Octane, whats what?

[Matster]

So I read some of the other threads a while back and didn't really have this question answered or perhaps didn't understand the the answer.

I am currently burning Sunoco's 94 which supposedly has 20% ethanol. I read that this effects the actual octane level of the fuel and that I'm probably not getting a true 94 because it doesn't burn the same as gasoline. If this is true, would I be better off burning Shells 91 Octane that does not have any ethanol?

My Sunoco is gone, being re-branded to Petro Canada, will now have two catty corner to each other at the same intersection.

[fielderLS3]

Burning ethanol has the effect of increasing octane, not decreasing it. If anything, the Sunoco 94 with 20% ethanol is probably 91 octane gas, and the ethanol raises the overall octane to 94.

Also, are you sure there is a 20% ethanol content? I don't think non E85 cars are rated to run on anything about 10%. (at least in the US, I'm not sure if things are different in Canada). If it were my car, I'd use gas with no ethanol anytime I can find it. A 20% blend may effect your warranty.

[Matster]

Originally Posted by fielderLS3

Burning ethanol has the effect of increasing octane, not decreasing it. If anything, the Sunoco 94 with 20% ethanol is probably 91 octane gas, and the ethanol raises the overall octane to 94.

Also, are you sure there is a 20% ethanol content? I don't think non E85 cars are rated to run on anything about 10%. (at least in the US, I'm not sure if things are different in Canada). If it were my car, I'd use gas with no ethanol anytime I can find it. A 20% blend may effect your warranty.

Sorry you are right it is 10% ethanol added to 93 Octane.

[Octaneman]

Originally Posted by Matster

Sorry you are right it is 10% ethanol added to 93 Octane.

Its supposed to be 10% added to 91 octane, you will also consume more fuel as the motor see fuel by weight, and ethanol is 34% oxygenated.

[Moonlight]

I use petro-can 94. i believe it has 10% ethanol. its supposed to be somehow good for your engine. I wanted to get pure octane but there is just none around here. the next best is probably Shell 91 which does not even meet the requirement.

[CanadianCamaro]

Sunoco Ultra 94 / PC Ultra 94 (same thing) is "up to 10% ethanol by volume" I believe. Adding ethanol increases octane rating but as the ethanol content rises a larger volume is required to produce the same energy. I am not an engineer but I have heard no claims that ethanol burns and less (or more) cleaner than pure petroleum based fuel. The basic rule of thumb is higher octane fuels burn hotter and cleaner - period. So to answer your question I personally feel that you're best to stick with the 94.

Any gasoline engine will burn ethanol fuels including those with content higher than 10%. But of course their computers are not optimized to burn higher ethanol content fuels and as such fuel mixtures are not adjusted properly and as such can cause damage. Same concept as when I was a kid and accidentally filled the gas powered riding mower with diesel . It still ran, the problem was shutting it off!

[SQUALO]

To start I'm no engineer either, however, it's been said that ethonal burns cleaner for the environment, it's a renuable resource. However, it's been claimed that high content of ethonal fuels can break down engine parts over time. It's best to stick with fuels without ethonol; also read my posts(#28 & 29) in this other thread, which has a response I got from an e-mail to Petro Canada ( when they were on my good side).

http://www.camaro5.com/forums/showth...t=75204&page=2

I'm personally staying away from Petro Canada & Sunoco fuels.

[Dave Wilson]

At the risk of bein' F o' S! I believe the 'up to 10% E' is just a marketing ploy by the E industry! They've produced a product the the P industry can help them market (green) and make them them both $$!. My old F 150 would run on overproof also! We are all being manipulated by mega corps! But hey, as long as it doesn't void yer warranty....right? A retailer friend has recently told me that 'E' will be the new kid on the block country wide and will undoubtably purvaid every octane level. Enjoy yer V8's while they last.

[Rampant]

Not sure if everyone understands "Octane". It is in fact a knock intensity value. Or a value to rate its ability to with stand predetonation.

It is not an energy value. As some think it means more power. If you motor is designed for regular, you will get more power from regular!

What are higher octanes for? They are for higher compression motors so that you can make more power with the addition of compression, with out getting knock or predetonation while having a controlled burn.

So now that that is cleared up. We can discuss the different fuels out there. Ultra 94 does have ethanol in it. Ethanol has a lower energy content than typical gasoline which typically uses aromatics to boost its octane value. So as mentioned by others you need to use more of the 94 to get the same energy value or calorific value as the 91 Shell, but since you can bump your compression with the 94, you have a chance to make more hp with the 94. You are just going to use more of the 94 all the time for typical tooling around.

I use 94 in my LS7 as it has a compression of 11.4:1 and I feel safer with it. I might be able to tune it for 91 shell and run rich to cool the chamber to reduce the risk of detonation, but now I am going down another path. You can also run more aggressive timing with the higher octane. There is no magic bullet, you pick your poison.

If you run a much higher octane than needed, it will make less power and likely create deposits because the combustion will be incomplete, and make things even worse in the long run.

This is from memory and has been 25 years now since I took it in thermodynamics, but I do still mess around with it playin and tuning my toy.

Better technical details here.

http://en.wikipedia.org/wiki/Octane_rating

We could also discuss E85 and its potential, but I leave that alone for now.

[DGthe3]

Octane used to refer to the amount of actual octane (C8H18) in gasoline. Octane was harder to ignite than the lighter hydrocarbons in gas (mainly heptane, C7H16). 91 octane would have contained 91% octane. As fuel had more and more additives, this method became less and less meaningful. So they went to a standardized octane rating system. This rates a fuel based on how hard it is to ignite, relative to 100 octane. By using ethanol or heavier hydorcarbons (like nonane, C9H20) it is possible to achieve octane ratings in excess of 100 (like race gas, for example) without any actual octane in the fuel. I won't complicate matters further by going into RON, MON, and AKI.

But the short version is, if it says 94 octane, it will have the same anti-knock capacity as any other 94 octane regardless of how it got that rating. It all gets taken into account.

Originally Posted by CanadianCamaro

Sunoco Ultra 94 / PC Ultra 94 (same thing) is "up to 10% ethanol by volume" I believe. Adding ethanol increases octane rating but as the ethanol content rises a larger volume is required to produce the same energy. I am not an engineer but I have heard no claims that ethanol burns and less (or more) cleaner than pure petroleum based fuel. The basic rule of thumb is higher octane fuels burn hotter and cleaner - period. So to answer your question I personally feel that you're best to stick with the 94.

Any gasoline engine will burn ethanol fuels including those with content higher than 10%. But of course their computers are not optimized to burn higher ethanol content fuels and as such fuel mixtures are not adjusted properly and as such can cause damage. Same concept as when I was a kid and accidentally filled the gas powered riding mower with diesel . It still ran, the problem was shutting it off!

You are right. But ethanol is more efficient when looking at the big picture. Few consumers think like that though. They see a ~3% drop when using E10 vs E0, the cost savings are only seen by the oil companies, unlike with E85 which can be significantly cheaper than regular gas. So for you and me, the fuel isn't cheaper and it doesn't go as far. Yet for Sunoco, the profit is higher and brings people back sooner. Wonder why they like it so much ...

[Matster]

Thanks everyone for the input, it has been really helpful. The main reason I was asking this is because I'm considering a tune and before doing so need to decide whether to stick with 94 or switch to 91. Will stick with the 94, this isn't my daily driver so a few extra bucks on a tank full isn't going to break me.

[SQUALO]

Originally Posted by Matster

Thanks everyone for the input, it has been really helpful. The main reason I was asking this is because I'm considering a tune and before doing so need to decide whether to stick with 94 or switch to 91. Will stick with the 94, this isn't my daily driver so a few extra bucks on a tank full isn't going to break me.

Let us know how the tune goes.

[StevenMarrocco]

sorry for being the new guy around the block, but can anyone recommend me what type of gas to put in my 6 banger!
Thanks in advanced!

[Sterling]

Originally Posted by StevenMarrocco

sorry for being the new guy around the block, but can anyone recommend me what type of gas to put in my 6 banger!
Thanks in advanced!

A lot of us have been running the 93 octane since it was noticed that the knock sensors are more active using the 87 octane causing it to pull some of the timing. It will run fine on the 87 octane, but with the higher octane fuel it has a little more power. I can feel the difference when I'm short shifting... it won't bog down with the 93 like it will with the 87. The choice is really up to you.