Another Word About Octane

[SacramentoMike]

NEPRT-bound? Possibly, but I think it's interesting anyway, and maybe even useful. And this question has popped up pretty regularly over my time here on the forum.

My local paper carries a weekly column called "Car Talk" that gives good straight answers to readers' car-type questions, usually with good humor. Today's question was on what grade of gasoline "Dee" should put in her Lexus--she thought it was good to "treat" it to premium gas once in a while. I liked the reply:

"People mistakenly think of gasoline grades as 'good, better, best.' That's because gasoline companies have done a masterful job of marketing. By calling the highter-octane fuels 'Premium,' they've convinced people that higher octane is somehow better. It's not.

"Instead, think of octane like your shoe size. If you wear a size 9, would you buy a size 13 because it has a higher number and therefore, has to be better? Of course not. You'd end up with blisters. And maybe get some extra money by working as a birthday party clown.

"The octane rating is a measure of the temperature at which the fuel will detonate inside the cylinder. Every engine is designed to be used with fuel of a specific octane.

"You don't want fuel with a lower octane than is required (because you can get pinging, pr pre-ignition, which can damage the engine), but you don't want fuel with a higher octane either (because you'll be throwing away your money). And since Lexus (read: "Yamaha") says in the owner's manual that your car is designed to run on 87-octane fuel, that's what you should get.

"In the old days you used to hear that using higher-octane fuel had all kinds of beneficial properties: it would clean out your carburetor, it would remove carbon from your pistons, it contained special detergents to clean your fuel injectors, it would regrow hair.

"All of those are false. Cars don't have carburetors anymore. Carbon doesn't build up on pistons. And fuels of all grades contain detergents.

"Save your money, Dee. Buy the grade of fuel recommended by your manufacturer, and wear the right size shoe, too."

 

[Mr_Canoehead]

Gotta love 'Click and Clack, the Tappet Brothers'. Who would have thought that a car repair show could be so funny (and informative)? My father, who has no interest in cars (or motorcycles) tunes in every week.

https://www.cartalk.com/content/premium-vs-regular-0

I love putting regular in my FJR, my other bikes (and SWMBO's car) all require premium. Here in Canuckistan, premium costs up to $0.20/liter more than regular (about $0.75/US gallon more), and I always wonder how much regular I got from the last guy before the premium cleans out the hose.

 

[Fred W]

While it is no longer true, there was a time that varying grades of fuel did have different additive packages in addition to the ones that increase octane. That is what's behind some of these misconceptions of "Premium" being better fuel.

The analogy of shoe sizes to fuel octane is a specious one since having too large of a shoe is equally as bad as having one too small, but the only downside to buying higher octane fuel than the minimum required is that it is a waste of money. It is also pretty rare for a shoe manufacturer to charge the consumer more for larger sizes, or to subconsciously promote the idea that bigger shoes are the "premium" ones.

Now, something else to consider is: Why does "Premium" cost so much more than "Regular" gas if the base gasoline and detergent additives are essentially the same? Is it the additive that boosts octane that is so expensive? Not really. The additiives are not all that expensive and the volume per gallon is pretty small. It's more about supply and demand. More vehicles than ever are requiring higher octane, and the refining industry has not kept pace with the demand. Decreasing supply and increasing demand always means higher prices.

Glad I can pump good ole' regular into my FJR, Vstrom, my truck, and my wife's car.

 

[08FJR4ME]

I remember when it was only a nickel between grades. Then it was ten cents for a while. Now it is at least 20 Cents between grades. Are they screwing us thinking we would never notice? Part of the problem to me is the youngen's don't carry cash anymore. This tells me they don't know the value of a dollar. Just swipe you young idiots and play the game the way we set it up for you. Doesn't anyone see what's going on these days.

Rant off,

Dave

 

[Fred W]

Many parts of the country the "premium for premium" is up around 50 cents a gallon. As I said, it is not because of the cost to produce the fuel. It is strictly a supply and demand thing. So having vehicles that do not demand high octane keeps you in good supply!

 

[900gc]

Back when I had my '98 E38 (740il) BMW, I attended a performance workshop hosted by tuner Steve Dinan. The E38 was tuned to require 91 octane but he said that the ECU would compensate for higher octane and would increase HP and torque a small amount with 93 or 94. I went to other way and ran 89 which I imagine knocked back the tune a bit to prevent pre-ignition. Honestly, if the difference in octane grades would technically show on a dyno graph, I couldn't tell the difference between 89 and 94 performance wise in every day driving .

My SV race bike has 2mm over, 14 to 1 compression ratio pistons so it needs 98 or so octane, I have to laugh at track days when guys pull up to the Sunoco race gas pump for their $8 gal. waste of money fuel in their stock street bikes.

 

[Old Guy]

Many years ago we had a 6-cylinder Ford, and the dealer told us to run "Premium" only. At the time I did all the fuel purchases and just drove the car to a gas station two blocks away on Saturday mornings, and my wife was never with me. I just continued to run "Regular" and never told my wife any different.

Then one day a buddy and I were working on his bike in my garage when she returned from a shopping trip. She passed through the garage and said "That car runs so much better since we started using premium in it." I gave him a look that indicated he should just be quiet, but I could tell he was about to lose it.

I do like it on group rides when most of the riders use "Premium" There's not such a line at my gas pump.

 

[Fred W]

Back when I had my '98 E38 (740il) BMW, I attended a performance workshop hosted by tuner Steve Dinan. The E38 was tuned to require 91 octane but he said that the ECU would compensate for higher octane and would increase HP and torque a small amount with 93 or 94. I went to other way and ran 89 which I imagine knocked back the tune a bit to prevent pre-ignition. Honestly, if the difference in octane grades would technically show on a dyno graph, I couldn't tell the difference between 89 and 94 performance wise in every day driving . My SV race bike has 2mm over, 14 to 1 compression ratio pistons so it needs 98 or so octane, I have to laugh at track days when guys pull up to the Sunoco race gas pump for their $8 gal. waste of money fuel in their stock street bikes.

I used to own a few BMW cars back when they were the ultimate driving machines. Now it is more of a slogan than any big difference. I had an E34 with the 5.0 V8 and an E36 with the silky smooth 2.5 inline 6, and even a little Z3 with the 2.8 six. That little guy would move out.
I remember that there was always a great deal of confusion about what the octane requirements were for all BMWs at the time because they specified 91 octane in the owners manuals, but it was by the MON scale, which was more widely used in Europe at the time, vs. North American pump octane, which is RON + MON / 2. Fuel that is rated 91 MON is roughly equivalent to regular 89 pump octane in the US, but many owners still insisted on running Premium anyway. Because the timing was not variable on those cars there was no advantage to doing that.

OTOH, I have always been a big fan of turbocharged engines in cars, which incidentally is the new power plant approach at BMW these days. I've owned several different SAABs with high output turbo 4 cylinders over the years, and my wife still drives a 2003 9-3 Vector. And my current truck is an F150 with the Ecoboost 6.

Turbos provide the fuel efficiency of a smaller engine displacement when dawdling along, but the torque and power of a much larger one when you mash the go pedal. It also provides the ability to run various fuel grades (octane) and will actually provide more potential power when running higher octane fuel by increasing intake boost, and thereby increasing effective compression ratio on the fly. So for droning along on the highway you can run cheaper low octane fuel, but if you want to bust out the ponies you can splurge on higher octane and the ECU will relearn when preignition starts and increase the allowable boost before the waste gate opens.

The difference in power can be huge when you custom program the ECU, at which point you can increase the boost to the point of grenading the engine. But it will make a lot of power before it does.

 

[mech 1 twa]

Most or all newer vehicles have a knock sensor, this sensor can hear or feel preignition from too low an octane.

If it detects knock it will retard timing and or boost reducing power until it goes away. Engine will make more power if timing and boost are not retarded.

I like driving turbo vehicles, just a little soft off the bottom until boost comes in. Much better these days than in 80's. Lag is smoother.

I see so many that are burning oil though.

Turbos like a little cool down before shutting down engine and good oil.

You can make big power from a small engine with a turbo. 450 hp 2.0L 4 cyl. BUT it needs to be dyno tuned.

 

[Fred W]

Retarding or advancing ignition timing doesn't do much. If the compression ratio is low enough to run low octane fuel there really isn't much you can do to milk more power out of the fuel charge, unless there is forced induction. The vast majority of internal combustion engines produced today are still naturally aspirated. Some manufacturers are advancing ignition and valve timing for higher rpm power, but that doesn't improve torque, only horsepower by running at higher revs.

 

[El Toro]

Our price for E10 is about two bucks a gallon these days. And that's even with our new increased gas tax that went into force on July 1st.

I use real gasoline in the bikes. No Ethanol. E0.

Today before my ride I filled up. Usually the difference from grade to grade is more than it was today. Today it was a dime.

I don't buy motorcycle gasoline on price. I buy E0, and pay the premium to get it. I buy E0 because sometimes any given bike can sit for several weeks in the garage while I'm choosing to ride others.

So today the three grades of E0 were priced at $2.59, $2.69, and $2.79.

I sprung for the 93 octane. Did it matter? Probably not. But my gas mileage on today's trip (fill up at start and full fill up again at end to same level) was 20% higher than normal. I was quite surprised. I was not particularly well behaved, with the speedo sitting at 80 mph and above for most of the trip, and with bursts for passing as high as 100 mph. I was expecting to have lower than usual gas mileage.

 

[SLK50]

All my vehicles get 87 octane, ethanol laced, regular gas.

Some only get run 2 or 3 times a year.

Most sit all winter without any treatment.

Shockingly , they all start up and run. Every time.

 

[mech 1 twa]

Timing does have a huge affect on power. As RPM's increase it needs to change because piston speed increases. To late and charge won't be ignited at proper time.

Old engines had weights inside distributor to compensate as RPM's increased. New FI systems use whatever the ECU is programed to do. An engine that idles at 1100 RPM and revs to 10.5. timing does change.

Smaller piston are less prone to preigition than large ones. There are many variables valve lift, duration, static compression ratio, combustion chamber shape and size.

E0 is hard to find in PA. A few stations but its more $$$.

I was in Altoona last fall. Good roads Big woods.

 

[Fred W]

My point was that varying ignition timing doesn't do much to reduce preignition once conditions are ripe for that. Otherwise nobody would need high octane fuel. The knocking is caused by the fuel charge igniting before the piston reaches TDC because the fuel volatility is too high for the temperature and compression of the charge. That's why they call it preignition. It explodes before the spark even happens.

 

[El Toro]

There's a reason this theead's in NEPRT.

Imagine how high some of our post counts would be if NEPRT posts were added to our counts .

 

[deagle]

Good post SacrementoMike. I KNOW I'm supposed to run 87 in my FJR. For years Premium was only 20 cents a gallon more, and that's what I used. Now Premium is like 70 cents a gallon more. Mid-grade about 25 cents a gallon more. I know the FJR runs just fine on regular. But then I read (paraphrasing) "if knocking occurs put in a higher octane gasoline". What? It may knock? Then on my SUV and my wife's SUV the manual states either (paraphrasing) "regular octane ok, but premium recommended for better performance", or "when towing use a higher octane gasoline". Honda Pilot and Nissan Murano, so neither high performing vehicles. Things like that sure make it seem like there is a benefit to putting in the "good stuff".

 

[art miller]

There you have it!! SacMike introduced the topic and summed it up all in one post. After 15 more comments we have concluded the same.

 

[SacramentoMike]

After 15 more comments we have concluded the same.

One hopes.

 

[Fred W]

Oh, I see... This was not intended to be a forum for discussions; just a place to display your own opinions with no discourse.

In that case they should just disable the ability to reply. That would make things much simpler.