Home Forums Hunting & Shooting Hunter's Campfire Octane Rating

With all the attention on your fuel prices (and ours, thanks to your President affecting prices worldwide) I've noticed something that I hadn't picked up before, and that is the low octane rating of your gasoline in the US. Correct me if I'm wrong, but your standard is about 87 RON, and premium is about 91 - 94. Is that right?

FWIW that is lower than here, where 91 is "standard" and then there's E10 (10% ethanol) at 94, and then 95 and 98. A lot of cars here require 98, especially European or anything with any sporting pretensions. My wife's car needs at least 95 (mine's a turbodiesel)

What octane number is recommended there for, say, European cars? Are they detuned perhaps, to run on the lower-octane fuel?

We use the R+M/2 rating for octane, not RON. They aren't the same.
Our gas has the same octane as yours, we just use a different method to calculate it.

Low octane is fine with today's computer controlled low to mid compression ratio engines and their variable valve timing.

We typically have five grades of petrol fuel in the US - 87, 89, 93, nonethanol 90 and E-85. Our basic fuels (87, 89, 93) have up to 10% ethanol content while E85 can have anywhere from 65% - 85% ethanol.

Octane recommendations is largely a game. ECU (Engine control units) constantly adjust air/fuel mixture and spark advanced based on a bunch of factors including mass air sensor, inlet temperature, engine load, knock sensor, emissions control, and fuel octane to name a few. ANY modern petrol engine can burn any grade of petrol based fuel. The only caveat to that is - it's not a great idea to run E-85 in a standard engine not designed for it - Flex Fuel Vehicles.

Car manufacturers specify fuel grades in order to comply with EPA emission standards, otherwise, it's a lot of smoke and mirrors. Point is, even if the manufacturer recommends 93 Octane only, the ECU will adjust timing to compensate if you run 85 octane and that includes turbo engines. You will lose some max horsepower at high RPMs as the spark timing will be retarded to control detonation, but otherwise for daily driving, you won't notice the difference - only the savings on fuel costs.

Engine purists will argue octane ratings but in the real world, it is a lot of marketing nonsense by the energy companies and the climate nazis.

The way we rate octane and the way the rest of the world rates it aren’t the same. 93 octane in Europe/Oz isn’t the same as 93 octane in the US. Out basic gas is pretty much the same even though they call it 91 and we call it 87.

Most euro luxury cars in the US call for 91 octane at the minimum which is equivalent to about 95 everywhere else.

In eastern Idaho we can usually choose 85, 87, or 91. I've most always ran the 85 octane stuff but realized last year all my vehicles say to use at least 87 which is migrate here and usually at least 20 cents a gallon more. I think ours is rated all the way down to 85 because we are at higher elevation. I'm guessing gas doesn't detonate as easy in the thinner air so we can run a few points lower.

Bb

When you get above about 1800 to 2000' in elevation, you can drop 2 points in octane. Most of the stations in southern Idaho sell 85. The lowest point in so. Idaho is at the OR border at about 2100'. 85 works fine there. In no. Idaho, the lowest point is at Lewiston, about 700'. You need 87 there.

Ethanol Free boat gas has been much cheaper than the 10% Ethanol gas at the pump (i.e. they haven't raised the prices on it yet).

I filled up there with no lines while the steeple waited at the pump to pay more $.

The brain is a power thing for those trained to observe situations and use their reason.

So be it.

Higher elevation area's usually sell 85 octane, because you can run lower octane at higher elevations. I'm in an area around 3k-4k feet, we get 87,89,91 (std, mid, high) octane. Area's around sea level usually get 87,89,92 . The rule of thumb for carburetors is to lean them 1 jet size per 1k feet because of the lower atmospheric pressure.

My wife's new GT Mustang is 12:1 compression and takes 91 octane minimum, Modern head designs and variable cam timing allows for lower octane than older engines. I have an old corvette that runs 11.3:1 compression with a more modern aluminum head, I can run 91 octane at 3k feet but at sea level I need 93-95 octane because it lacks computer controlled timing. In the old muscle car days premium was 100 octane and some cars came with 11:1 or more compression.

non-al gas here runs about 40 to 50 cents more than regular. It's the highest priced gas around. The only stations here that sell it are a couple that have high priced gas to start with. I use it in everything from my UTV on down.

My point was that it was $3.39 (because the price hadn't caught up yet) and the sheep waiting at the pumps for Ethanol gas were paying $3.79

Not sure what you mean by low to mid compression.
Relative terms. Low today was high in the 80s.

Ratios have crept up with the sophistication of fueling/timing systems.
High compression is an easy way to make power if knock is controlled.
DI engines can do very well that way.

I drove from the aforementioned Oregon border (2150 feet here) to Ogden a couple weeks ago. Once I got into the Magic Valley and beyond, I was surprised to see gas 20 to 30 cents cheaper than the Boise Valley.

Then I pulled into the station and saw that it was 85 octane. 85 octane appears to be standard through the upper Snake River region, and on toward Salt Lake.

But I have never seen it North West of Mountain Home. I might put 85 octane in the 5.7 Durango if I intended to burn through the tank at high altitude. But since I only make quick trips to the area, then turn around and come home, I pay the extra and keep 87 in the tank.

Higher octane gasoline is like "magnum" gunpowder. It burns considerably slower than regular gas to avoid pressure spikes, preignition, and detonation in higher compression engines as the flame front travels across the combustion chamber. The higher octane fuel burn gives a steady push instead of a quick jab at the pistons. Computer controlled valve and ignition timing reduces the danger of engine damage when running low octane gas, but they're mostly intended to control exhaust emissions, not to keep cheapskates who insist on saving a few cents a gallon by running the wrong gas from destroying their engines.

I just got some 100 octane 6.30 a gallon..works well in small planes... so the higher in elevation u go theory is out........the higher u go in numbers..the slower the burn...

The high octane avgas has nothing to do with altitude- - - -it's for turbocharged engines that have the equivalent of very high compression ratios with the boost turned up, regardless of altitude. USAF gas engines with varible rate turbos burned 115/145 octane, with the lower number representing its use in high manifold pressure engines.

You can't equate auto and aircraft engines. That's a carrots and kumquats comparison.

I just topped off my old hunting truck in Rigby and 85 10% ethanol was $3.72 and 91 octane no ethanol was $4.39. It's up 40 cents the last 2 days. I'm going to go check all my lawn mower and 4 wheeler gas cans to see if I need to top them off. Thry get the 91 octane non ethanol expensive stuff.

Bb

Some of y'all should read this - https://en.wikipedia.org/wiki/Octane_rating . It's mostly accurate (a little missing info).

I'm near Twin Falls and 4000'. We're in and out of the Boise to Ontario area and never have any problem at all with 85 at that elevation.