$ per mile: high compression/high test vs. low compression/regular

Supply and demand. My industry sources told me that during much of writing of new articles about refinery capacity shortages and oil shortages there was actually a glut of gasoline relative to other oil products.

It burns hotter,but is not worth the extra money. 87 octane is what my Dodge Van is made to run on. Its possible high test is better in the very cold. Good to put dry gas mix in to get rid of gas tank water. TreBert

Short Answer: The public is getting hosed [again]

Longer answer: A large portion of the cost difference is in taxes, in part justified in the bureaucratic mind by the extra mileage per gallon which reduces tax revenue. The rest is due to legislation requiring ultra-low sulfur which costs extra to produce using orthodox production methods.

FWIW ? ultra low sulfur and ultra low wax diesel and JP4 jet fuel can be produced by existing G/CTL [gas/ coal to liquid] technology using the abundant (cheap) shale gas as feed stock. There is two cost savings. The production cost of the ultra-low sulfur/wax fuel is cheaper than that produced by existing technology from petroleum feedstock, and it is a totally domestic product with domestic employment, eliminating a major portion of the current accounts trade deficit. Naturally, we can't do it as this might upset the major political campaign donors like the existing [tax evading] oil companies, banks, and commodity speculators, and upset the need for continuing wars in the Mid-East and Africa.

and a whole bunch more.

If your engine has a knock sensor it will slowly advance the spark until it senses knock, then back off and try again. This gives the maximum advance that the fuel, temperature, humidity and load conditions allow, and does improve the performance when you put in hi-test. You'd have to make measurements to see if the gain is worth the added cost.

Buick introduced the sensor on the 1978 Turbo V-6. The company I worked for built the test station for the sensors.

"ULSD has a lower energy content due to the heavy processing required to remove large amounts of sulfur from oil, leading to lower fuel economy. Using it requires more costly oil." jsw

It burns hotter,but is not worth the extra money. 87 octane is what my Dodge Van is made to run on. Its possible high test is better in the very cold. Good to put dry gas mix in to get rid of gas tank water. TreBert ========================================================

Dry gas, fwiw, is absolute alcohol -- or near absolute (200 proof, very hygroscopic, bad for the skin)

Heh, and a litttle known fact-let: The actual heat content of regular gas is higher than that of high test!!

So that right there may offset whatever advantages there are to high test/high compression, at least in streetable cars. The reason, btw, is due to the higher degree of branching of alkyl chains in high test, rendering a more stable carbo-cation intermediate, ergo a lower net release of energy. Organic Chem 101.

So I just added sci.chem.... haven't seen any rants from Uncle Al lately.... LOL

Yeah, anti-knock is a super-cool feature.

One can also mix regular and high test, should regular gas be outside of the engine's ability to compensate. fwiu, 89 octane is in fact just mixed 87+ high-test, approx 50/50. So an aware driver may find that for every 10 gals of fuel, 9 gal of regular + 1 gal of premium would do him good.

Correction:

The Carnot efficiency just BARELY keeps up with compression ratio, but it IS close -- or closer than I thought. But still proly futile.

Here's how it works.

Carnot Eff = 1 - Tlow/Thot Going from a compression ratio of, say, 7 to 9, gas laws will predict a temp rise of the same ratio. Using temp ratios that give an approx effic for IC engines of 67%, use 1 -

1/3. Now increase Thot by about 30% (like the CR increase), and your effic goes up to .75, for a 8% improvement in efficiency.

But, considering that, in thermo, nothing EVER turns out in your favor, it is almost a guar-own-tee that the payoff for high test does not keep up with the expense.

Combine that with the fact-let that I posted to Jim, that regular gas ALREADY has more energy content than high-test, and f'sure (well, almost f'sure) itsa losing proposition.

Along these same lines, #6 heating oil has RADICALLY more heat content than #2 heating oil, AND is substantially cheaper. So the home-moaner gets effed butt again.....

Lower octane = higher volatility, and is therefore better in cold weather. Higher octane fuel can cause hard starting.

Your engine's compression ratio is fixed and anything with an engine management system(like in the last 3 decades) is going to adapt to whatever you stick in there. Your compression ratio is designed for the lowest common denominator and the timing is adjusted automatically so it doesn't ping. My old van had a built-in mileage computer, 91 octane didn't do any better than 85. Alcohol-free gas got like 10-15% better mileage, though. Now the air-cooled VW is a different deal, only has an open-loop injection system and needs the extra octane to keep from getting holes in pistons from knock. Runs like crap with the ignition retarded.

Sulfur is the reason on the diesel, EPA decided to mandate a much lower sulfur content. Sulfur gets removed anyway in processing, just that below a certain point it starts costing a LOT extra to do. Some diesels relied on that sulfur to keep injection parts from galling and binding, I can remember guys with VW Rabbits haunting the boneyards looking for pumps after the changeover. On the other hand, you aren't breathing as much sulfuric acid in urban areas.

Stan

Your engine's compression ratio is fixed and anything with an engine management system(like in the last 3 decades) is going to adapt to whatever you stick in there. Your compression ratio is designed for the lowest common denominator and the timing is adjusted automatically so it doesn't ping. My old van had a built-in mileage computer, 91 octane didn't do any better than 85. Alcohol-free gas got like 10-15% better mileage, though. Now the air-cooled VW is a different deal, only has an open-loop injection system and needs the extra octane to keep from getting holes in pistons from knock. Runs like crap with the ignition retarded.

Sulfur is the reason on the diesel, EPA decided to mandate a much lower sulfur content. Sulfur gets removed anyway in processing, just that below a certain point it starts costing a LOT extra to do. Some diesels relied on that sulfur to keep injection parts from galling and binding, I can remember guys with VW Rabbits haunting the boneyards looking for pumps after the changeover. On the other hand, you aren't breathing as much sulfuric acid in urban areas. ========================================================

"A little sulfuric acid never killed anyone...." lol

The trick with high-octane gas is it allows the ignition to be advanced quite a bit before knocking develops. If you did that on old engines with mechanical distributors, you could actually see the difference in gas mileage. Whether it paid for the price difference was not so clear.

Today this advance could be done by the engine computer, but for the most part it WON'T, due to the increased production of nitrogen oxide.

Jon

"Jim Wilkins" wrote in news:ke4bln$5ml$1@dont- email.me:

Sorry but your not quite right. the comp will only adv the timing up to the ign map in the comp.not untill ping unless it is within the map range already. high test in an eng not rated for it will just waste the hi test because the fuel map is not optimized for the higher octaine gas. some of the newer eng with a higher comp ratio will do it but the run of the mill car will not. KB

This is quite true.

But one factor you are all forgetting is how much better the exhaust sounds on a high-compression engine vs. a similar engine with less compression :)

nate

To you, maybe. All your modern cars can't run dual glass packs

the relationship between compression ratio and octane is much more complicated than that. the japanese discovered that combustion chamber shape and its internal sonic characteristics have a significant impact on whether an engine knocks or not - it's not simply a function of compression ratio. you will therefore observe that many [modern] japanese engines go to great lengths to keep cylinder head combustion chamber features rounded, and to make sure that flame paths are as non-convoluted as possible - so they can use higher compression ratios with lower octane gas.

furthermore, not only did this engine research change compression/octane thinking, combustion chamber design has also proven to help significantly with cleaner combustion and thus emissions.

bottom line, this is a highly technical subject on which billions have been spent in research over the years. as research has advanced, old presumptions about octane and compression have had to be all but abandoned.

you're an unspeakable retard. what you're in fact hearing is the difference in the manifolds and engines that are built for higher and lower outputs. if you had two otherwise identical engines, same manifolds and exhausts, with only compression ratios different, you'd have a real hard time telling the difference. especially if you were a cloth-eared idiot with no analytic skills and even less sense about opening their mouth on a topic on which they've go no experience and even less knowledge.

To you, maybe. All your modern cars can't run dual glass packs

My only modern car can, and probably would sound good with them (likely similar to an old "Jimmy Six") as long as I don't get pulled over :)

Sadly, I'm pretty sure that glasspacks are illegal in VA. I'm sure that they are in MD; I checked.

(fires up the google machine)

§ 46.2-1049. (Effective October 1, 2012) Exhaust system in good working order.

No person shall drive and no owner of a vehicle shall permit or allow the operation of any such vehicle on a highway unless it is equipped with an exhaust system in good working order and in constant operation to prevent excessive or unusual levels of noise; provided however, that for motor vehicles, such exhaust system shall be of a type installed as standard factory equipment, or comparable to that designed for use on the particular vehicle as standard factory equipment. An exhaust system shall not be deemed to prevent excessive or unusual noise if it permits the escape of noise in excess of that permitted by the standard factory equipment exhaust system of private passenger motor vehicles or trucks of standard make.

The term "exhaust system," as used in this section, means all the parts of a vehicle through which the exhaust passes after leaving the engine block, including mufflers and other sound dissipative devices.

Chambered pipes are not an effective muffling device to prevent excessive or unusual noise, and any vehicle equipped with chambered pipes shall be deemed in violation of this section.

The provisions of this section shall not apply to converted electric vehicles.

(end quote)

So, chambered exhausts are explicitly prohibited, however, glasspacks are not - but the wording of the law is such that it is entirely likely that it's essentially at a police officer's discretion as to whether your exhaust system is too loud or not, or if he considers a glasspack to be similar enough to a factory muffler to let you go or not.

Personally, I think glasspacks would be fine on a turbo engine, but I'm obviously not the guy with the ticket book.

nate

Bullshit. I actually have experience with of what I speak. When I swapped engines in my '55 Stude - WITHOUT CHANGING MANIFOLDS, PIPES, OR MUFFLERS - I noticed a distinct difference in the "sharpness" of the exhaust note.

I swapped from a '63 or '64 model (I forget now) standard 289 which was in the car when I bought it to an engine built from a service block (but also a 63-64 casting.) The replacement engine was built to Avanti R1 spec, the main differences between the two engines being the compression ratio (8.something to 1 to 10.25:1) and slightly more aggressive cam timing. Displacement, combustion chamber shape and head port configuration, manifolds, etc. all remained either very similar or exactly identical.

Again, I did not change anything past the heads, because I'd already replaced the exhaust as part of the initial process of getting the car on the road, and the original '55 C-K body exhaust system actually used good sized pipes capable of supporting more horsepower than the original '55 engine choices put out. Studebaker actually downsized the diameter of the tailpipes for 56-64, even for the Golden Hawks and supercharged GT Hawks, so my system was actually less restrictive than the factory system on a "Super" package GT Hawk.

nate