Octane Rating at Elevation

upgrade to what ever octane you need to stop knock/ping is the general consensus

 

When I had my SC installed, the dealer told me it required 91 octane. This was at sea level, but it made sense to me considering the increased performance. If I can run lower (cheaper) fuel, that would be awesome. I just didn't want to void warranty or cause issues.

 

Based on my Suck, Squeeze, Bang, Blow education, the Super Charge will force pressurized the cylinder mitigating the altitude effect. As this pertains to Octane levels, it's out of my learnin.

 

Yeah, supercharger boost at low rpm..

 

I'm supercharged so Premiums for me. Le sad.

If I wasn't though I wouldn't waste a penny more on mid-grade unless I had knock activity. To do otherwise is foolish as you get no performance or mileage gains.

 

A supercharger makes its own atmosphere so it doesn't change hp level per elevation increase

 

I'm in the mountains, nearly double that. I've noticed mileage difference in other vehicles when switching octanes but I've only run 85 so far in this Tacoma. My old Impreza definitely got the best mileage at 85. I might experiment one week where I'll be doing the exact same commute.

 

There's far too many variables to say "well, I got more mpg on that tank so 91oct is better" which is what most do. First hand real world empirical proof, right? Wrong. There's just way, way, WAY too many variables for this sort of test to be considered anywhere scientific and undeniable proof.

If you don't have forced induction with the ability to increase the boost or advance timing on the fly or the ECU isn't programmed to 'know' it has higher octane rating to do these things for you then there is no gains to be had unless you have pinging which will cause it to pull timing. If you have pinging than a 'gain' can be made by simply avoiding having the ECU pull timing but that's not really a gain. That's just compensating for the other variables to keep the ECU happy which keeps it at the baseline.

 

Why people want to give more money to the oil companies than they have to confuses me.

What Ostrichsak said. +1 Here's a different way of saying the same thing - The engine sucks in and mixes fuel with the atmosphere, compresses it, sets off a spark to make a bang, then blows it out the tailpipe. (suck - squeeze - bang - blow) Bottom line what octane an engine needs is simply a math equation. If the engine is at high altitude it will suck in less atmosphere and as a consequence the squeeze will result in a lower cylinder pressure. The lower the cylinder pressure the lower the required octane. The ECU can only advance the spark so far, so if the engine doesn't ping with 85, 91 won't make a bit of difference. If the engine is pinging with 85 at altitude then something is wrong and needs to be fixed.

Oh and let's not confuse stock tacoma engines with supercharged, turbo, or modified engines. Octane needs are a completely different conversation in those cases.

 

I wish I could pay less per gal of gas for my street strip toy but unfortunately not gonna happen . Try spending $15 - $17 per gal or $150 - $170 a tank 2-3 x's a month . Doing this burns a large hole in your wallet

 

I use Ethanol free gas, and since 87/88 octanes are the lowest I find in that format, that's what I use.

 

Is have been living at 7000' since 1993, working on gasoline and diesel vehicles, and many an automotive old timer stated vehicles that use carburetors, the higher the elevation, the lower the octane.
My wife had been putting in 85 octane in her fuel injected '00 Jeep TJ Wrangler, cuz her father said to. I didn't know that and thought it ran like crap. Owners manual says 87. Full tank of 87 and the Jeep became a different vehicle.
I have never owned a vehicle with a carburetor. I have found that running higher rated octane than required never felt better, faster, quicker, etc.

 

I drove a 98 TJ Wrangler for 15 years and couldn't tell a bit of difference between 85/87/91 and I tried all of them in the quest for better performance. I stand by the math and the physics. Unless an engine is designed for higher octane gas it does not produce more power. IMO butt dynos are incredibly susceptible to hype and marketing and the oil companies are great at providing both.

 

Finally getting good air here finally !!

DA or corrected elev 4782 ft / 1556ft higher than actual elev

Rel density 87.52

No wonder why may Drag race car felt more responsive today !! . just a couple months back I was seeing near 9k ft corrected elev

 

Higher altitude has less oxygen/pressure which makes fuel harder to burn. This is also what octane does. You can get away with 85 at altitudes > than about 4000 feet. Mine runs no different than higher octane. What really chaps my hide is that I'm paying the same for 85 octane where lower elevations get 87. That's not right. It should be cheaper to drive at higher elevations.

 

I run 87 the cost is not much more than 85

 

85 will cause the 3.5 to ping like mad out here in Grand Junction during the 90-100 degree days of summer.

 

I wonder what's different about Grand Junction? I live at 4500 ft and have never had a modern car ping and I never run anything but 85.

 

I totally get what you are saying above. My manual states that the minimum octane is 87 but all engine testing and performance were conducted with 92. I would say 92 is OPTIMUM. I can get the actual verbiage tomorrow if you like. That being said, I don’t pay for gas in my truck or the Land Cruiser. It’s all free because I spend so much f***ing money on groceries.

 

I suspect it’s the heat out here on the western slope in the summer. I ran 85 for a while until I was driving through a canyon and could hear very audible pinging bouncing off the canyon walls. Filled up with 91 and the ping was gone the next time I went through canyon no ping... then for shits and giggles I filled up with 85 a few days later and the ping was back. During the same time I did some rudimentary 0-60 runs and 91 was without a doubt smoother and slightly quicker.