Had the truck two weeks , it runs better on 89 octane

Dont you need less octane at altitude?

 

Correct, it's why they can get away with selling 85 in the mountain states

 

You are correct, it isn't about power content of the fuel. It's about how much the ECU retards ignition.

 

No idea how but I've been getting 26 mpg on 87. Finally off that winter gas

 

I'm running the OV tune with 91 octane... it is a big boost from 87 octane (with the tune). Never tried 91 on OEM tune. But i bet it would make some difference.

 

Absolutely incorrect, NIST established the weight and measurement program that state environmental agency's follow. Each state varies on implementation. In general random samples are taken and either analyzed on the spot or sent to a lab for testing per ASTM standards. Octane is one among many tests performed. Non-compliance penalty varies, usually a notice of non-compliance and a grace period to correct the deviation. Monetary penalty come in to play for repeated or intentional non-compliance.

The whole mix thing is generally true, although less so today with ethanol around. If they do blend at the pump they tend to error on the side of extra 91 to avoid trouble. Depending on the area and ethanol the mid grade may be mixed in the carrier tanker at the terminal so that station can offer ethanol free grades for recreational vehicles.

 

I think I blew up my head gasket on my 96’ taco 3RZ-FE from 85 gas (in NM at the time) and/ or from not replacing the coolant enough. All my tacos from now on get 91 and get fresh coolant every 2 years. That’s just me and my paranoia from spending so much $$$ on rebuilding the engine. I’ll wait in line at Costco and spare some cost on premium though. It had almost 200k miles on it though.

 

I use 86

 

Having made gasoline for about 20 years, and running variously modified vehicles before and since if a vehicle is set up properly octane is all about compression. If an engine is designed for 87 and you haven't made significant changes to the operation of the engine then run 87. Everything else is a waste of money. The station and refiner will thank you for using the higher octane, but that's the only benefit you'll receive.

When I was young and dumb I used to get racing fuel at a place called SoCal racing fuel. I'd fill my '68 Nova up and take it over to Brotherhood and I swore it made the car go faster. It didn't, I probably shifted better. Once I studied chemistry and got into the petroleum industry I figured I had just wasted my very limited funds to no advantage.

 

85 works best in my truck.

 

typo - I’m so baked.

less peak cylinder pressure (lower engine compression) At elevation = lower min. Octane required. I use 87 heading up the hill, 91 around town.

Science says 91 shouldn’t feel more “smooth,” but it does seem smoother considering my driving style = shifting at 3-4rpm 24/7. Placebo? Sure.

 

3-4 rotations PER MINUTE? Boy, no wonder you're feeling a rough ride

 

Well there's your problem, you forgot the part where you twist the distro cap to advance the timing. You should have taken engine theory from the mechanicals.

 

There was a time that if a station had a Chevron sign on the building they had to sell Chevron gas. Not so much any more.

But here's the real kicker. Let's say refiner A has contracts for X amount of gasoline. But he's short. So he borrows some for refiner B. And that blend of what ever ratio ends up in the stations tanks. Later refiner B is short so he gets some from refiner A as payback. They do the same thing with crude oil, diesel and any other distillates.

Then you can and the fact that in many places Refiner A and Refiner B use the same pipelines. Now depending on whats going through the pipe on consecutive pipeline movements they may or may not put a plug, usually water, in the line between the movements.

An example of how much of it is marketing is the old Shell gasoline with "Platformate". Now every refiner reforms gasoline (increases the octane by altering the molecular structure). But most called it just that reformate. It's all done with a platinum based catalyst. Shell just trade marked the name for what everyone was doing and spent a fortune advertising how much better it was. It was a good ad campaign as lots of folks would insist on Shell gasoline.

 

Are they pushing biodiesel on the pipe lines much yet. I deal with fuel contracts for emergency equipment and avoid it at all costs. Not a big fan when the FAA caved on it. It getting harder to find sources that test bio free.

 

No, I pretty much had figured out timing by them. But dwell so illusive.

 

Meh, the direct injection can actually lower the octane requirement. 87 is fine.

 

87 clear gas (ethanol free). Altitude ranges from 3000 to 4500 above sea level. Truck drives great.

 

Does it knock? That is the point of octane ratings at 600/900 rpm tests. If you are getting a noticeable difference you might need a tune up or maybe you are on summer mix?

 

Octanes and elevations are a strange thing. Basically at sea level, the engine makes a certain amount of HP, generally higher than at higher elevations. Take that same engine with the same octane at 8000 feet and the HP can diminish by as much as 10-15%.

I live in San Antonio at 700 ft. I just did a job outside Denver at 6000 feet. I was up there for almost two weeks and drove about 300ish miles during that timeframe. I got better mileage in Denver around town with Colorado 90 octane fuel (highest available there) than I do back home in SA with Texas 93 octane. Similar driving habits, highway and city. I run premium because I run an OVTune 91 octane tune.

All in all it seems like the variables from truck to truck, driving style to driving style, fuel brand to fuel brand, location to location, etc..., are too many to categorize into any kind of system that one could truly compare with any sort of accuracy or continuity.