Acrad

Yeah... that is some old stuff.. some EOL'd when I was in grade school... Thanks! I love looking at old operating systems.

lobuxracer

iTrader: (2)

Hook up Techstream and look at KCLV (knock control learned value). It does not lie.

Also, please stop the "premium burns slower" myth. It does not. It has a higher autoignition temperature. That is all.

And finally, why would two engines with apparently the same specifications require different fuels? Dynamic compression ratio, which takes into account cam timing, may create a condition where mechanically identical engines have different fuel requirements. When VE goes over 100% (the direct mechanical maximum), the static compression ratio is useless for determining octane requirements. Altering cam timing also alters the rpm at which the engine makes peak torque and peak power (among other things like intake and exhaust design, throttlebody diameter, and a small host of other variables). So, it is definitely possible for two engines with identical static compression ratios to have very different power curves and very different octane requirements.

It's always a good read when electrical guys start talking engines. Humor in my life is a great thing.

Craigyyy

Marketing is everything. Pretty funny article from 1990:
http://articles.chicagotribune.com/1...e-premium-fuel

One good snippet:

It makes people feel good to put premium gas in their luxury product. They feel like they're doing their car a favor, taking better care of it, giving it a treat, you name it. Seeing "premium only" on the gas lid makes people feel like they bought a premium product, something that's better than something regular.

Nobody wants to be told they have been duped into wasting money. Nobody wants to feel foolish for paying 40 or 50 cents more per gallon their whole lives. People want to feel like they've got something special going on. Owners want the extra incremental performance, smoothness whatever other placebo they can get. The premium product, opulence, warm and fuzzies are a huge part of the luxury brand image and strategy.

Htony

This debate will never end. Personally if manual says use this gas, then I use this gas. For me car is not an asset. It is consumable product. I always buy car with cash. If saving money is big concern, taking out a loan to buy a car(depreciating fast) is a big money loser. Same basic engine can be tuned many different ways. One can be tuned for peak performance, the other one can be detuned to under perform. (Think after market product) Nowadays it is even easier because it can be done with engine management software.

I drove company cars getting replacement every 3 years for over 40 years. When I was retiring I took the car I was driving on book value. While driving it for about 3 years I saved enough money in my piggy bank to trade the car and pay cash for a new car. Drive it for 3-4 years while filling up piggy bank so I can buy another new one and so on. Now getting old, time to have annual physical exam to keep my license. Don't know when I'll lose the license. Then wife will be driving for another
5 years or so. Hopefully at least 10 years driving time left between us. Then heading to nursing home I guess... Time to look for a car wife will like.

jjscsix

This article and many others I have read over the past 50 years do not agree with you. I don't claim to have the ability to prove my point, but I did not make up the notion that higher octane burns slower.
https://www.hemmings.com/blog/2014/0...-priced-fuels/

Htony

Then what does high Octane fuel does? I am sure many articles you have read are B4 the days of electronic engine management.

jjscsix

I'm trying to figure out if that is a serious question or not. Higher octane allows you to tune the engine for better performance and throttle response. Same reason as why they reduce compression to add more boost on a forced induction engine. Engine building and tuning is all about figuring out what to give and what to take to achieve the balance you are looking for.

As to when I read the articles, I did a google search and found the article above in about 30 seconds an hour ago.

Craigyyy

Right. Higher octane has a higher resistance to knock (i.e., burn prematurely, and also to burn at all).

The most vehement in favor of spending on premium fuel tend to be very sanctimonious in their arguments, which is why these discussions tend to run on for so long. Gosh, what a cheapskate you are. You bought a luxury car but won't put luxury gasoline into it, what an idiot! Hahaha, you're not even a mechanical engineer, you must be wrong and I am definitely right, you imbecile!

Of course the things they say are undisputed fact and what you have to say is rubbish or myth. You will never offer up sufficient proof or justification to their liking.

I'm not picking on anybody in this thread, but just these threads in general, particularly on other forums where the posters are less pleasant.

lobuxracer

iTrader: (2)

Science is not a consensus sport. How many of those sources are petroleum engineers?

http://www.faqs.org/faqs/autos/gasoline-faq/part3/

Specifically:All those sources you have been reading for the last 50 years are wrong. It's an old myth. The full FAQ is attached if you want to learn more than you ever imagined about gasoline and hydrocarbon fuels. It's worth the time investment if you really want to answer the question "What fuel should I run in my car?" with the support of science. Also, FWIW, I have a turbo sizing spreadsheet that includes specifying what octane fuel you plan to use because it needs to know how much boost you can tolerate before autoignition becomes a problem (and hence detonation). More boost, more temperature in the combustion chamber from compressing the A/F mixture which also leads to why Direct Injection engines can tolerate higher static compression - fuel vaporization happens in the combustion chamber, not at the nozzle of an injector in a port or in the throttlebody of a carburetor, so the fuel's heat of vaporization allows for higher static and dynamic compression ratios with DI.

Htony

In this case we'll have to refer to design specs. for both vehicles and compare, LOL!

joindy

If you want to use 91 octane, is it best to actually do 2 seperate fills at the station....half 89 and then, new fill...with half 93 for combined octane of 91. Or is it ok just to rotate you fills.....89 one time, 93 next time. I plan do do lot of vacation travel in the GX, and may be stopping several times a day to get gas on a trip. I assume the best approach is to mix at the tank....I would think it gets mixed together quickly with driving. Most stations around here don't have 91 octane.....they have 3 grades.....87, 89, and 93. If you want to really make effort to get best price, and if 89 is lot more expensive than 87, you would do 87 -93 mix of about 30%/70%.
For those of you who do want to use 91.....and 91 is not available at the tank, what do you do?

BradTank

We only have 91 available in my state, but I always assumed when the manufacturers said "91" they meant that as the minimum octane or better (excluding something like racing fuel).

The automaker can't expect consumers to mix their gas like the way you are describing to get to 91.
I personally would just pick one and stick with it.

These vehicles are exported to all sorts of different markets and countries and all sorts of different blends with things like ethanol. All sorts of states have different formulas. I'm in the camp that believes you can pick any of the 3 octanes in the US and nothing bad will happen. You will just get peak performance from 91+ octane as the car's timing will adjust to it.

joindy

I understand your reasoning, but if I am towing a travel trailer.....for several thousand miles, I might want to make sure I have max performance, so would want to use 91 octane. I will be towing about 3500 lbs, not a heavy load for 7000 lb rating, but think you would want the peak horsepower, at least if in hill country, or high headwinds. So...that is why I am focused on trying to maintain 91 in the tank.

If I am not towing, I would agree that a 87 fill up is not going to be a problem.

So to rephrase the question, if you are towing 3500 lbs....would you try to maintain 91 in the tank, thus either mixing or rotating fills.

hzhao

I am not a chemistry expert by any stretch. But in common sense telling me, this is not mixing same solution with different concentration to make it average. 87 octane is a finished product, so as 93 octane. By mixing them, you just have a mixed product, not dissolved into each other to create new octane value. Personally, I would just using anything as 91+, but if you are really concerned saving on fuel cost, using 87 and let the engine control unit do the job to adjust timing. You will be running the car under manufacture published specification and performance value. THat's about it.

racingdc9

Using 93 will not hurt your GX. Using anything above what is required will have the same performance if not better. When I had a Camry that only required 87, after a few years I would hear some knocking under acceleration but when I put 93 in the knocking stopped. Especially, if you plan to tow, put 100% of the 93.