Hi Octane fuel in regular engines 1

[bam55]

Why do they recommend hi octasne fuel in regular engines?
They say it will clean out the cylinders/carb. Others say for an engine designed for regular fuel(unleaded) it is just a waste of money. Does the higher compression engines actually burn this higher octane. How high has the compression ratio to be?

 

[MacGyverS2000]

Hi octane fuel, in and of itself, will not clean out the cylinders (AFAIK). It will, however, allow for a highr compression without knocking. If your engine is designed for low octane fuels, then yes, your money is mostly wasted by going with something of a higher octane.

Dan - Owner

http://www.Hi-TecDesigns.com

 

[Comcokid]

High octane fuel from some gasoline distributors contains higher levels of additives/cleaning agents. This is because higher compressions engines are more susceptable to knocking even with a higher octane fuel if there is any carbon buildup.

Putting a tankfull of higher octane fuel in a car may help clean deposits even if the car does not require the higher octane. But it's better and cheaper to just add a bottle of additive to your tank.

 

[patprimmer]

Bam55

There is so much hogwash about on this subject it is ridiculous.

Octane rating is the ability to prevent knock. High compression causes knock by igniting the fuel prematurely or spontaneously across the chamber instead of as a progressive flame front.

You only need just enough octane to avoid detonation or knock under the most adverse operating conditions you will encounter. Any more is wasted.

Any correlation between engine cleaning and octane rating is purely coincidental or due to other additives that may be added to support the premium claim and price. In fact, the most common octane boosters currently used in premium pump fuel are aromatic hydrocarbons and these tend to leave more carbon deposit than apathetic hydrocarbons. Alcohol is also sometimes used as an octane booster. It burns cleaner than the apathetic hydrocarbons.

The cheapest way to remove deposits is to do a power run with a fine stream of water aimed into the throttle bores. A windshield washer hose works fine. Just be careful not to run the water while the engine is not running or you risk damage from hydraulic lock.

Modern engines in good condition that are often run long enough to spend reasonable time at normal operating temperature and occasionally at highway speed, and tune run on good fuel of sufficient, but not unnecessary octane rarely if ever need cleaning.

The following links are a wealth of information on this subject.

http://blizzard.rwic.und.edu/~nordlie/cars/gasoline.html

http://naca.larc.nasa.gov/

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[evelrod]

There is so much hogwash about on this subject it is ridiculous.

Thanks, Pat. You saved me a bunch of typing. I will never understand these urban legends...how the heck do they just keeeeeeep on going and going and......

Rod

 

[TheBlacksmith]

The brilliant marketing on the part of the oil companies since I was knee high to a grasshopper of calling low octane fuel "regular" gas and high octane fuel "premium" gas. You still see this today, often times referred to as "super" unleaded.

 

[bam55]

OK Thanks,

Thats the kind of information I needed for reassurance.

Motto from this: Why make things complicated?

 

[Ataloss]

If you need proof about whether premium fuel helps clean an engine or if it helps an engine designed for low octane fuel perform better, the FTC has gone after oil companies for making these unsubstantiated claims and the oil companies could not prove their claims.

About ten years ago the FTC went after Exxon because they made unsubstantiated claims that their 'premium' high octane fuel would make the engine cleaner and reduce maintenance costs. Exxon could not prove their claims, so they had to produce ads telling customers that most cars did not require premium fuel, and unless your car specifically required it, using premium fuel would not help.

http://www.ftc.gov/opa/1996/09/exxon1.htm

Amoco agreed not to say that their premium fuel would improve engine performance or clean your engine after the FTC went after them. They agreed to this because they could not provide scientific proof about their claims.

http://www.ftc.gov/opa/1996/02/amoco.htm

Bob

 

[sreid]

I agree with everything that has been said before, but my 1999 Honda Accord definately has more wide open throttle power when using premium gas (based on "The Butt" dynomometer). I attribute this to the ping sensor not backing off the ignition advance when using premium fuel.

 

[Knap]

UK testing

http://www.thorneymotorsport.co.uk/gcs_article.php?artid=64&typelink=http://

http://www.thorneymotorsport.co.uk/gcs_article.php?type=News&subtitle=0&title=0&text=0&toc=1

may not apply to regular engines and may only benefit certain engines

My understanding with UK fuels that a few years ago the so called cheaper Supermarket fuels although same Octane used less additives compared to a branded fuel.

 

[evelrod]

I'll bet there are some of you, that should you try hard enough, could "prove" to your "butt dyno" that the "fuel magnet" will make your car run, better, faster, get better fuel mileage, etc. ad naseum! You can even buy a little stainless steel "Q-Ray" bracelet for only two payments of $49.95 that will make life "so much easier"...Sorry, the "butt dyno" won't work on this one.--- Guys, ya just gotta stick with the folks that do this stuff for a livin'. Maybe you should keep an eye out for that long lost relative that left unclaimed "millions" in an account in Nigeria.

The trouble with 'butt dynos' as I see it is 'constipation'!

Rod

 

[patprimmer]

Or more accurately the evidence of a lack of constipation in the bull pen.

Premium fuel will give more power and mileage for high compression engines with knock sensors as with lower octane fuel, the knock sensor will retard the spark to stop knock.

This has all been covered before. The inbuilt google search engine will find it for you so we do not need to go over it all again, and again and again etc etc.



Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[IceStationZebra]

One thing that hasn't been mentioned in this thread - high octane fuel is created with additives that displace gasoline with the end result less BTU/gal. Again backing up Pat - "You only need just enough octane to avoid detonation or knock under the most adverse operating conditions you will encounter. Any more is wasted."

ISZ

 

[Knap]

I thought Toluene had more energy but ethanol less.

 

[patprimmer]

I think you are correct. Ethanol definitely has less. I would expect toluene has more due to the double bonds, but my chemistry has gathered 40 years worth of dust.

I provided the link so the OP could do his own research.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[GregLocock]

No, toluene has a slightly lower calorific value than gasoline, by weight, but is much denser, so by volume it has a higher energy content. The main contributor to CV is the hydrogen, all the carbon really does is provide a good way of storing hydrogen. That's why the shorter hydrocarbons have higher CVs. Toluene 'wastes' links by double bonding to carbon, rather than storing more hydrogen.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Knap]

I understand that fuels sold in UK except Shell Optimax (V power) Tesco 99 (Ethanol) and perhaps BP Ultimate (noticed run on using this), are basically and often literally, exactly the same base product in to which each company puts in their own additive package. i.e you will see all kinds of tankers filling up at a Shell distribution site, Texaco, Esso, BP, Sainsburys, Tesco etc. etc. and they all fill up with exactly the same base fuel, i.e. they all share distribution points in order to reduced transport costs, but each company will add its own additive package at the filling gantry. Whether some additive packages are as good as others may be debatable!

I understand that Optimax is produced from a completely different base product than all other gasoline products available. The base fuel used is more highly refined than normal gasoline, hence the superior performance. Also the additive package used amongst other things is extremely effective in cleaning the engine inlet tract and combustion chambers. When used in engines that have previously only used "normal" gasoline, Optimax cleans these components to an as new condition!

Optimax was also subject to "overadvertising" but the claim was not upheld effective detergent additive,

http://www.asa.org.uk/asa/adjudications/non_broadcast/Adjudication+Details.htm?adjudication_id=37402

An additional advantage is that, due to their different composition, "premium" fuels are typically two or three percent more dense than "normal" fuel, which means that each litre contains two or three percent more mass of fuel, and hence two or three percent more energy. All other things being equal, that automatically translates into a two or three percent improvement in fuel consumption (miles/gallon or litres/100 km).

http://fuelsaving.info/fuels.htm

I also understand Optimax to use Toluene in their fuel

Toluene is denser than ordinary gasoline (0.87 g/mL vs. 0.72-0.74) and contains more energy per unit volume.

http://www.elektro.com/~audi/audi/toluene.html

The other additive that is being advertised with Texaco fuel in Ireland is Techron

http://www.chevron.com/products/prodserv/fuels/techrongas/

Then with the Dyno testing the Tesco 99 Ethanol fuel produced the goods.

Perhaps a grain of truth but not value for money?

 

[evelrod]

An additional advantage is that, due to their different composition, "premium" fuels are typically two or three percent more dense than "normal" fuel, which means that each litre contains two or three percent more mass of fuel, and hence two or three percent more energy. All other things being equal, that automatically translates into a two or three percent improvement in fuel consumption (miles/gallon or litres/100 km).

Hmmmmmmmmm?

Rod

 

[patprimmer]

It is more likely to translate to 2 to 3% rich mixture unless the fuel metering system corrects at that level.

Carbies certainly won't EFI mostly will in increments of a size I don't know, but I am sure someone else here will know.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[evelrod]

Well, since I'm sorta 'anal' about this...and mostly to the OP's original question...

2001 Lincoln LS V6 purchased new March 20, 2001.

Premium or 91 octane recommended by OEM and used from March 2001 until May, 2002---
Regular or 87 octane used from May, 2002 until present---

106 miles daily during the week for 90% of the cars life (wife's car, to work and back, now at something near 145,000 miles and counting, still on OEM sparkplugs and just passed it's first mandated California smog check)---
Fuel mileage has NEVER varied outside the min/max of 21/22 mpg...EVER! I've kept track of lots of my cars in the last 49 years and have never documented notable variations in fuel mileage using "premium" v "regular", carbureated or fuel injected, supercharged/turbocharged, automatic/manual trans, unless the engine in question was modified to the point where "regular" could not be used under any conditions. This is "strictly street" stuff and, obviously does not include my race engines or cars which typically use ~110 octane race fuel.

There are obviously some caveats in this statement...In the '60's "premium" could be as high as 100+octane and regular could be as low as 62 octane (depending on where you were in North America)...Some of the Detroit offerings had high compression engines that just barely operated on "premium", granted...That is not the point, that was 'then' this is 'now'. I'm just gonna need a lot more "documentation" before I just sign off on another "urban legend". 2%---3%---sorry, I need more
than casual 'guesstamation'!

Rod