I've tried to explain that to people and it's no use.
Also the fact that here in Denver 85 is the same as 87 at sea level.
Tried to explain that if the vehicle calls for 87 in the owners manual that it's the same as 85 here,again waste of time.
Cheap alternative to premium?
- Thread starter AJB0009
- Start date
Also the fact that here in Denver 85 is the same as 87 at sea level.
Tried to explain that if the vehicle calls for 87 in the owners manual that it's the same as 85 here,again waste of time.
My problem with going up hills too slow is that for a given gear, the torque curve really does matter. In my previous car I found I had to keep it in 2nd unless I got up to maybe 30 MPH up a specific hill, when it would be fine in 3rd. But if I let it drop in speed/revs, the engine would noticeably lug.
EVs are way different. No gears and the torque is completely flat for maybe 40-50 MPH. They're almost perfect for climbing hills. They should have no issues climbing up a steep hill at 2 MPH. I'm not sure I could do that in my car, even in 1st all the way.
To some degree, maybe, but not when there's forced induction. With a turbo the boost pressure is usually the limit. Turbos were developed for aircraft engines in order to overcome thinner air.
And a lot of carmakers don't approve the use of lower than 87 AKI at all any more, regardless of altitude. I had a look at the one for my wife's Civic, and that's actually 86, but no mention of altitude. The other thing at high altitude is that if it's OK, it just won't destroy the engine, but in general naturally aspirated engines lose power. With forced induction, it still loses power, but not as much since the maximum boost pressure will be the same. This suggests that for specialty racing applications (like the Pikes Peak Hill Climb), an ECU can be programmed to increase boost with higher elevation. Not sure how that works though.
Turbocharging At Elevation
A naturally aspirated combustion engine will lose 3% of its power for every 1,000 ft of elevation gain. Add a Garrett turbocharger to minimize the loss
www.garrettmotion.com
For what it's worth, Lucas Fuel Treatment and Upper Cylinder Lubricant says on the bottle it reduces the need for higher octane fuel.
I used it in a 2003 V6 Maxima which called for premium without issues.
I used it in a 2003 V6 Maxima which called for premium without issues.
If you actually NEED 93 octane, you have a "trusted station" and you don't care what the cost is.
This cat doesn't need Premium octane
Straight snake oil...but Forest has always been a good businessman
Zee09
$200 Site Donor 2023
I need 91 but here very few selling anything but 87/89/93 as the norm.
And the cost difference between 91 and 93 is nil.
They do? Somewhere else besides in the PDS?
And did your 2003 V6 Maxima have issues before (such as pinging) that the additive corrected?
Not exactly. I remember Red Line used to say SI-1 could reduce the need for high octane fuel. However, they were referring to older cars with carbon deposits that led to preignition. Cleaning off the deposits doesn't boost octane, but reduces any need to go with higher octane rating fuel to compensate.
Correct. If anything it very slightly reduces the octane rating of the fuel.
I too cannot see what premium gas has anything to do with downshifting!!!
It's all rolling resistance. I find if I overinflate my tires by at least 20 lb. There is less tire actually touching the pavement so I have less resistance ,it's kind of like trying to steer a old covered wagon but mpgs go way up . I also have some Doge Coin to sell for 1 dollar.
My hybrid ran just fine using 85 aki in Utah. If I drove back to CA with 85 aki in the tank, the knock sensors will tell the ECU to retard the timing to compensate until I get a full tank of 87 aki again.To some degree, maybe, but not when there's forced induction. With a turbo the boost pressure is usually the limit. Turbos were developed for aircraft engines in order to overcome thinner air.
And a lot of carmakers don't approve the use of lower than 87 AKI at all any more, regardless of altitude. I had a look at the one for my wife's Civic, and that's actually 86, but no mention of altitude. The other thing at high altitude is that if it's OK, it just won't destroy the engine, but in general naturally aspirated engines lose power. With forced induction, it still loses power, but not as much since the maximum boost pressure will be the same. This suggests that for specialty racing applications (like the Pikes Peak Hill Climb), an ECU can be programmed to increase boost with higher elevation. Not sure how that works though.
Turbocharging At Elevation
A naturally aspirated combustion engine will lose 3% of its power for every 1,000 ft of elevation gain. Add a Garrett turbocharger to minimize the loss
Car makers makes the assumption for most of the population, and most of the population don't live in the Rocky mountain states.
If you increase the boost above of where the turbo is efficient, it does the job but the heat increase is a lot higher than running in its sweet spot, so you will need the higher AKI to prevent pre-ignition.
The piece I linked from Garrett is really about a specialty application where they're dealing with really thin air. I guess in that application, the ECU is linked to an altimeter to increase the boost at higher altitudes to make up for the reduced air.
I was under the impression that most turbos are physically capable of considerably higher boost than their typical settings, and that the boost is limited because they might damage the engine with too much. But at higher and higher altitude, that would only be compensating. They have a chart that shows how the boost is adjusted at sea level vs 10,000 ft to roughly produce the same power.
Turbo science is a little more complicated than that.The piece I linked from Garrett is really about a specialty application where they're dealing with really thin air. I guess in that application, the ECU is linked to an altimeter to increase the boost at higher altitudes to make up for the reduced air.
I was under the impression that most turbos are physically capable of considerably higher boost than their typical settings, and that the boost is limited because they might damage the engine with too much. But at higher and higher altitude, that would only be compensating. They have a chart that shows how the boost is adjusted at sea level vs 10,000 ft to roughly produce the same power.
Not every car is affected. This situation is usually best observed in severely underpowered vehicles with automatic transmissions and VVT. For whatever reason ECU adjusts ignition timing based on octane of fuel, which in turn adjusts the electronically controlled shift points. Therefore with higher octane a vehicle can stay in same gear on a slight uphill section. Yet with lower octane on the same section of road engine now isn't producing enough duckpower (1 horsepower is 131.2 duckpowers) at lower RPMs to keep the same speed, and ECU starts playing with gears until it finds the one that keeps cruise control happy.
In the 4-cyl Tacoma with 159 hp @ 5,200 rpm, 180 lb-ft @ 3,800 rpm, and ~3500lb curb weight it is VERY noticeable. Come down to NC, I'll let you experience it and pay for fuel that this test uses. You'll just have to pay for fuel or plane ticket to come down here though.
Last edited:
I understand that. I get that what Garrett has is a simplification so that most people can understand it. But isn't the most important thing how much oxygen/air gets into an engine, which is the limit where it might otherwise self-destruct? However, I'm not sure how most turbos are set up where they can specifically adjust for altitude.
I was born in Wyoming, I know exactly what you're talking about lol. Some people just don't understand changes in air density.
It's not that hard to understand. a combination of high pressure and high temperature leads a fuel/air mixture to spontaneously explode when under compression before the spark ignites the mixture. If the air density is lower, the pressure is going to be lower and it will be less likely to go kaboom before the spark ignites the mixture. However, it also means loss of power unless there's forced induction to compensate, in which case the engine probably wants more than 85 AKI unless the knock sensor starts working early.
Even then, I'm not sure I've seen any recommendation to use 85 in any owner's manual I've seen in 30 years. I drove a 1989 Integra, and I remember it mentioned 86. It also mentioned using fuel with up to 5% methanol (with corrosion inhibitors); that recommendation didn't age well. Here's a 2021 Honda Civic owner's manual. It says 87 octane without any other recommendations.
Unleaded gasoline, pump octane number 87 or higher
You deduct 2 points from the octane recommendation for high altitude.
Similar threads
