Gas Octane

Just picking a few tanks don't mean much. Comparing a worst tank to a best tank seems to be what barlett is doing. Running E10 tank after tank I can see similar swings in mpg. Too big of swings to be able to conclude minor differences in fuel.

Simply commuting at a different time of day when traffic congestion is different makes a big difference with my mpg. Throw in the changing temperature, some wind or lack of and tank to tank comparisons don't tell much without a lot of tanks and still it isn't precise enough to claim "18.34 cents per kilometer on 87 and 13.04 cent per kilometer with 91"

A scangauge or ultragauge is pretty useful in determining differences in gas. With E0 my fuel adjustment is around 2%. With E10 it is about 8%. You would see fuel adjustment differences if one station was worse or if 91 was better than 87.

Non-ethanol vs ethanol of course will show an improvement, but 4-8% is more likely.

Here is a graph of my tanks since 2005. Not very consistent with E10. I had E0 for several summers from 2005-2008.

 

Your calculations look right to me.

What doesn't seem right is how poor your mpg was with 87. 17-18 mpg imperial is a miserable 14.4-15.2 mpg US. Lots of people with your setup get way better than 15 on 87 all the time.

When was the last time you ran 87? At your 2200 ft altitude octane requirements go down and octane increases do less.

The usual 91 octan benefits are either E0 which helps 4-8% and with automatics under load in the right rpm range there is less downshifting. You have a stick so you control the downshifting, are you downshifting less? E0 87 should get you the same 4-8%.

I don't doubt you have gotten 26.9 mpg imperial just hard to believe you were so bad with 87.

 

22.24 imperial is 18.5 US. With a lift/tires/6-spd that is pretty normal.

 

I get 16-17 US mpg

 

Normal if you drive like an 80 year old like Bartlett.

 

IC

 

I haven't gone through all 40+ pages of posts, but from the pages I HAVE read, it seems that a bit of engine operation and software control information may help to clear up some of the debate, and questions.

Let's start with a typical automotive engine. Our engine in question is made by Widget Auto. It is a 4-stroke, naturally aspirated engine (No turbo or super charger) and it has standard valve timing (No VVT system) The compression ratio is 9.5:1 and it is able to run on both 87 and higher octane fuel. The designers have it programmed to run best at 91 Octane, with 30 degrees of advance ignition timing.

So here you are in your Widget Auto and you have been running 91 Octane, but would like to try saving money by running 87 octane. Your engine runs as expected for a while (still has some 91 octane left) but when it finally is diluted enough to be down to 87 octane, your engine computer gets a signal from your knock sensor saying that there is a little bit of ignition ping, so it retards the timing until the ping goes away, and you are now running just fine, but your timing is only advanced by 20 degrees to prevent the ping. The difference of 10 degrees of advance has you with slightly less power, and you find that the engine doesn't have the "pep" you once had. So you go back to 91 octane, and the timing eventually goes back to normal.

Lets use the same base vehicle, but this time the engineers have designed it to run best on 87 octane, at 20 degrees of ignition advance. You have heard rumors that running 91 octane will improve your power, and fuel economy. Again it takes a short time to get the fuel "diluted" to the higher 91 octane. Now the engine computer has no idea that you have put this 91 octane in your tank (except the few cars that actually have an octane sensor) It runs the timing up to it's normal 20 degrees of advance, there is no ping, so all is good. It does NOT continue to advance the timing to get more power however, so no noticeable change in performance.

Now let us look at the more advanced vehicles. Octane sensors are more abundant, more vehicles are software designed to advance timing until ping occurs, then retard it to the point of no ping. Others are designed to run on the 91 octane, but don't respond to the higher octanes due to the second engine example above. Some have Variable Valve Timing which can actively change the characteristics of compression ratio. Some are not naturally aspirated and have turbo or superchargers. Some gasoline engines are now having direct injection (similar to the diesel engines) which allow an even greater control over ping.

There are so many different types of engines today. Each designed by engineers to respond differently. What works on one car, may not work on another. One Tacoma may be like my 1997, where it is designed to run on 87 octane, and has no octane sensor. I have tried running higher octane fuel, and have seen no change in performance, or fuel economy, even over several successive tanks. Another Tacoma may be supercharged, and will have to run 91 octane or better, or it will suffer from ping. And yet another may be naturally aspirated, but still the engineers have programmed it to run best on 91 octane, and running 87 in it will cause a loss of economy, and performance.

The point I am making is that even within the small world of Tacoma trucks, there are variables in engine and software design through the years that will change how our trucks respond to fuel octane. Not everyone drives the same either, and this also affects fuel economy. "Joe" tows a trailer all the time. "Steve" lives at a higher altitude, and his engine responds differently due to the lower density of air at higher altitudes. Assuming the both have identical trucks, fuel requirements and economy will be different.

 

^

How did you know my name was Steve?

 

LMAO, I had no idea. It was a name I pulled out of a hat. haha

 

For any Canucks interested, Marketplace is doing an episode on premium tonight, and they came to the conclusion there is no difference (ultra-short version).

 

http://www.cbc.ca/m/touch/canada/story/2012/10/30/marketplace-premium-gas.html

 

Hardly a conclusive test, just some guy running some unknown amount of regular and an unknown amount of premium.

There are fuel cycle tests that can precisely conclude these difference. Gas companies don't want to prove premium doesn't matter or they'd have proof it does, which they don't.

As I commented before, anyone with a scangauge or ultragauge should be able to see a difference through the fuel adjustment percentage. It is clear as day between E0 and E10 with my scangauge. E0 uses around a 2% adjustment. E10 more like 8-9%.

 

Yup. The problem is that there is no blanket statement you can make about high octane fuel. In some cars it makes a difference, and in some cars it doesn't. Several years ago, Car & Driver did an article on this using several cars. Results were all over the place, from more power, to no difference, to less power, depending on the vehicle. Here's a link:

http://www.caranddriver.com/features/regular-or-premium

The reason fuel companies don't make claims is that it's not up to them whether higher octane makes a difference. It's up to the engine designers.

 

The only time lower octane will be the same as higher octane is a engine design that is old and does not have variable timing and the ability to pull or add timing via the ECU.

ANY modern motor is going to benefit from higher octane, period, end of story.

You can take my challenge if you want, roll up to the nearest DYNO throw in 87, drain, throw in 91-93, watch your power go up.

Whatever helps you sleep better at night is one thing, but telling yourself that YOU can't tell a difference because your BUTT DYNO says your truck is the same on 87 as 91 is just guessing at best.

All modern engines benefit from higher octane, which lowers IAT, which allows the ECU to add timing, every degree of timing added = power and tq.

I have been working around DYNO's for years, never in my life have I seen low octane in a modern motor make more power.

 

Does my 2006 2.7L (2TR-FE) have an ECU with the ability to advance (or otherwise adjust) the ignition timing depending on the grade of fuel in the tank? Does it have a knock sensor or octane sensor? No, it does not. So why would I run premium?

End of story.

 

You have it backwards. The higher the elevation the lower the octane required. Less atmospheric pressure equals less cylinder pressure therefore less need for octane. That's why regular octane is 95 in mountain states and 97 at sea level.

Your credibility is not so high after that gaffe.

I've built a few motors too, my latest small block mopar with 10.3:1 compression doesn't need more than 91 at 5800 feet at Bandimere speedway, but 93 might not be enough at sea level.

Many modern engines do not add timing, my I4 among them. Engines designed for 87 don't benefit. Your blanket statement that ANY modern engines benefit is simply FALSE, not FACT, end of story, period.

 

I make more power with race gas at elevation, that is a fact.

I have dozens of DYNO sheets to prove it. We do lose power at elevation, in some cases we have to use race gas to achieve power we were making on 93 at sea level. Higher octane is almost always better, even If you question my credibility.

Higher octane is NOT required for elevation, especially if you have fixed timing.

Going by your theory, a car making x amount of power with 93 octane at sea-level should make more power at elevation.

One of my cars making 450WHP made 390WHP using the same gas, only difference was elevation. Same type of dyno.

Anyway. I have just stated what I see on the DYNO.

 

Yes it does, almost all modern engines do. And yours definitely does.

This is right from Toyota on your engine;

System Outline 1TR-FE 2TR-FE (unleaded) 2TR-FE (leaded) EFI Electric Fuel Injection An L-type EFI system directly detects the intake air mass with a hot wire type air flow meter. The fuel injection system is a sequential multiport fuel injection system. Fuel injection takes two forms: Synchronous injection, which always takes place with the same timing in accordance with the basic injection duration and an additional correction based on the signals provided by the sensors. Non-synchronous injection, which takes place at the time an injection request based on the signals provided by the sensors is detected, regardless of the crankshaft position. Synchronous injection is further divided into group injection during a cold start, and independent injection after the engine is started. ESA Electric Spark Advance Ignition timing is determined by the engine ECU based on signals from various sensors. The engine ECU corrects ignition timing in response to engine knocking. This system selects the optimal ignition timing in accordance with the signals received from the sensors and sends the (IGT) ignition signal to the igniter.

 

Of course you lose power, I never said otherwise. My theory?

You theory is like saying you can gain power back after dropping your compression from 11:1 to 9:1 by using higher octane gas. Of course the higher octane goes to waste. If you gained back power with higher octane at higher elevation with more advance that just means you should be running even higher octane at sea level with more advance.

 

Lower compression allows you to run more timing, more timing = more power. Higher octane allows the ECU to add more timing.

If you go up elevation and your car sees more knock, it will pull timing, you can offset this a bit via higher octane.

Anyway, I agree partially with what you are saying, I stand by my higher octane gas will help you at elevation, especially for a tuned car.