Fuel for mountain towing.

[Vaquero]

RAM 1500 5.7 Hemi.
We're headed to about 8000' elevation from 1200'.
Would a higher octane help once we approach 5000'?
Would the truck relearn curve be detrimental?
Is thinner air better or worse for higher octane?

Lot's of questions, but thanks in advance.

[Each]

I’ll start by saying I’m far from an expert, but, 85 octane is available in some high altitude states like Colorado because, in the thinner air, there is less of a need for a higher octane. If you normally run 87, I’d just keep running it.

One issue you may find is that a non-turbo engine looses power at higher altitudes because there is less air available to mix with fuel. Diesel engines usual have turbos which compress the air to minimize the impact but a naturally aspirated gas will be affected. I don’t have first hand experience so I can’t say how significant it will be.

[barryg]

The differing octane levels in fuel is to prevent knocking.

Theory would be the higher the altitude the less proclivity for knock to begin with due to the lower air pressure and hence less air in the cylinder compared to lower altitudes.
The higher the altitude the lower the octane you can supposedly get away with. In fact here you will find the ratings at the pump less than at lower altitude for example low tier is 85 and probably 87 where you are at, mid level 87 here is probably 89 where you are at and premium here is usually 89 and 91 where you are at. I would just use the same grade you normally use ie mid level use it here as well.if If you notice it is knocking then go up a grade. Using higher octane fuel than required will have no impact on the engine just your wallet.

[ttavasc]

You'll lose about 3% power for every 1000ft gain in elevation with the normally aspirated engine. I run the recommended 89 octane in my Hemi unless it's not available, then I use the next highest octane available which is often 88. I don't recall seeing anything in the owners manual regarding fuel requirements and altitude.

We generally have one or more trips each season which takes us through an area of 8-9000ft elevation. Things might feel a bit sluggish or like the engine is working a little harder but it is what it is. I'm just mindful of it and adjust my driving to accommodate it. Never have any issues but then again I'm only lugging around 3800 lbs.

[Vaquero]

Thanks to all.
Sounds like I can just gas up and go as normal.
I'll watch for the hp drop, but the speed limits drop to 55 for the last leg of the trip anyway.
Might not notice much.

[Colorado]

Make sure your air filter is either new or clean, towing at elevation is hard on engines because of the lack of O2. I can feel the difference in my GF's Hemi going from 6-7K to 9K and then back down to 5000FT. The engine literally comes alive as the elevation lowers and it starts to breathe better.
We replaced the stock filter with a washable AFE Dry filter that she can keep clean especially after exceptionally dirty trails. When we use her rig, It's helped significantly since the majority of our towing is above 8K feet.

[DC8Captain]

I live in CO and pull my TT at times over 11,000' with a gasoline engine. A higher octane will not help you unless you used an engine tuner to increase your towing power. If so the tuner changes the timing and mine says you won't get any increase in power unless you use high octane gas. That's the only situation that high octane fuel will be beneficial. The other thing that will help is to run with gas that doesn't use ethanol like E15 or E10. Here's a link to a gas station finder that sell gas without the alcohol.


Ethanol Free Gas Stations

[SkyBound]

Modern day engines watch for knock and pre-ignition and adjust timing accordingly. The computer will retard the ignition timing if it senses knocking, which will lead to diminished power output but avoid engine damage from the piston trying to go up while the burning air/fuel is trying to push it down. Run what the manufacturer recommends and you should be OK.

Oh, and that Hemi is going to want to downshift and REV! Let it do its thing.

[Vaquero]

Update on an awesome week.
Fuel mileage was better than expected going uphill.
Really didn't notice a decrease in power.
Gotta brag on the tow/haul mode. Downhill, more than up.
I cranked the gain up on the brake controller for the downhill run.
Not necessary. Gas engine braking worked like a charm.