wjburken
Supporting Member
I agree 100%.
When I made the decision to buy a “premium” suv like my Denali’s, I accepted the fact that they may cost a little more to operate and maintain. That being said, to each their own.
5.3 vs 6.2 octane
- Thread starter h2100
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When I made the decision to buy a “premium” suv like my Denali’s, I accepted the fact that they may cost a little more to operate and maintain. That being said, to each their own.
gooffeyguy
Tom
Not all spark knock is audible, and usually already doing some kind of damage by the time it's heard.
Knock sensors are good to have, but they're just basically "listening" for knock then making the ecu retard the timing when it hears it, hopefully in time and not doing any major piston damage.
Best to use the fuel the manufacturer recommends.
Premium 93 octane is currently $1.88 around here. I always use either premium or E85 in my 6.2l
2001 Yukon SLT
2012 Yukon Denali XL
2011 Yukon Denali RIP 5/20/18
Knock sensors are good to have, but they're just basically "listening" for knock then making the ecu retard the timing when it hears it, hopefully in time and not doing any major piston damage.
Best to use the fuel the manufacturer recommends.
Premium 93 octane is currently $1.88 around here. I always use either premium or E85 in my 6.2l
2001 Yukon SLT
2012 Yukon Denali XL
2011 Yukon Denali RIP 5/20/18
donjetman
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I bought a 12 yr old Denali for less than $10k. I wish it had a 4.8L in it for better gas mileage. I have very little need for its 6.2L and hp. I bought it for the AWD, amenities, and its awesome quiet smooth ride. I run mid grade 89 octane in it and get 16.5 mpg. I did run 87 octane until I got a DIC knock sensor message once on one of our road trips. Maybe I'll run premium for the next yr and see what the data says.
donjetman
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gooffeyguy
Tom
That reminds me of my buddy Jon Huber and his '79 mustang 2.9l (2.3 stroked to 178ci running a single PT-74 turbo) 4 cylinder turbo'd motor about 10-15 years ago running 9's (and eventually 8's) and kicking all the v8's asses!
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petethepug
Michael
Wow I like this guy. I've just been acknowledged for using armchair talk and I like it. I did not know they had 85 in Colorado.
donjetman
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It has a lot to do with atmospheric pressure. At sea level the pressure is about 30 inches of mercury or 15 psi. At 10,000 ft, Leadville, CO, its 20 inches of mercury or 10 psi. Lost about 1/3 of the pressure that's being forced into a normally asperated engine, so we lose about 1/3 of our horse power. So my 380hp 6.2L only makes about 250hp at Leadville. Cylinder pressure is reduced as altitude increases, so detonation, pre-ignition, knock is reduced, so the need for higher octane is reduced.
avalonandl
Full Access Member
Swath: There is a Racetrac nearby selling E85 for 1.45 vs. 1.95 for premium at costco -( 2.25 at Racetrac)
Am I better off trying a tank of E85?
swathdiver
Full Access Member
I would! We have E85 for $1.35, my wife apologized for letting the mileage drop and I said who cares, we can fill the whole truck up for less then forty bucks! That last tank delivered about 10.5 MPG and cost just thirteen cents a mile which is this truck's record low. E85 is good for the motor and injectors, cleans them up.
Didn't have enough fuel on board to run down south yesterday so we refilled a little early with E15 on top of the E85 and still averaged 16 MPG @ 75 MPH. That should bust the thirteen cent record nicely!
If you run a couple tanks of E85, it will get up to full strength and the computer will adapt to it, even the transmission.
Leardriver
TYF Newbie
I like Intheburbs answer.
I ran a dyno in Denver at high altitude. Several absolutes were clear.
In a normally aspirated engine, meaning no turbo or supercharging...
Your octane requirements go down about one point for every 1,000 feet above sea level. If you need 91 at SL, 85 runs the same in Denver.
Run the lowest octane fuel that your engine doesn't detonate on if energy and wallet efficiency matters to you. High octane fuel isn't better fuel, it could be argued just the opposite. It has more additives to resist detonation, and it burns slower. Lower octane burns faster and creates more energy IF the engine can peacefully exist, which at high altitude is virtually always. The argument that 85 octane makes more power than 93 is true-ish, but that's an oversimplification. The tradeoff for high octane burning slower than low octane is a tiny bit less explosive power, but you would never feel it.
We had a dirt bike dyno, and would measure bikes with great smelling 104 octane race gas in the CRF450R, and they would make 2 hp less than 91 octane pump gas. I raced MX for 25 years, and always said that if you want to go faster, twist the throttle. Those bikes make more power than mortals can use.
If you are towing a heavy trailer up the mountains, more octane doesn't hurt for that tank as an extra dissipator of heat. The higher altitude of the mountains, and warmer summer air actually reduces your octane requirements even more, but when you are on the gas non stop on long hills, more octane gives you a cheap source of additional margin.
I ran a dyno in Denver at high altitude. Several absolutes were clear.
In a normally aspirated engine, meaning no turbo or supercharging...
Your octane requirements go down about one point for every 1,000 feet above sea level. If you need 91 at SL, 85 runs the same in Denver.
Run the lowest octane fuel that your engine doesn't detonate on if energy and wallet efficiency matters to you. High octane fuel isn't better fuel, it could be argued just the opposite. It has more additives to resist detonation, and it burns slower. Lower octane burns faster and creates more energy IF the engine can peacefully exist, which at high altitude is virtually always. The argument that 85 octane makes more power than 93 is true-ish, but that's an oversimplification. The tradeoff for high octane burning slower than low octane is a tiny bit less explosive power, but you would never feel it.
We had a dirt bike dyno, and would measure bikes with great smelling 104 octane race gas in the CRF450R, and they would make 2 hp less than 91 octane pump gas. I raced MX for 25 years, and always said that if you want to go faster, twist the throttle. Those bikes make more power than mortals can use.
If you are towing a heavy trailer up the mountains, more octane doesn't hurt for that tank as an extra dissipator of heat. The higher altitude of the mountains, and warmer summer air actually reduces your octane requirements even more, but when you are on the gas non stop on long hills, more octane gives you a cheap source of additional margin.
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