About the right octane grade & Ethanol

[Hermans]

I hope to make an useful contribution with this thread.
My curiosity was triggered about getting the right octane grade..


The right octane grade

Lets take the 5.3L Vortec Gen III engine, the compression ratio is typically 9.5:1

So for old engines (pre-electronic management, carburetors ) the hand rule was always, how higher the compression the higher octane grade you need. Otherwise (with too low octane) you get pre detonation and you will hear a "knocking" sound. which is really bad for the engine. I found this old chart on the internet:



If i look at the user manual, GM is saying it will run fine on regular grade 87. According to this chart gas with octane 87 is too low for compression ratio 9.5:1 used by the 5.3 vortec engines.
But i found out, that modern engines can handle even low octane gas by means of computer management of ignition/timing and the use of "knocking" sensors. (or whatever it called for)

But still, i think (especially under stress, towing, mountains, etc) the 5.3 Vortec runs better and more economic with octane grade 90/91. What are you thoughts about that?

Ethanol

In Europe and US gasoline is still more mixed with Ethanol, in Europe regular grade (EUR95) is standard mixed with 5% Ethanol. And according to the US department of energy, in the US contains gasoline up to 10% ethanol. I think its not good for the health of the engine. Ethanol attracts water, and in worse cases you get things like vaper lock. Are there still gasoline's without Ethanol?

 

[mals]

My curiosity was triggered about getting the right octane grade...

If i look at the user manual, GM is saying it will run fine on regular grade 87. According to this chart gas with octane 87 is too low for compression ratio 9.5:1 used by the 5.3 vortec engines.
But i found out, that modern engines can handle even low octane gas by means of computer management of ignition/timing and the use of "knocking" sensors. (or whatever it called for)

But still, i think (especially under stress, towing, mountains, etc) the 5.3 Vortec runs better and more economic with octane grade 90/91. What are you thoughts about that?

...according to the US department of energy, in the US contains gasoline up to 10% ethanol. I think its not good for the health of the engine. Ethanol attracts water, and in worse cases you get things like vaper lock. Are there still gasoline's without Ethanol?

I drive and tow my Yukon LQ4 6.0L with 87. It's what the manual calls for, and I don't see any gains when I've tested higher octane. Our gas here in MA is all 10% ethanol year round. That does drop the MPG, but it's all I have access to. On my last road trip while I was towing my travel trailer one of the stations we stopped at had 91 octane that was ethanol free. I filled up with it, and really didn't notice a significant change from all the other tanks on the trip.

If you want to try for yourself you can find stations that offer ethanol free gasoline using this site: https://www.pure-gas.org/

 

[adventurenali92]

When I first bought my 2006 Denali XL with the sameLQ4 6.0 I was running 87 octane. I switched to 91 and I won't ever go back. It just doesn't feel right when I run it on 87. To me it feels sluggish and bogged down and I don't like that feeling. Feelings like I'm ruining my motor. So I stay on 91. But that's just me.

 

[Martinjmpr]

The funny thing is that people who like higher octane also hate ethanol.

It's funny because ethanol is an octane booster. Pure ethanol is like 100 or 110 octane.

I run regular E10 most of the time. I've run several tanks of E-85 and seen a ~5% - 10% drop in MPG which is usually offset by a 10 - 20% lower price (so the price per mile is the same or lower.)

I've tried arguing octane on the internet but I've given up.

Too much like religion or politics. People believe what they want to believe and they'll cherry pick any "facts" to support whichever side of the argument they're on.

 

[Rocket Man]

And let's not forget that the US measures octane different then Europe and other parts of the world. USA uses AKI (R+M/2) and Europe uses RON. My Whipple supercharger instructions state I need "Minimum Octane Rating 91 RON/MON/2". In Europe that would be the same as their 95 octane.


Measurement methods

A US gas station pump offering five different (R+M)/2 octane ratings
Research Octane Number (RON)
The most common type of octane rating worldwide is the Research Octane Number (RON). RON is determined by running the fuel in a test engine with a variable compression ratio under controlled conditions, and comparing the results with those for mixtures of iso-octane and n-heptane.

Motor Octane Number (MON)
Another type of octane rating, called Motor Octane Number (MON), is determined at 900 rpm engine speed instead of the 600 rpm for RON.[1] MON testing uses a similar test engine to that used in RON testing, but with a preheated fuel mixture, higher engine speed, and variable ignition timing to further stress the fuel's knock resistance. Depending on the composition of the fuel, the MON of a modern pump gasoline will be about 8 to 12 octane lower than the RON, but there is no direct link between RON and MON. Pump gasoline specifications typically require both a minimum RON and a minimum MON.[citation needed]

Anti-Knock Index (AKI) or (R+M)/2
In most countries, including Australia, New Zealand and all of those in Europe,[citation needed] the "headline" octane rating shown on the pump is the RON, but in Canada, the United States, Brazil, and some other countries, the headline number is the average of the RON and the MON, called the Anti-Knock Index (AKI), and often written on pumps as (R+M)/2. It may also sometimes be called the Posted Octane Number (PON).

Difference between RON, MON, and AKI
Because of the 8 to 12 octane number difference between RON and MON noted above, the AKI shown in Canada and the United States is 4 to 6 octane numbers lower than elsewhere in the world for the same fuel. This difference between RON and MON is known as the fuel's Sensitivity,[4] and is not typically published for those countries that use the Anti-Knock Index labelling system.

See the table in the following section for a comparison.

Observed Road Octane Number (RdON)
Another type of octane rating, called Observed Road Octane Number (RdON), is derived from testing gasolines in real world multi-cylinder engines, normally at wide open throttle. It was developed in the 1920s and is still reliable today. The original testing was done in cars on the road but as technology developed the testing was moved to chassis dynamometers with environmental controls to improve consistency.[5]

Octane Index
The evaluation of the octane number by the two laboratory methods requires a standard engine, and the test procedure can be both expensive and time-consuming. The standard engine required for the test may not always be available, especially in out-of-the-way places or in small or mobile laboratories. These and other considerations led to the search for a rapid method for the evaluation of the anti-knock quality of gasoline. Such methods include FTIR, near infrared on-line analyzers (ASTM D-2885) and others. Deriving an equation that can be used for calculating the octane quality would also serve the same purpose with added advantages. The term Octane Index is often used to refer to the calculated octane quality in contradistinction to the (measured) research or motor octane numbers. The octane index can be of great service in the blending of gasoline. Motor gasoline, as marketed, is usually a blend of several types of refinery grades that are derived from different processes such as straight-run gasoline, reformate, cracked gasoline etc. These different grades are considered as one group when blending to meet final product specifications. Most refiners produce and market more than one grade of motor gasoline, differing principally in their anti-knock quality. The ability to predict the octane quality of the blends prior to blending is essential, something for which the calculated octane index is specially suited.[6]

 

[mdnitedrftr]

My own view on the matter...

It's a mass produced small block Chevy. Its a very simple engine. It's not a Ferrari. Maybe one of these days I'll try throwing 91 in there and see what happens. Maybe I'll notice a difference and eat my words. Probably not though.

 

[RaiderRodney]

I have to agree with the majority here. These aren't high performance nor turboed engines that require high octane fuels. They are designed for minimal octane fuel and will most likely perform best with it. I've personally never had a problem with 87 in my 5.3 Hoe.

 

[Rocket Man]

I've always gone with what's recommended for my vehicle. My owner's manual states minimum 87 octane, and for the stock engine on the stock tune, that's what I ran. NBS Escalades with the LQ9 have a higher compression and require higher octane fuel, as stated in their owner's manual. Then I did some engine mods and bought an Autocal from Blackbear. Initially, I had a choice of 2 tunes- 87-89 octane and 91+ octane tunes since I could load the tunes myself. I noticed that when I loaded the 91+ tune and ran premium gas for it, I had a bit more power but I believe that was because the tune changed the timing to take advantage of the higher octane. I don't think I would have noticed the difference without the 91+ tune. Now, with a blower, I have to run 91+ or I'll damage the engine when under boost so I just have 1 tune available. My advice to anyone that's unsure, is to go with what's recommended- if it's stock, go with the owner manual. If you have a tune, go with the tuner's recommendation. And if you have a blower, that trumps all else but at that point you should be working with a reputable tuner anyway.