Is there an advantage?

[Boondocker]

Originally Posted by Wabbiteer

Towing my AS at 55mph and smooth higway driving gave me almost 14mpg using premium - I started calculating dollars per mile and saw a spread between $11 to $17 dollars per hour cruise with speeds & fuel octane changes. Hate being an obstacle in the right lane but money is too tight to be fuelish, just smile and wave like its great fun and get even at the fuel pump.
~

Hmmm. First trip with the Trade Wind I got about 8 mpg. Reading here I found out that 5th (or overdrive) is not my friend. Going to the midwest forums rally I kept it in 4th and right at 55 traveling mainly on state routes. Result: about 11-11.5mpg. If switching to premium would give some more power and boost me another 1-2 mpg, I would be a happy camper indeed.

[bhayden]

Originally Posted by Gen Disarray

Does anybody know of a state by state break down of ethanol additives? or has it become ubiquitious now?

In Washington it varies by region. The Seattle area has the worst polution problem because of traffic density and the trapping of air between the Olympic and Cascade mountains. When we go on trips and fill up "out in the boonies" I regularly see 2mph increase (10%) over fuel in the Seattle area. The huge difference in efficiency makes me wonder if the added ethanol might actually increase polution.

Modern cars adjust the timing and fuel mixture based on the exhaust gas. OBDII cars don't even get "tested" when you take them in for emissions. They just hook it up to the computer and the car tells them how it's running. My old '86 Crown Vic that was originally a State Patrol car hates regular gas. The combo of dumb engine management and slightly higher compression makes it ping like crazy. That will destroy an engine in short order.

Aviation fuel has long been used by hot rodders and racers. Even with no road tax it commands a steep price premium.

-Bernie

[uwe]

Originally Posted by safari57

My wife's BMW 740I gets 3 to 4 MPG better when running premium versus lower octane fuel. It is noticeable over a long journey although the actual costs incurred are up due to the use of the more expensive fuel. We do notice that the car "seems" to run better with the higher octane but that could just be me.

Barry

Barry,

The 740I runs Motronic by Bosch, a truly adaptive engine management system. It occupies sensors for many different engine and ambient parameters. This vehicle does benefit from high grade fuel, as it will advance timing of spark plugs and injection depending on the sensor's inputs many times a second. The result is usually a smoother running engine, that has a crisper throttle response.
My 1997 Suburban is supposed to have a knock sensor, retarding timing to prevent engine knock under load when running regular unleaded gas. I have had the vehicle at Chevrolet several times, because there is a pronounced engine ping under heavy load when towing. This goes away when I run premium unleaded. Chevrolet says that there is no fault in my engine management system, and everything is as it is supposed to be. But still, I must run premium when towing, while it motors along quite happily on regular when not towing. However, there is no difference in mileage, or otherwise, when I run premium while not towing.

[Bob Thompson]

Has anyone ever seen an engine that was destroyed by pinging? I keep hearing that pinging will destroy an engine in short order, but I never have seen one damaged in that way and would enjoy finding out what parts were damaged (in short order). Diesels work on the principle of predetonation and without it they wouldn't even run. Someone Please, show me pictures of a gas engine destroyed by predetonation knock. I want to see the bearings which were pounded flat, or the pistons with big holes burned in them, maybe a split or cracked valve or valve seat. Inquiring minds want to know (and see).

Personally, I think this was a phenomena which was seen prior to 1950 when engine parts and lubrication wasn't up to the very high standards we see today, but then I may be wrong. Predetonation could have lead to the demise of the Hudson, the Studebaker, the Oldsmobile or the Yugo. We need to see what we are so afraid of!

We need John Stossel set up two engines side by side on dynomometers, one set to ping and one not and run them until one fails and look at what happened. Also, it sound like a good test for "Myth Busters".

[jcanavera]

Originally Posted by Bob Thompson

Has anyone ever seen an engine that was destroyed by pinging? I keep hearing that pinging will destroy an engine in short order, but I never have seen one damaged in that way and would enjoy finding out what parts were damaged (in short order). Diesels work on the principle of predetonation and without it they wouldn't even run.

I'm far from being a mechanic but I was told that in a gas engine, the spark is fired just prior to the piston being at top of cylinder. By the time the force of ignition occurs the piston is at top and no damage occurs. It's all in the timing of the spark and the position of the piston in the cylinder. Spark or ignition comes too soon, and you get the effect of the explosion occurring and attempting to force the piston down, when in effect it is still on the upstroke. I've attached a picture of a damaged piston where preignition occurred.

Someone correct me if I'm wrong but doesn't the compression in a diesel engine actually trigger the ignition? I would think that the diesel would work on the same principal, minus the ignition spark. Its a high compression engine which generates the heat at high compression. The piston again would be almost at top when the explosion occurs. Obviously the glow coil provides the initial heat source until the engine heat is self sufficient to maintain the combustion.

Jack

[uwe]

Originally Posted by Bob Thompson

Has anyone ever seen an engine that was destroyed by pinging? I keep hearing that pinging will destroy an engine in short order, but I never have seen one damaged in that way and would enjoy finding out what parts were damaged (in short order). Diesels work on the principle of predetonation and without it they wouldn't even run. Someone Please, show me pictures of a gas engine destroyed by predetonation knock. I want to see the bearings which were pounded flat, or the pistons with big holes burned in them, maybe a split or cracked valve or valve seat. Inquiring minds want to know (and see).

Personally, I think this was a phenomena which was seen prior to 1950 when engine parts and lubrication wasn't up to the very high standards we see today, but then I may be wrong. Predetonation could have lead to the demise of the Hudson, the Studebaker, the Oldsmobile or the Yugo. We need to see what we are so afraid of!

We need John Stossel set up two engines side by side on dynomometers, one set to ping and one not and run them until one fails and look at what happened. Also, it sound like a good test for "Myth Busters".

I like the myth buster idea, Bob. They have the funds to pull of these things..and cameras!
I am amidst a engine rebuild on a 59 Mercedes 6-cyl. This engine has had it's share of pinging and clattering, and tehr eare no signs of damage on teh piston tops, or valves, or valve seas. Just normal wear.
A while back ( quite a while) I drove a 79 Buick "ping" Estate wagon..for a hundred thousand miles or so, the thing pinging just about all the time. It would run on after the key was off, like in a bad movie. It did not break for me, unfortunately. We eventually junked it because of other reasons.
So, I second your question on the real problem with engine ping.
My Suburban pings at certain times, as described in another post. My impression is that when the pinging starts, the perceived engine power drops a bit. But what else is happening?

[Bob Thompson]

I did study Mechanical Engineering in College and one of the areas we studied was fuels, anti-knock compounds, and internal combustion engines. Based on the principle that compressing a gas causes it to heat to the point of combustion is what we're talking about. Diesels are based on this principle. Compression ratios of around 17:1 are required to get diesels to fire. A ping, or predetonation knock is the fuel firing because of compression. By adding anti-knock compounds, this firing can be delayed until the spark of the spark plug fires the fuel.

I do see some damage to the top of the piston, but it is in the form of scratches, gouges, etc. Since there is no way a piston ring could have caused this damage, it had to have been a valve or a foreign object which caused the damage. I've looked close and don't see damage caused by preignition. Perhaps someone can point out this damage for me. Are there minute stress cracks in the top of the piston which I can't see?

I have seen pistons with holes burned in them from running too lean and too hot, usually because of supercharging or turbo'ing. This is a case where someone has added an aftermarket device to artificially boost the compression ratio but didn't recognize the need to boost the amount of fuel to the cylinder so that the fuel air ratio was maintained at the correct proportion.

Our family had one of those vehicles which ran on after the ignition was turned off. It would set there and run and run and ping and knock and send out black smoke, and you just knew it couldn't be good. But the engine, like Uwe's lasted well past 130,000 miles, and it was other problems which eventually lead to it's end.

[Boondocker]

Does anybody know where to find a state by state (or by region) listing of ethanol added gas? Or is it just everywhere now?
thanks

[GlenCoombe]

Fuel saving myths abound...but somewhere in the back of my collective consiousness I recall that premium (ie. higher octane) fuels burn longer than their regular counterparts.
This longer burn results in more BTU's and more complete combustion. The end result could be a modest fuel economy boost but the more important factor is reduced emission of unburned fuel.
I'm just glad Airstream One lives on regular fuel. The cost of premium would have me in the poor house.

[TIMEMACHINE]

In general I usually go with the vehicle manufacturers recommended fuel.....BUT....I also may downgrade if the engine does not knock or ping under load with a lower grade gasoline.

If you go to the auto forums you will get 180 degree answers from the pros. So who knows for sure, I think it is a matter of individual circumstances including engine type, terrain, driving style, etc.

[Boondocker]

Using todays prices, if using non-ethanol (premium) gas resulted in a 12% increase in milage the price per mile is a wash, a 20% improvement (which is often claimed) would save $1.94 per 100 miles, or about 2 cents per mile improvement. Doesnt sound like much at first glance, however, given a 4,000 mile trip this is just over $75. Even a 15% (likely as I read) increase in milage would give you about a penny an mile boost. So I guess the smart money is on watching the split between regular and premium gas.

[j54mark]

Lots of information here, but it seems to be scattered in such a way as to be confusing.

"Compression ratio" is the ratio of the compressed gasses at top dead center of the piston travel expressed as the ratio between the compressed gasses and normal atmospheric pressure. Theoretically, it is possible to get more performance out of an engine with higher compression, which is why most Porsche, Audi, Mercedes, BMW, Corvette, and other high performance cars specify higher octane fuel. At higher altitudes (Denver), normal air density is lower to start with and so the compression ends up lower as well, allowing the use of lower octane than would be necessary at sea level - but also producing lower power.

Octane is a rating system which describes a fuel’s propensity to ignite under pressure. The higher the number, the higher the compression ratio can be before spontaneous ignition. The BTU content of 87 octane is the same as 92 octane, but as noted above, it is possible to get more power out of the higher octane gas by compressing it more before ignition. On the other hand, unless you have an engine with enough compression to take advantage of it, higher octane will do no good at all.

As noted in other posts, fuel with 10% ethanol will have a lower btu than straight gasoline, so premium gasoline without ethanol will likely produce better milage than ethanol/gasoline blends, not because of the octane, but simply because more btu's are available.

The compression ratio of an engine does not necessarily stay constant over time. In the old days engines routinely accumulated enough combustion by-products in the cylinder head to significantly increase the compression ratio. So it was common for 50's and 60's cars to need premium gas after 60,000 miles or so, unless the heads were "decarbonized". With the cleaner burning fuels of today this happens much more slowly, if at all.

"Pinging", or "knock" is the spontaneous ignition of the fuel/air mixture prior to the firing of the spark plug. This means that the affected piston is forced to further compress expanding gases. Since the piston cannot actually move backwards against the other cylinders in the engine the pressure forces inside that cylinder become many times higher than the design parameters. A blown head gasket, broken wrist pin, broken piston, cracked head, cracked cylinder liner, broken block, deformed rod bearings, or broken rod are all possible. Severe knock will wreck an engine in minutes, but the light, occasional "pinging" most of us are familiar with will merely reduce the engine life from, say, 300,000 miles to only 175,000 miles.

A hot engine will knock more readily than a cooler one. This is why it sometimes occurs while towing, but not in ordinary driving.

Mark

[Boondocker]

Originally Posted by j54mark

Lots of information here, but it seems to be scattered in such a way as to be confusing.
Mark

To recap. The question was if there was an advantage to using premium gas.

As I follow the main points....

The issues are two:
1) Higher octane does not help, unless your vehicle is designed for it, in which case you need to be using it anyway.
2) One important difference between the fuel grades is that non-premium gas often has 10% ethanol which does reduce performance. The sub issue is how much performance you loose and how wide the gap in prices between regular and premium is in order to justify the added price for improved performance.

Does this sum up things to this point?

[bhayden]

Boy what a complicated mess. It was news to me that Premium might not contain Ethanol. Time to start looking more closely at the lables on the pump. I know some say something about "may" contain up to 10% ethanol and others say something like "oxygenated gasoline" (bubbly )

I knew it was a mess with different States and different regions in parts of States requiring certain blends depending on time of year. I didn't know about some of the problems associated with Ethanol besides lack of performance and the unintended environmental damage done by some of the other laws. Interesting read:

http://www.sfgate.com/cgi-bin/articl...AG04H9IQG1.DTL

It's so hard to separate the politics from the science:

8/15/2003 Gov. Gray Davis is renewing his push to eliminate ethanol as a federally mandated clean-air additive to California gasoline. But the embattled governor's prospects of persuading the Bush administration to reverse itself - a move that would disappoint the president's Midwestern supporters who have their eyes on a new market for their corn product - may be no better than of surviving the Oct. 7 recall election.


Could it be we're replacing "Big Oil" with "Big Corn"


I still haven't been able to find out if the drop in milage compensates for the "cleaner" emissions. In Washington it's all based on % of gas in the exhaust but if you're burning more fuel per mile then the total volume (and mass) of you're exhaust is greater.


Corn-fused,
-Bernie

[Chuck]

Originally Posted by j54mark

Octane is a rating system which describes a fuel’s propensity to ignite under pressure. The higher the number, the higher the compression ratio can be before spontaneous ignition. The BTU content of 87 octane is the same as 92 octane, but as noted above, it is possible to get more power out of the higher octane gas by compressing it more before ignition. On the other hand, unless you have an engine with enough compression to take advantage of it, higher octane will do no good at all.

but the aftermarket chip reprogrammers claim to boost performance...some, only with the use of premium. another one claims "some" gains w/ regular, but more w/ premium. what's up w/ that?

Originally Posted by j54mark

As noted in other posts, fuel with 10% ethanol will have a lower btu than straight gasoline, so premium gasoline without ethanol will likely produce better milage than ethanol/gasoline blends, not because of the octane, but simply because more btu's are available.

I've been watching since they made the 10% ethanol change here. On my first tank in the truck, I recorded among the highest mpg I've ever clocked. Haven't had the chance to re-check, because I don't have the truck most of the time (the mrs. uses it as her daily-driver...I take the car on the 32 mile commute to save gas). The car does not seem to have been negatively impacted, either, coming in at 26mpg last check. no particular effort to drive conservatively on my part, either. In the past, I've clocked a maximum of 27, but only when really trying (i.e. keeping it below 65mph).

Originally Posted by j54mark

The compression ratio of an engine does not necessarily stay constant over time. In the old days engines routinely accumulated enough combustion by-products in the cylinder head to significantly increase the compression ratio. So it was common for 50's and 60's cars to need premium gas after 60,000 miles or so, unless the heads were "decarbonized". With the cleaner burning fuels of today this happens much more slowly, if at all.

well...the last Taurus I had started pinging at 60-70k miles. "mid-grade" would stop it. The present Taurus is also starting to ping slightly under acceleration (80k). I really don't want to upgrade the gas at these prices, though. wish there were something else I could do....

[Wabbiteer]

Be aware that a 'new' ethanol blend often is only replacing an old MTBE ether oxygenator cocktail, when I lived in Washington DC area they changed to oxygenator blends to reduce summer smog and our vehicles would promptly loose 8-12% milage on the switch over... So what was being sold before ethanol that gave such lousy milage? No matter what, ethanol won't provide same energy as petroleum and has to use more for same output...

I am tempted to add 2 or 3% diesel to each tank just to try compensating for the ethanol here in Minnesota. Back east the no-name gas station with best price always has product that smells like diesel, comes from a tank farm in the Port of Baltimore and maybe a by-product of cleaning tankers or piplelines but gives good mileage when I am there.

I pulled this off a late friends' photo gallery.. Thanks BobN



~

[j54mark]

Originally Posted by chuck

but the aftermarket chip reprogrammers claim to boost performance...some, only with the use of premium. another one claims "some" gains w/ regular, but more w/ premium. what's up w/ that?

It would seem that some of the chip makers boost performance by the time-honored method of advancing the timing. And it can work. Ford sales would drop like a stone if all of a sudden you had to use premium in their family cars, so they calibrate them to run smoothly on regular.

There are a lot of factors involved. Car sized automatic transmissions and radiators can only handle so much heat, so some engines are deliberately de-tuned accordingly. Yes, your Chevy Duramax CAN make 500 hp.; but your radiator can't cool it - there is a reason why the grilles in medium duty trucks are so large.

There are pollution issues as well, which is why people frequently (but not always) must replace their hot rod chip with the factory one to pass an emissions test.

Mark

[Bob Thompson]

Some of the replacement chips only trick the throttle position sensor into believing it is open wider than it really is. Result: the fuel injectors shoot more fuel into the cylinder, voila.....more horsepower. Downside...gas mileage takes a hit. I'm saying "SOME" not "all". You can save the price of the chip by pushing your gas pedal down farther! Some miracle cures aren't!

[bhayden]

Diesel in with your gas to improve performance? I've never heard that trick before. If it works I'd still be very leary of what it would do to platinum plugs, catalytic converters, fuel injectors, etc. Don't diesels all run fairly extensive fuel filtering systems? I know someone that got diesel in his MG gas tank once and it was an expesive repair. I don't think it'll mix completely with the gas but rather sink to the bottom risking an expensive repair.

-Bernie

[SilverToy]

Also heard of EXTENSIVE and EXPENSIVE repairs associated with diesel into a gas motor. ANY. Period.

There are MORE THAN ENOUGH other additives you can buy/ add or otherwise aquire that will boost octane, and prevent knock.

Of course, if you add up the 'per tank' cost of the additives, higher octane gas still is cheaper.... Just using MY calculator though..... Your math may vary.

Use the proper (manufacturor indicated) octene gas and all will be well, you will likely get the indicated mileage (or close depending on your right foot), and you will get loads of miles out of the vehicle....

The vehicles built these days are WAY better than those built years ago.

That is NOT to say that the oldies aren't goodies, but then they have learned a thing or a zillion in the interem....

Get the gas rated for your TV and you'll be "a happy camper".....

What more can we ask for???

Axel