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MidOH

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Just a high quality knock sensor. Not listening for knocking, that's too late, but actually listening to to sound of combustion. Sounds complex, but it's horribly simple.

Sometimes called a pinging sensor. There may be both sensors, or more.
 

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The ECM and engine knock sensors are constantly changing the timing and fuel delivery. My 218cuin V6 makes 340hp on 91oct, maybe 320 on 87oct. It runs fine on either fuel. I use 89 and 91oct most of the time, 87 for long hiway trips, not much difference in mpg.
 

Billiebob

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Octane requirements change with elevation. 87 might be the lowest rating on the coast but there places in Utah, Colorado, Wyoming where regular has an 83 octane rating. Premium is only 89.

Generally speaking a higher compression ratio needs a higher octane rating but If your car does not generate enough compression to NEED premium fuel, it is a complete waste of $$$ to buy premium.
 
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Cort

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I apologise if I started an argument or anything. I was just speaking from my personal experience with my turbo Chevy Sonic and official figures from Mazda about the turbo CX-5. These could just be two outliers


It's mentioned in the second sentence that on regular the CX-5 makes 227hp and 250hp on premium. Probably, like you said, using and octane sensor to adjust boost, fuel, timing, etc. I'm not sure what method they use

Again sorry if I caused an argument

No argument brother! You are dead on with the turbos. The car is designed with performance in mind and will detune when it reads knock. These are outliers for sure. My twin turbo eco boost does the same thing.
 
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Cort

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I got 35hp on the dyno. Albeit, dyno's are for drive-ability and engine tuning, not hp measuring. (aside from more = better)

Over 400hp from a 6.2l Ford. It really depends on the engines state of tune and sensitivity to the sound of combustion. Obviously a bigger truck engine is going to be tuned conservatively when it senses 87, so it doesn't eat the pistons. Chassis cab trucks get knocked down even further due to most likely harder use.
And where that hp showed up in the rpm range in conjunction with the torque. And were you tuning the ecm or was it a completely stock engine?
 

Cort

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Just a high quality knock sensor. Not listening for knocking, that's too late, but actually listening to to sound of combustion. Sounds complex, but it's horribly simple.

Sometimes called a pinging sensor. There may be both sensors, or more.
If those are Dyno numbers that engine has some mods on it.
 

MidOH

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Mild tune. Dyno accounts for driveline losses.
 

K. Rut

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Realistically just run what you feel comfortable paying for as long as the owners manual says its alright. I know with Chevys (We have a 2010 suburban) they like to live on the knock sensors and have a completely different timing and spark tune for different grades of fuel (we can also run e85). I can run all day on 87 with no worries. Also, for the cost of a cup of coffee when I fill up, I can run 92 and get slightly better power and fuel economy. Is it enough for me to actually notice, nope, will it help my motor run longer if it never knocks... Most likely... Do what you feel comfortable with and don't give it to much thought. Just my .02
 

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As what has been stated, what is your engine tuned for. My wife's 2016 Camaro isn't happy with regular if you drive hard. My 04 TJ didn't care one way or the other. I did notice a difference towing my trailer up long grades but, It was slight.
My 96 cruiser is a different story. Going to my sisters house several times a year. 260 miles one way. With regular I would have to top off. Figure 2.5 tank's round trip. With premium, only bought from Shell, I get there with a couple gallons left in the tank. If the Cruiser even thinks it may detonate, it rips the timing back. When I do the math, it actually cost's me more money to drive to her house if I use regular.
I have a new 2019 Tacoma. I'm waiting until I get 2500 miles on it before I start tracking mileage. So far, it doesn't seem to care.
In my area, I've done mileage tests with almost all the fuel stations in my area. Shell gets me the best but, that can change if I go out of state.
What is the real MPG difference with the 96 80 series? I’m getting right about 12 mpg burning regular- your math seems to equal 16 or 17 mpg in order to break even. Do the math for us please.
 
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smritte

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Your spot on. I get 15-17.
I started around 12(ish). The better fuel netted me some. The biggest was the part time kit then the new motor. When I built the motor, I bumped the compression a little.
Unless I'm mistaken, your actually familiar with my area. If not, I'll give you some map points if you care.
I live in Ontario and my sister lives in Summerland in Vegas. My mileage testing is the drive back and forth. Regular fuel, pre mod's, I had to top off in Baker or I would hit empty by state line. Premium from Shell I got to her house with just enough to fill up before I left for home. Part time got me there with just under 1/4 tank and new motor gets me there with almost 1/3 tank left.
Ive done this same route for 6 years. 2 years on the part time and 2 trips with the new motor.
35's, stock gears, 2" OME and I average 70 mph. I just lifted it 2 more inch's and I'm dying to see how much difference it makes.
 
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chuckoverland

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Realistically just run what you feel comfortable paying for as long as the owners manual says its alright. I know with Chevys (We have a 2010 suburban) they like to live on the knock sensors and have a completely different timing and spark tune for different grades of fuel (we can also run e85). I can run all day on 87 with no worries. Also, for the cost of a cup of coffee when I fill up, I can run 92 and get slightly better power and fuel economy. Is it enough for me to actually notice, nope, will it help my motor run longer if it never knocks... Most likely... Do what you feel comfortable with and don't give it to much thought. Just my .02
Our friend that told us about using supreme lives in Hermiston :)
 
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Lindenwood

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On engines with ECUs programmed to compensate for octane, there can be actual performance benefits.

However, please don't confuse high octane fuel with "high quality" fuel. High octane fuel does not inherently have more additives in it than lower octane fuel. Conversely, high quality fuels have the same cleaning and stability additives regardless of octane.
 
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MOAK

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Your spot on. I get 15-17.
I started around 12(ish). The better fuel netted me some. The biggest was the part time kit then the new motor. When I built the motor, I bumped the compression a little.
Unless I'm mistaken, your actually familiar with my area. If not, I'll give you some map points if you care.
I live in Ontario and my sister lives in Summerland in Vegas. My mileage testing is the drive back and forth. Regular fuel, pre mod's, I had to top off in Baker or I would hit empty by state line. Premium from Shell I got to her house with just enough to fill up before I left for home. Part time got me there with just under 1/4 tank and new motor gets me there with almost 1/3 tank left.
Ive done this same route for 6 years. 2 years on the part time and 2 trips with the new motor.
35's, stock gears, 2" OME and I average 70 mph. I just lifted it 2 more inch's and I'm dying to see how much difference it makes.
I’m gonna give this a try.. I know that non ethanol fuel gets roughly 2 more MPG, but you can’t get pure gasoline just anywhere..
 

Lindenwood

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I’m gonna give this a try.. I know that non ethanol fuel gets roughly 2 more MPG, but you can’t get pure gasoline just anywhere..
My best friend is a petroleum engineer (I was the physics guy). We went through the math calculating energy density of pure gasoline vs ethanol. It turns out the amount you lose in fuel efficiency from using ethanol blends--because it has less energy per gallon, so you have to use more of it for the engine to do the same work--is almost directly proportional to the price difference. Funny how capitalism works :P .
 
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The higher the cylinder pressures the higher the octane and quality of fuel needs to be. Engines with turbo, supercharger, high compression, or aggressive timing curves or tables will likely require top tier higher octane. A standard mild compression engine with a factory timing curve will see no benefit from higher octane fuel. It will benefit from the additives and quality of a top tier fuel. If I put 87 or 89 octane (even the top tier fuels) it will barley make it up a small hill without detonation. But it's higher compression and a pretty aggressive timing curve. So with it I'm stuck with 91 octane minimum at my home elevation. Non ethanol fuels will generally get better mileage. You will only benefit from premium if you engine or tuning require it.
 

Lanlubber

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So we are curious. A friend of ours who visited recently told us we should be using premium gas in our rigs (18 tacoma and 18 crosstrek). He says to use premium regardless of factory reccomendation.
What are you guys thoughts?
Factory spec's are the only way to go. If factory spec's say use only premium fuel, they mean just that. My problem is that my station sells three grades of gas, Regular unleaded (86 or 87 octane) Premium unleaded (88 or 89 octane) and Premium (91 octane). There is a 30 cent / gal difference between regular and premium unleaded, and another 10-12 cent diff between P. unleaded and Premium. I use the 88-89 octane because I feel like I have done what the mfg told me to use (a premium fuel) . I have used the reg grade gas on occasions and see no difference in mileage between reg and premium grade gas. With my final gear ratio of 3.80, I get only 13 mpg, loaded or unloaded at 75 mpg. I get better gas mileage at 60 mph but I never checked to see how much better because I haven't driven that speed for a long enough distance. I have a Land Rover Discovery 2 with a 4.0 engine and it weighs 4576 pounds without gas. It holds 26 gallons @ 8# per gal =208# (+-). To me the logic of premium fuel would have a lot to do with vehicle weight v engine size. My LRD2 is heavy with a small displacement engine so even if the factory didn't tell me to use premium I would. Low compression engines (below 9 to 1) commonly use unleaded regular, Engines with 9-10 to 1 commonly use 88 octane gas and engines with 10 to 1 compression or higher commonly use Premium 91+ octane. That would be my rule of thumb !
Lanlubber
 

Lanlubber

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Sounds like a waste of money to me. I would be more concerned with running 100% gas than the ethanol but then again my Jeep is older than most vehicles here that are now designed to run off ethanol. I have never run premium, even my wife 2019 Buick Encore runs 87 octane and gets 30mpg.
Just curious Jon, is your jeep a 6 cyl or V8 ? I have never heard of a 6 cyl ever needing anything other than regular unleaded gas unless the compression was raised to 10 to 1 or higher and have a hi performance cam.
Lanlubber