Racket
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It's science. And history.
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CB750F
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@RANGER PRIDE
LOL, no idea, I've seen no proof, just the internet... lol.
As for your second part, would not be the first time someone sells
snake oil.
dondonbabyraptor
Well-Known Member
Just for your own information. 2017 f150 ecoboost government research. 32.8 mpg on 93 octane, 32.5 mpg on 88 octane on high way conditions. IF cost/mileage is your only concern, get 87oct. Now if you want the extra power then 91+ oct. I don't know all the slight engine differences and if we would get different results but it's worth something at least.
https://www.nhtsa.gov/sites/nhtsa.gov/files/documents/812520.pdf
https://www.nhtsa.gov/sites/nhtsa.gov/files/documents/812520.pdf
VegasRanger
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I’m currently running 91 because of the hot summer months here. The manual recommends 91 during hot temperatures use. As soon as it cools off I’m switching to 87. 91 prices has been killing me.
Motorpsychology
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I get better performance and milage on my Suzuki V Strom (V-twin 650cc) with 91 oct than with 87 oct. The main reason I do is because 91-oct is the only no-ethanol fuel in my area, and my Butt-O-Meter detects an improvement in performance, real or imagined. Besides, I get 60+mpg so the extra ~70¢/gal. doesn't amount to much. In my Ranger, I fill with premium if I will be towing, and/or driving 75-80 in hot weather or hilly terrain.I’m currently running 91 because of the hot summer months here. The manual recommends 91 during hot temperatures use. As soon as it cools off I’m switching to 87. 91 prices has been killing me.
91 octane: 32.8mpg X 18 gallon fill= 590.4 mile range vs 87 octane: 32.5 mpg X 18 gallon fill= 585.0 mile range so it's not worth it to me to run premium all the time in the Ranger.
Fitzmotor
Gold Sponsor
The ECU measures knock and adjusts the timing accordingly, it's the kind you won't really hear, low magnitude.
The ECU does not have a octane sensor input, it is all done with knock feedback, which is VERY different than pre-detonation that you can hear, the best power is right on the edge of knock, it is most efficient at that point as well.
I found that the big difference in mileage and power between fuels is the brand, Chevron is good for both, Shell not so much, cheap 7-11 or off brand fuels feel like 87 octane instead of 91, but here in California we have the some of the worst fuel, full of additives and ethanol, it gets worse when we get the winter blend, mpg will drop 2-3 on that stuff.
The ECU does not have a octane sensor input, it is all done with knock feedback, which is VERY different than pre-detonation that you can hear, the best power is right on the edge of knock, it is most efficient at that point as well.
I found that the big difference in mileage and power between fuels is the brand, Chevron is good for both, Shell not so much, cheap 7-11 or off brand fuels feel like 87 octane instead of 91, but here in California we have the some of the worst fuel, full of additives and ethanol, it gets worse when we get the winter blend, mpg will drop 2-3 on that stuff.
BassRanger
Well-Known Member
This is incorrect. Best power and efficiency is made at maximum brake torque or MBT. Assuming you have enough octane to reach this point, further advancing timing to the point of knock will not gain you anything.
Fitzmotor
Gold Sponsor
I knew somebody would comment on my comment, I should have mentioned at peak torque.
But, when you are on edge of knock AND into knock you can make the most power and economy, once past peak torque you can knock it even harder.
In the Indycar and prototype engines, they would run them into knock which yields peak power, it was down to knock hits per mile, (150-240 mph) at 4-6 knock hits per mile the engine would last, jump to 20-30 knock hits per mile for qualifying or end of race push, it would start to erode away the pistons like a nitrous motor.
The power gains were huge, we would start to reach up to 14+ MPA cylinder pressure, once we figured out how to control the knock with the added power we had to beef up the rod, rod bearing, piston and pin as well as thicker valve heads and chamber casting thickness.
But it was a interesting development, in the beginning the knock would turn into auto ignition, they could not shift the cars as the engine was in glow plug mode and would not shift cut.
So I know the normal thought is knock is bad, but knock and pre-ignition are not the same, most of what a person hears is pre-ignition, a uncontrolled ignition event, knock is different, it occurs at the right time, it's just a violent combustion event due to uneven fuel in the chamber, it would be the intake side of the piston that would start to glow as there is little fuel/space between the intake valves and the piston at full valve lift, so once the valves close that part of the chamber is very lean, that side of the chamber would experience the knock, we could measure the cylinder pressure in different places during testing. Chevy had the advantage on us as their DI injectors pointed at the intake side where ours pointed at the exhaust.
Sorry I got so carried away, flame propagation in a chamber can be interesting but a nightmare too, I should go into GCI where gasoline/ethanol engines run without a spark plug, they light upon knock, probably would have been the latest technology for road cars but EV's are taking over the world anyways.
But, when you are on edge of knock AND into knock you can make the most power and economy, once past peak torque you can knock it even harder.
In the Indycar and prototype engines, they would run them into knock which yields peak power, it was down to knock hits per mile, (150-240 mph) at 4-6 knock hits per mile the engine would last, jump to 20-30 knock hits per mile for qualifying or end of race push, it would start to erode away the pistons like a nitrous motor.
The power gains were huge, we would start to reach up to 14+ MPA cylinder pressure, once we figured out how to control the knock with the added power we had to beef up the rod, rod bearing, piston and pin as well as thicker valve heads and chamber casting thickness.
But it was a interesting development, in the beginning the knock would turn into auto ignition, they could not shift the cars as the engine was in glow plug mode and would not shift cut.
So I know the normal thought is knock is bad, but knock and pre-ignition are not the same, most of what a person hears is pre-ignition, a uncontrolled ignition event, knock is different, it occurs at the right time, it's just a violent combustion event due to uneven fuel in the chamber, it would be the intake side of the piston that would start to glow as there is little fuel/space between the intake valves and the piston at full valve lift, so once the valves close that part of the chamber is very lean, that side of the chamber would experience the knock, we could measure the cylinder pressure in different places during testing. Chevy had the advantage on us as their DI injectors pointed at the intake side where ours pointed at the exhaust.
Sorry I got so carried away, flame propagation in a chamber can be interesting but a nightmare too, I should go into GCI where gasoline/ethanol engines run without a spark plug, they light upon knock, probably would have been the latest technology for road cars but EV's are taking over the world anyways.
Fitzmotor
Gold Sponsor
I got really carried away with that post, sorry.
The point is the mfg can get power gains with increased timing through knock feedback, they have good enough technology and materials to keep it alive closer to the knock edge.
The point is the mfg can get power gains with increased timing through knock feedback, they have good enough technology and materials to keep it alive closer to the knock edge.
- Banned
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I live in Colorado. Your equivalencies are off. Due to altitude (less oxygen less propensity to combust) 85 is equivalent to 87, 87 is equivalent to 89, and 91 is equivalent to 93.
Nobody in their right mind puts premium in their car just for an MPG increase. Especially when prices are this high. Higher octane is for safety and performance.
Higher octane allows for advanced timing without knock or predetonation. If you're tuned, real custom tune not OTS, on premium you should run premium. Even stock Ford's knock sensing system will advance timing.
Also, why did you quote me if "you're not directing this at me."
It IS interesting, and complicated. You should study it some more. It's exactly the opposite of what you think. Turbo = premium.
Edit- this was in response to a post by @FordFreak
Must've got deleted or something.
Last edited:
Gsxrdoug
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What was the question?
FordFreak
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Mid-grade is fine for a little turbo like these. Noticeable difference in my blown Mustang (with a "real custom tune") though. I'd quoted you because I didn't feel like scrolling to the end of the thread to make a post. I deleted my post so you could feel superior about my equivalencies of octane being wrong though. It used to be right until they phased out MTBE in 2003. Everything else you wrote was what I said. You just used different words. Congratulations!
