuel can be squeezed into a smaller space allows for a more energetic pop when the spark plug ignites the mixture. The octane additive helps prevent the fuel +air mix from exploding early simply from the compression. I guess a bit about diesel might be helpful.

Diesel engines have much higher compression ratios that gas engines. The diesel squeezes the air+fuel so tightly into a small space that the heat from the compression alone ignites the fuel. If you happen to have a shop air compressor or even a small one, do this.
Touch the compressor tank before it is turned on. It will be cool. Let it run up to 120 psi, and it will be hot. The why it gets hot is a key. I have 220 shop compressor with a 30-gallon tank. The air in the room can be at 75 degrees F at near 14 psi. By the time my compressor builds up to 120 psi it has squeezed the room air into a space at least 8 times smaller. Not only has the air been squeezed into the compressor tank but also all the 75-degree heat. There are physics lab demonstrations done with piston in cylinders that measure this phenomenon.

My take being that to run 87 in a Coyote some driver considerations ought to be made. Do not lug it around in 5th or 6th gear. Especially in a manual do not try to accelerate from 30 mph while in 6th gear. Keep the revs up a bit. Be careful in extra hot weather and when the car is carrying a heavy load. Be careful at higher altitudes. Be careful when pulling a trailer.
(Note -Last week i got behind a Mustang pulling a trailer. Had drag slicks, fuel cans and a tool box on the small trailer. )Might be a good practice to run the higher octane fuel under such conditions.

 

[Garfy]

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It will run fine on 87 with the Ford stock tune. Mine before I added the Ford performance kit, ran just fine. The only time you may have an issue is at high elevation. Then you may need to run 91.

I don't think it would be a problem at higher elevations as that condition results in less oxygen due to lower atmospheric pressure which probably explains why areas like UT, CO, etc. only have gasoline at 85 and 91 octane instead of 87 and 93 like you do at sea level locations. As for spark knock, I don't think anyone here has heard it from their engines as the PCM will detect the onset of detonation from the knock sensors long before it is even audible to our ears.

 

[EFI]

The results
87 octane = 498.9 lb/feet torque(T) @ 5200 RPM / 539.4 HP @ 6400 RPM/ AV T 475.5 AV HP 452.7
91 octane = 501.1 lb/feet torque(T) @ 5300 RPM / 539.6 HP @ 6400 RPM/ AV T 476.3 AV HP 453.6
110 octane = 499.1 lb/feet torque(T) @ 5300 RPM / 539.9 HP @ 6400 RPM/ AV T 475.1 AV HP 452.5
116 octane = 497.4 lb/feet torque(T) @ 5300 RPM / 541.3 HP @ 6400 RPM/ AV T 474.7 AV HP 452.1
A one and a half HP spread. Not much

There is no way in hell that 116 octane made 2 more hp and less torque than 87 octane on any generation Coyote.

E85 is only ~108 octane and makes massive amounts of power over 93, even more so over 87. And the vast majority of the power from E85 is due to the increase of ignition timing not the cooling affect of the ethanol.

 

[NightmareMoon]

Ethanol content maters probably more than octane rating for gas mileage. Someone could do the math on E10, E15 etc. Ethanol is less energy dense than gasoline, and the computer will adjust to burn more of it, and that means lower MPG.

if its 93 octane, but they're getting that octane with corn juice, the mpg will drop. So in a situation like that, 89 or 91 or whatever that is pure gas will give you better mileage. It may also cost more than stations selling E10 or whatever.

Anyway, I always ran 93 in my GT, and the current tune is a 93 tune, so that's what I run unless I'm going cross country and I can't find any. Its rare up here in Wisconsin and costs $4, but it exists.

 

[sk47]

There is no way in hell that 116 octane made 2 more hp and less torque than 87 octane on any generation Coyote.

E85 is only ~108 octane and makes massive amounts of power over 93, even more so over 87. And the vast majority of the power from E85 is due to the increase of ignition timing not the cooling affect of the ethanol.

Hello; Bear in mind the EM episode did not use a coyote engine. It was an LS 6.2. I do not recall if it had a carb but think perhaps it did. Also pretty sure it did not have the computer nannies. Also keep in mind the post was to illustrate the basic fact that the energy (power content) exists only in the gasoline itself, not in the octane additives.

It is my take that E85, a mix of 85% alcohol + 15% gasoline has two qualities. It resists detonation (knock) and the alcohol has extra oxygen.

One of the reasons I appreciate ENGINE MASTERS is they do the basic fact checking. I knew already from making lesson plans for physical science classes that a gallon of gasoline holds the same energy content regardless of octane additives. The EM program is a handy way to show this.

Again, watch the EM episode about does compression make power. That may answer the questions.

 

[MAGS1]

Anyway, I always ran 93 in my GT, and the current tune is a 93 tune, so that's what I run unless I'm going cross country and I can't find any. Its rare up here in Wisconsin and costs $4, but it exists.

If you’re close to IL, cross the border to get 93 if you can’t find it in Wisco. We only have 93 for premium here

 

[sk47]

I don't think it would be a problem at higher elevations

Hello; Fair enough. I do not know what mechanism would cause knock more at high altitudes. Afraid I repeated something from a previous members post without actually understanding the why. It seemed prudent to include such as a precaution. Might be better to run some 93 in the high mountains than to learn the hard way.
I apologize for the lapse.

 

[sk47]

Hello; What would be useful could be videos similar to ENGINE MASTERS which use the Coyote engine. I searched briefly a while back and found some dyno runs. A thing is such dyno runs do not compare parameters in the same way.
I know some of you are much better at finding stuff on the web.

 

[Paddles]

 

[Garfy]

Hello; Fair enough. I do not know what mechanism would cause knock more at high altitudes. Afraid I repeated something from a previous members post without actually understanding the why. It seemed prudent to include such as a precaution. Might be better to run some 93 in the high mountains than to learn the hard way.
I apologize for the lapse.

Yes, I wish we had 93 whether we needed it or not at 5,000 feet. I was just surprised to see each grade of gasoline having 2 octane points less than what I was accustomed to at my old residence which was within a couple hundred feet of sea level. I did notice a drop off in acceleration here though it's not as bad as back in the days of carbureted engines. I had a '78 302-2v which dramatically fell off at altitude; I recall it barely having power at 10,025 feet as I floored it and it bogged and felt like the exhaust was restricted.

 

[S550HPP]

I have never used below 93 on the Mustang even when the mustang was stock. moto it's fine maybe not ideal. Lots of here about it. But lots of friends and co-workers with Coyote F-150s use whatever gas is cheapest and seem to have no issues.

My bronco on the other hand the power difference is very noticable and very really and annoyed the shit out of me

I run 93 in my Bronco 2.7 all the time and did it in my HPP as well.

It doesn't cost that much extra per tank or per mile.

 

[sk47]

I run 93 in my Bronco 2.7 all the time and did it in my HPP as well.

It doesn't cost that much extra per tank or per mile.

Hello; Around me the options are 87,89 &91. There is a 70 cents per gallon increase from 87 to 91. Thats $7.00 per every ten gallons. With the lower MPG of a Coyote such will add up. I suppose much depends on how well off a person happens to be. Or perhaps, like myself, the ingrained idea of wasting money without a sound reason.
The Coyote presents a conundrum somewhat different from many engines. The Ford engineers offer a full factory warranty which allows the running of 87 octane. Such being the case the situation devolves into a sort of how you feel about it answer.
I have two stories. First is about my mother who insisted on running 91 in her early 90's Pontiac sedan with the legendary 3.8 V6. An engine needing only 87 octane. Never was able to convince her such was a waste of money. The upside being the 91 octane did not put the engine at risk, just used up extra money.
The other story is about a 1989 F-150 pickup I owned. Had the 300 six. Was rated to use 87. However, as the years piled up, I could note some pinging when pulling a load. I began running 91 in one tank and 87 in the other. Using the 91 with a load.

Then there are those who get "tuned" for 91 or 93. I do not know the details of how that works. I suspect the computer nannies are changed so the timing does not retard so much. Maybe work the air-fuel mixture thru the RPM range. That is for others.

The more substantial question is can a person run a stock engine with a factory tune on 87 without damage to the engine? I want to think so. I get why others do not.

 

[Backkick]

Octane rating is its resistance to preignition. The higher the number the more additive is added. They all start out as the same fuel. The reason the higher octane makes more power is that the engine timing is advanced. With today's knock sensors the PCM monitors the sound of the engine listening for detonation. It will retard the timing until it no longer knocks. Conversely, it will advance timing to just before it knocks. All of course within a set range. When a car is tuned the range of the ignition timing is advanced to run on the higher octane beyond the factory limits. But now you can no longer downgrade the fuel since the knock sensor will not be able to adjust the timing lower than what the tuner has set. Now with some premium fuels, they also add a bunch of other additives to help keep the valves clean. These additives along with the octane booster, displace the amount of fuel you get, so 1 gal of 87 will actually have more BTUs in it than 1 gal of 93. Granted it's a small fraction but worth noting since it will affect gas mileage per tank full. What Engine Masters, great show by the way, sometimes tell you, and sometimes they don't mention, is when they run these tests, Steve Burle` or Steve Dulcicich will tweak the ignition timing and carburetor for optimal performance. They edit out the number of tuning dyno pulls to only show the final result. So the results sk47 listed should have included the number of degrees of timing added to arrive at those power numbers.

Just curious: It is true that the octane rating is an indication of its resistance to preignition, but I have been told that extra additives are not the only way to increase the octane rating. Gasoline is actually a mix of liquid hydrocarbons of diverses octanes rating, some with a higher rating, some with a lower rating, the final result being an average of all these substances. So, to increase the octane rating, it is apparantly possible to further refine (by fractional distillation) the gasoline to remove more of the lower octane rating hydrocarbons, thus increasing the final average octane rating. So the higher the final octane rating value, the less there are lower rating liquids, That is why a higher octane rating fuel costs more, it talkes more time and effort to refine the fuel to the desired rating by removing the unwanted substances. Of cours there are additives, but more often than not they have nothing to do with the octane rating. Rather, these additive are there to insure cleaner combustion to better comply with the existing emissions standards. Thoughts are welcome.

 

[mmff88gt]

Hello; Fair enough. I do not know what mechanism would cause knock more at high altitudes. Afraid I repeated something from a previous members post without actually understanding the why. It seemed prudent to include such as a precaution. Might be better to run some 93 in the high mountains than to learn the hard way.
I apologize for the lapse.

I am a self-admitted barbarian. I wash my car using only one bucket, etc. I have 70K miles on my 2019 GT and have only run premium in it for a couple of tankfuls while at high altitudes on a Route 66 trip. I always try to do a couple of pulls to redline in 2nd and 3rd on a weekly basis to "blow the carbon out." My engine shows no ill effects from a steady diet of regular gas. I typically am using "top tier" gas which has a better detergent package, but no higher octane.

Also: https://www.caranddriver.com/features/a28565486/honda-cr-v-vs-bmw-m5-ford-f-150-dodge-charger/

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