Regular gas lasting longer than Plus?

www.pure-gas.org

 

If you notice (at least those in AL) are mainly marine stations. Ethanol has caused great harm to many marine engines, particularly those that are older and which don't have fuel lines that can tolerate the acidity of alcohol + water... I would NOT fill my truck up at those, the prices are typically $2 MORE than the normal going rate, frequently hitting $5 bucks a gallon.

 

The main advantage to ethanol is its high oxygen content. That's why many racers run alcohol, as it is almost like a poor-man's super-charger.

Only way you can get more economy per gallon of fuel is to extract more energy. That is basic physics/chemistry. Octane slows the progression of the combustion flame, nothing else. Doesn't add to or detract from the energy content of a gallon of gas.

ideal A/F ratio for gas is 14.7:1 of course. If you want to run richer to cool the combustion temps, that's a sloppy way of preventing preignition, but it works. Better is to retard the timing so that the primary power pulse occurs right at TDC, not earlier where you get pinging.

 

Higher octane gas is supposed to combust faster, therefore creating more power and piston response in engines that demand this type of quick firing to run properly. (Higher octane gas will be drank up quicker in theory.) That's why it's required for high performance engines. But, like the others said, it'll make no measurable difference in a Tacoma, or any stock, street driven vehicle the average Joe owns today. Save the money and go with regular octane, it's all you'll ever need!

 

I'm gonna have to disagree with you. It does not burn faster, but it burns longer. Chem 1301. higher the octane, the longer the chemical chain.. so it burns longer. In high compression engine needs this as it has more oxygen in the cylinder. Add boost and higher octane is a must. If you go into higher climates like Colorado, you will see lower octane levels because of lower atmospheric levels. (not so much less oxygen, just less dense) So if you add 7psi of boost, the fuel will burn faster as there is more oxygen. A higher octane level is needed for this so the fuel burns longer with the same amount of fuel.
Now you might feel like you're getting more power, and you probably are(mostly a smidge bit of torque), simply because the ECU is advancing just a slight bit more than normal. ( This is where knock sensors come into play) This is minimal. But with a normal aspirated engine, and the longer burn of the higher octane, most of that is going straight out of the exhaust. I can relate this to a diesel as that's my daily driver. You get power from a diesel with more fuel. (more diesel is similar to more octane) The more fuel you add, the more power. BUT to add more fuel, you have to add air.(So you add a turbo to add air so you can add more fuel) So when you see guys pouring coal down the street, they're dumping tons of diesel in the motor with really no added power. And just wasting all of it.
So for daily driving, there might be a minimal increase in GPM. Now if your towing a trailer, have a heavy load, or driving in steep hills, bumping up to a slightly higher octane might give you a better increase in MPG. This is all something you would have to figure out with trial and error on a personal basis. If it works for you, go with it.
And since ethanol was brought up. If I had the option to go without, I would. I really started seeing issues with my truck when that was introduced. Especially loss of power.

 

That's backward. And that backward idea is the reason for octane boosters. If the fuel/air mixture ignites too quickly, before the spark plug fires, you get more of the power impulse before TDC which tries to force the piston back down the wrong way rotation-wise, which creates that rattling noise you hear. This can be caused by pure compression temperatures, or by an imperfection or carbon deposit that retains heat and aids pre-ignition and the "ping". That is the piston beating on the wrist pin, connecting rod and crankshaft. Higher octane slows the burning down and raises the temperature needed to produce pre-ignition. Alky burns cooler since it is less dense, energy-wise. And it provides part of the oxygen needed to burn when it breaks down (a small part, one O atom out of 7 needed per molecule of ethanol).

In any case, octane is what is required to prevent the compressed fuel/air mixture from flaming up before the spark plug fires, that causes the pressure to build way before the piston reaches TDC. Or, if you advance the timing too far, you produce the exact same problem but now it is caused by the heat of the spark rather than the compression process. A pretty common octane booster today is ethanol. It has EXACTLY that property, which prevents the damaging "ping".

 

When I was on a Subaru/GT forum I'd love watching these debates. I truly appreciate the information in this thread.

Long story short: our stock trucks are perfectly fine with 87 (or 85 in higher elevation) and running higher octane has no benefit.

If you're boosted obviously you need the higher octane.

^ that is the result of everyone one of these discussions.

 

Since you are discussing Subaru, my 06 Forester, which is supposed to use 87 octane, will throw a check engine code P0420 whenever I used 87 octane fuel. If I use a higher octane, no check engine. Discussed with my mechanic, who stated it was due to the ethanol in the fuel. CAT was replaced at 90 k with OEM cat. I'm not paying another grand for a new catalytic converter if it runs fine with no CEL on 89 or 92 fuel. I'm trading that POS in next year for a honda or toyota. Only benefit to Subaru is the AWD, which is second to none in the snow. I'll just stay home if its snowing.

 

Well, yes and no depending on how you're looking at it. If 1 oz of 85 contains 10btu and 1 oz of 91 contains 20btu then you can get twice the work down with the same amount of 91 as 85. Obviously making up numbers here. So his argument is correct. And I'm reading it as I explain it to people, that if it (more power in higher octane) were true you would use less throttle etc. But the energy content of 85 and 91 is identical so the argument is to show that the energy content is actually the same. This would be easier in speech than in writing.

What the octane does do, assuming your engine is a modern style with variable timing, is all the engine to produce more power. But to get that extra power, you need to burn more fuel, so economy will drop. And if your engine is maxed out at 85, then 91 won't do a thing. It's about letting your engine do what it can, not making it do more.

My mustang (recently sold) got about 21mpg with 85. 18 with 91, doing my best to drive the same. What that confirmed for me was the engine was getting as tired as I thought it was. The engine was struggling, the harder to ignite fuel was making it work worse than the easier to ignite.

My new car is 91 minimum(twin turbos woooo!) and around town I get about 18, much better on the interstate. BUT, it's a fun car to drive so I find myself driving like a butt entirely too often. I wouldn't be surprised to see my mileage improve as I get tired of the car

 

You just posted empirical evidence of personal experience getting better economy with lower octane while spouting the exact opposite. Nice job.

 

I'm just gonna walk away from this thread, it's frightening the amount of anecdotal information and hearsay. Do what makes you happy

 

Well yes and no

There are numerous studies out there that show the same. If an engines ignition system (includes compression etc) isn't up to the task you can harm the numbers by using higher octane. That's nothing new. That vehicle was no longer up to the task of efficiently burning the higher octane. The energy content in the 2 fuels is the same, the engine's ability to use it wasn't.

Engines are like people, they're all a little different. And the wankel is like that guy that everyone thought was smart but really wasn't

 

I feel like the thread has been answered. But one thing that wasn't addressed, what is the best engine oil for our trucks?

.......wait for it

 

GRENADE!