low octane/cheap gas
06-11-2011, 11:59 AM
#31
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Not true. Low octane burns longer, that's why engines run hotter due to more time spent with burn happening in the combustion chamber.
06-11-2011, 12:23 PM
#32
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I've run 87 in my 89 since I've owned it; that is, when it did not have a suypercharger. When it did, I ran 91. Anyway, it does not knock and anybody that has ridden with me knows I am not gentle on the throttle. Sharktuner monitoring has not shown any knocking on 87. Now that the supercharger is gone, I'm back to 87. Unless you have knocking, there's no reason to use higher octane.
So if Sharktuner is not picking up any knock-retards with 87 octane then there is enough margin with compression and ignition timing, to avoid any detonation.
The question then is this: If you used higher-octane (slower-burning) fuel and didn't change ignition timing, would you get less horsepower? (Or lower efficiency at highway speeds, i.e. lower mileage?).
My thinking here is that, for a given engine RPM and load, ignition timing is ideally adjusted to maximize the efficiency of the engine-- max HP at that operating point. Because combustion takes some time (depending on temperature, pressure and octane), the spark starts the combustion early, before the piston is at TDC. If the fuel burns too fast, and the pressure/temperature gets above a critical point while the piston is still traveling upwards (and compressing the mixture) and detonation results.
And there will also be less power, because the piston is pushing against the increasing pressure, rather than being pushed by it. The fix here is to reduce the ignition advance, and light the fire later because it is going to burn faster.
And conversely, if the fuel burns more slowly (i.e. higher octane), then the maximum pressure will occur later, and some of the power will be lost because the piston is beyond the optimum point as the combustion pressure increases.
If this is correct, then I would think that running a higher-than-needed octane would actually result in less HP, unless the ignition advance were also adjusted.
So here is what has me really scratching my head: If you take an engine which is happy on 87 octane (i.e. no detectable detonation), and switch to 91 octane and also advance the timing by whatever is appropriate (a few degrees?), does that result in a net increase in power? Or is the result the same as 87 octane and original timing?
Cheers,
06-11-2011, 01:24 PM
#33
Burning Brakes
Barry , all the fuels in B. C. contain upto 10% ethenol . that means more deposits and less power . I run only 94 octane its all dino fuel . Good gas is the cheepest part of running a car IMHO Terry
06-11-2011, 02:01 PM
#34
The octane molecule C8 H18 is the standard used in percent volume of petrol. It's deflagration rate is higher than longer chain hydrocarbons and vice-versa. Unless you know 100% exactly what your fuel is comprised of and the various molecules with their corresponding burn rates, you're left having to trust what the pump states. That being said, if you did an analysis (HPLC) of the various brands, say 91 octane, you'd find differences in the octane percentage from pump to pump.
06-13-2011, 11:57 AM
#35
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that's so true, it's not like i want to save money on gas, i just don't want to waste money that's when i didn't know all the differences until now, i am almost empty so back to 91 it goes, thanks all
06-13-2011, 02:49 PM
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Read this article and note the comments even from a Porsche Engineer....."By James R. Healey, USA TODAY
Marti Mayne once fueled her low-octane Subaru with high-octane gas. Not now. Premium-gas prices "went sky high, and now I just use low grade" to motor around Yarmouth, Maine, where she runs a marketing business.
Cost differences between regular and premium is as plain as, well, the sign at the station, like this one in Chicago.
By Scott Olson, Getty Images
When prices dropped earlier this year, she stuck with cheaper fuel because "I don't think that my car runs any differently on high, medium or lower grade."
She's right. Engines designed for regular fuel don't improve on premium and sometimes run worse. And today's engines designed for premium run fine on regular, too, their makers say, though power declines slightly. (Background: About Octane ratings)
But premium lovers are passionate. "I would simply curtail driving rather than switch grades," says Bill Teater of Mount Vernon, Ohio, who puts high-test in both his Cadillacs, though only one recommends it. He's sure both the DeVille and the Escalade run rough and lack pep on regular.
Prejudice and preference aside, engineers, scientists and the federal government say there's little need for premium.
When fuel's cheap, motorists are willing to pay 20 cents or so more for premium. But as gas prices sneak back up, the mental wrangle begins anew over whether it's OK to burn cheaper, regular-grade gas.
AS PRICES RISE, CONSUMERS
SHUN PREMIUM GAS
Average price of a gallon of premium gasoline:
1993 $1.30
1999 $1.36
2002 $1.58
20031 $1.80
Premium gas share of all gas sold:
1993 19.9%
1999 16.8%
2002 13.5%
2003 12.1%
Sources: Energy Information Administration, American Petroleum Institute
The answer almost always is yes.
"I personally use regular even though my owner's manual says you'll get better performance with premium," says Lewis Gibbs, consulting engineer and 45-year veteran at Chevron oil company. He's chairman of Technical Committee 7 on Fuels, part of the Society of Automotive Engineers (SAE) Fuels & Lubricants Council. Gibbs knows gas.
"My wife runs midgrade (89 octane) in her car, and it's a turbocharged engine" meant for 91-octane premium, he says.
Premium — gasoline having an octane rating 91 or higher — is just 12.1% of sales this year, down from 13.5% in 2002, when it was 22 cents a gallon cheaper, and well below the modern high of 20.3% in 1994, when it was 49 cents cheaper, according to industry and government data. Despite the allure of premium, once they abandon it, most motorists don't come back, the data suggest.
For every dime increase in the price, sales of premium gas drop 1%, Bob Johnson, general manager of gasoline and environmental services for the 7-Eleven chain, figures, based on data back to 1998.
The main advantage of premium-grade gas is that it allows automakers to advertise a few more horsepower by designing and tuning engines to take advantage of premium's anti-knock properties. But auto engineers generally agree that if you use regular in a premium engine, the power loss is so slight, most drivers can't tell.
"I go back and forth, and I'm hard-pressed to notice" whether there's regular or premium in the tank, says Jeff Jetter, principal chemist at Honda Research and Development Americas. He drives an Acura designed for premium.
Import brands, especially, use premium fuel to distinguish their upmarket models. Most Toyotas, for instance, are designed to run on regular or midgrade, while the automaker's Lexus luxury brand prefers premium. Same with Honda and its Acura luxury line.
"Generally, the more expensive the vehicle, the higher the expectation for performance and the more the customer is willing to pay for fuel," says Pete Haidos, head of product planning for Nissan in the USA.
Actually, the price debate is nearly worthless. At 20 cents more for premium, pumping 20 gallons of it instead of regular would cost $4 more. Annually, that's a difference of $171 for a vehicle that averages 14 miles per gallon — as some big sport-utility vehicles do — and is driven 12,000 miles a year.
Gasoline retailers and refiners like high-test because it's more profitable than regular-grade gas is. The retailer paid about 8 cents more for the premium you pay 20 cents more for — though that margin can swing wildly. Refiners make a few cents a gallon more on premium than on regular when they sell to wholesale distributors.
As long as it's clean
Profit is meaningless to the modern engine, which, regardless of what's specified in the owner's manual, hardly cares what you use — as long as it's clean.
Today's engines use highly evolved versions of a device called a knock sensor to adjust settings automatically for low-octane gas. And more engine control computers have adequate memory to allow separate sets of instructions for various octanes. The engine control computers keep pushing to maximize performance on whatever grade of fuel is used.
Extreme pressure inside the cylinders causes knock, which is the sound of the pistons literally rattling inside the cylinders. Too much too long can damage the engine. A little now and then won't.
The only modern engines that should really need premium are those with superchargers, which force-feed fuel into the cylinders. "You're driving along and just tramp the gas and the knock sensor cannot sense the knock fast enough in some cases," because the supercharger boosts pressure so fast, says Bob Furey, chemist and fuels specialist at General Motors.
Burning regular when the owner's manual specifies premium won't void the warranty, nor damage the engine, even the most finicky automakers say. "You're giving up perhaps just a little bit of performance that a customer wouldn't really even notice, it's so slight," says Furey.
Automakers say they don't test premium engines on regular to check the difference, but some auto engineers estimate that power declines roughly 5%.
"We can't guarantee the vehicle will perform as specified if other than premium fuel is used," says Mercedes-Benz spokeswoman Michelle Murad. All U.S. Mercedes engines specify premium.
All Porsche engines are designed for premium, too, but it's not available everywhere. "Our cars must be able to drive all over the world, and so we are able to run on regular," says Jakob Neusser, director of powertrain development at Porsche's research and development center in Weissach, Germany. "You don't have to feel that a mechanical problem or anything else will happen" using regular gas, even in the highest-performance, regular-production Porsches.
Premium, in fact, sometimes is worse fuel than regular. It resists knock because it's harder to ignite than lower-octane fuels. As a result, some engines won't start as quickly or run as smoothly on premium, notes Gibbs, the SAE fuel expert.
High-test does have a potential fuel economy benefit. It is slightly denser than lower-octane gas, meaning there's a little more energy in a gallon. But the small difference is hard to measure in real-world use, and that same density can contribute to undesirable buildup of waste products inside the engine.
No data show that engines designed strictly for regular run better or longer on premium.
The Federal Trade Commission, in a consumer notice, emphasizes: "(I)n most cases, using a higher-octane gasoline than your owner's manual recommends offers absolutely no benefit. It won't make your car perform better, go faster, get better mileage or run cleaner."
There is "no way of taking advantage of premium in a regular-grade car," says Furey.
"There is no gain. You're wasting money," insists Jim Blenkarn, in charge of powertrains at Nissan in the USA.
"No customer should ever be deluded into thinking there's any value in buying a higher grade of octane than we specify," says Toyota's Paul Williamsen, technical expert and trainer.
But premium retains a mystique.
Even Mayne, the sensible Subaru owner who has switched to regular, says she'll buy premium when her neighborhood station has a special price. "It's my perception that I might get better gas mileage or that it might be better for my engine," she says.
"I would stop driving rather than use a lower grade of gasoline," says Andrew Martschenko of Boston, who drives a 2003 Nissan Maxima. Nissan says premium is "recommended" for that engine — automaker code for regular is OK, but you'll only get the advertised power on premium.
If the price difference between regular and premium grew to $1, Martschenko says, "Then I might consider trading down" to regular.
Guilt plays a part
Some people feel almost guilty, as if they are abusing their cars, when they don't burn premium, says gasoline retailer Jay Ricker, president of Ricker Oil of Anderson, Ind., which operates 28 stations. "They go all the way down to 87 (octane), but maybe every fourth tank they put in the good stuff."
Sam Turner has seen the appeal, too. He's president of Favorite Markets of Dalton, Ga., which operates 139 outlets in three states.
He recalls visiting one of his stations during a price war with a nearby station, which had cut the price of premium to just 4 cents more than regular, instead of the usual 20-cent difference.
"A customer was waiting and asked me if I was going to match the guy across the street. I said, 'Yeah,' and he said, 'Good. For 4 cents, I'm gonna buy super.' ".........."
So if it makes YOU feel good buy the expensive stuff but recognize it is doing NOTHING to make your low compression engine feel good......
Marti Mayne once fueled her low-octane Subaru with high-octane gas. Not now. Premium-gas prices "went sky high, and now I just use low grade" to motor around Yarmouth, Maine, where she runs a marketing business.
Cost differences between regular and premium is as plain as, well, the sign at the station, like this one in Chicago.
By Scott Olson, Getty Images
When prices dropped earlier this year, she stuck with cheaper fuel because "I don't think that my car runs any differently on high, medium or lower grade."
She's right. Engines designed for regular fuel don't improve on premium and sometimes run worse. And today's engines designed for premium run fine on regular, too, their makers say, though power declines slightly. (Background: About Octane ratings)
But premium lovers are passionate. "I would simply curtail driving rather than switch grades," says Bill Teater of Mount Vernon, Ohio, who puts high-test in both his Cadillacs, though only one recommends it. He's sure both the DeVille and the Escalade run rough and lack pep on regular.
Prejudice and preference aside, engineers, scientists and the federal government say there's little need for premium.
When fuel's cheap, motorists are willing to pay 20 cents or so more for premium. But as gas prices sneak back up, the mental wrangle begins anew over whether it's OK to burn cheaper, regular-grade gas.
AS PRICES RISE, CONSUMERS
SHUN PREMIUM GAS
Average price of a gallon of premium gasoline:
1993 $1.30
1999 $1.36
2002 $1.58
20031 $1.80
Premium gas share of all gas sold:
1993 19.9%
1999 16.8%
2002 13.5%
2003 12.1%
Sources: Energy Information Administration, American Petroleum Institute
The answer almost always is yes.
"I personally use regular even though my owner's manual says you'll get better performance with premium," says Lewis Gibbs, consulting engineer and 45-year veteran at Chevron oil company. He's chairman of Technical Committee 7 on Fuels, part of the Society of Automotive Engineers (SAE) Fuels & Lubricants Council. Gibbs knows gas.
"My wife runs midgrade (89 octane) in her car, and it's a turbocharged engine" meant for 91-octane premium, he says.
Premium — gasoline having an octane rating 91 or higher — is just 12.1% of sales this year, down from 13.5% in 2002, when it was 22 cents a gallon cheaper, and well below the modern high of 20.3% in 1994, when it was 49 cents cheaper, according to industry and government data. Despite the allure of premium, once they abandon it, most motorists don't come back, the data suggest.
For every dime increase in the price, sales of premium gas drop 1%, Bob Johnson, general manager of gasoline and environmental services for the 7-Eleven chain, figures, based on data back to 1998.
The main advantage of premium-grade gas is that it allows automakers to advertise a few more horsepower by designing and tuning engines to take advantage of premium's anti-knock properties. But auto engineers generally agree that if you use regular in a premium engine, the power loss is so slight, most drivers can't tell.
"I go back and forth, and I'm hard-pressed to notice" whether there's regular or premium in the tank, says Jeff Jetter, principal chemist at Honda Research and Development Americas. He drives an Acura designed for premium.
Import brands, especially, use premium fuel to distinguish their upmarket models. Most Toyotas, for instance, are designed to run on regular or midgrade, while the automaker's Lexus luxury brand prefers premium. Same with Honda and its Acura luxury line.
"Generally, the more expensive the vehicle, the higher the expectation for performance and the more the customer is willing to pay for fuel," says Pete Haidos, head of product planning for Nissan in the USA.
Actually, the price debate is nearly worthless. At 20 cents more for premium, pumping 20 gallons of it instead of regular would cost $4 more. Annually, that's a difference of $171 for a vehicle that averages 14 miles per gallon — as some big sport-utility vehicles do — and is driven 12,000 miles a year.
Gasoline retailers and refiners like high-test because it's more profitable than regular-grade gas is. The retailer paid about 8 cents more for the premium you pay 20 cents more for — though that margin can swing wildly. Refiners make a few cents a gallon more on premium than on regular when they sell to wholesale distributors.
As long as it's clean
Profit is meaningless to the modern engine, which, regardless of what's specified in the owner's manual, hardly cares what you use — as long as it's clean.
Today's engines use highly evolved versions of a device called a knock sensor to adjust settings automatically for low-octane gas. And more engine control computers have adequate memory to allow separate sets of instructions for various octanes. The engine control computers keep pushing to maximize performance on whatever grade of fuel is used.
Extreme pressure inside the cylinders causes knock, which is the sound of the pistons literally rattling inside the cylinders. Too much too long can damage the engine. A little now and then won't.
The only modern engines that should really need premium are those with superchargers, which force-feed fuel into the cylinders. "You're driving along and just tramp the gas and the knock sensor cannot sense the knock fast enough in some cases," because the supercharger boosts pressure so fast, says Bob Furey, chemist and fuels specialist at General Motors.
Burning regular when the owner's manual specifies premium won't void the warranty, nor damage the engine, even the most finicky automakers say. "You're giving up perhaps just a little bit of performance that a customer wouldn't really even notice, it's so slight," says Furey.
Automakers say they don't test premium engines on regular to check the difference, but some auto engineers estimate that power declines roughly 5%.
"We can't guarantee the vehicle will perform as specified if other than premium fuel is used," says Mercedes-Benz spokeswoman Michelle Murad. All U.S. Mercedes engines specify premium.
All Porsche engines are designed for premium, too, but it's not available everywhere. "Our cars must be able to drive all over the world, and so we are able to run on regular," says Jakob Neusser, director of powertrain development at Porsche's research and development center in Weissach, Germany. "You don't have to feel that a mechanical problem or anything else will happen" using regular gas, even in the highest-performance, regular-production Porsches.
Premium, in fact, sometimes is worse fuel than regular. It resists knock because it's harder to ignite than lower-octane fuels. As a result, some engines won't start as quickly or run as smoothly on premium, notes Gibbs, the SAE fuel expert.
High-test does have a potential fuel economy benefit. It is slightly denser than lower-octane gas, meaning there's a little more energy in a gallon. But the small difference is hard to measure in real-world use, and that same density can contribute to undesirable buildup of waste products inside the engine.
No data show that engines designed strictly for regular run better or longer on premium.
The Federal Trade Commission, in a consumer notice, emphasizes: "(I)n most cases, using a higher-octane gasoline than your owner's manual recommends offers absolutely no benefit. It won't make your car perform better, go faster, get better mileage or run cleaner."
There is "no way of taking advantage of premium in a regular-grade car," says Furey.
"There is no gain. You're wasting money," insists Jim Blenkarn, in charge of powertrains at Nissan in the USA.
"No customer should ever be deluded into thinking there's any value in buying a higher grade of octane than we specify," says Toyota's Paul Williamsen, technical expert and trainer.
But premium retains a mystique.
Even Mayne, the sensible Subaru owner who has switched to regular, says she'll buy premium when her neighborhood station has a special price. "It's my perception that I might get better gas mileage or that it might be better for my engine," she says.
"I would stop driving rather than use a lower grade of gasoline," says Andrew Martschenko of Boston, who drives a 2003 Nissan Maxima. Nissan says premium is "recommended" for that engine — automaker code for regular is OK, but you'll only get the advertised power on premium.
If the price difference between regular and premium grew to $1, Martschenko says, "Then I might consider trading down" to regular.
Guilt plays a part
Some people feel almost guilty, as if they are abusing their cars, when they don't burn premium, says gasoline retailer Jay Ricker, president of Ricker Oil of Anderson, Ind., which operates 28 stations. "They go all the way down to 87 (octane), but maybe every fourth tank they put in the good stuff."
Sam Turner has seen the appeal, too. He's president of Favorite Markets of Dalton, Ga., which operates 139 outlets in three states.
He recalls visiting one of his stations during a price war with a nearby station, which had cut the price of premium to just 4 cents more than regular, instead of the usual 20-cent difference.
"A customer was waiting and asked me if I was going to match the guy across the street. I said, 'Yeah,' and he said, 'Good. For 4 cents, I'm gonna buy super.' ".........."
So if it makes YOU feel good buy the expensive stuff but recognize it is doing NOTHING to make your low compression engine feel good......
06-13-2011, 03:51 PM
#37
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Come on Jim, do you really believe all those engineers, with their fancy degrees and reasearch? Everybody should be buying premium!! There's a very good reason for everybody to do that. I own oil company stock.
06-13-2011, 04:06 PM
#38
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Jim:
Yes, I'm aware of the 90 octane (US rating) recommendation in the owners manual. I don't recall why I started using 87 octane, but I observed that there were no knocks on 87 octane w/o the supercharger. With the supercharger, I would get occasional audible knocks even on 91 octane, even though the boost was modest, especially on a hot day with higher engine coolant and air intake temps. Anyway, I'm very happy with the performance on 87 octane in my 89 S4 that has an x-pipe but is otherwise stock, so I'm not too motivated to try 91 and perhaps advance timing to see if it does any better. I haven't dyno'd it in this configuration but I may soon and perhaps could do the experiment you suggest. Anyway, my experience is that S4s do fine on lower octane with excellent performance while GT and GTS models need higher octane, and I've seen a lot of GTS models that still knock on 91 (usually later shown to be due to coking of the combustion chamber).
I remember stating this in a group of local 928 owners who all got flabbergasted looks on their faces and literally told me I was wrong. Oh, well. I don't mind being different and my car doesn't either.
Yes, I'm aware of the 90 octane (US rating) recommendation in the owners manual. I don't recall why I started using 87 octane, but I observed that there were no knocks on 87 octane w/o the supercharger. With the supercharger, I would get occasional audible knocks even on 91 octane, even though the boost was modest, especially on a hot day with higher engine coolant and air intake temps. Anyway, I'm very happy with the performance on 87 octane in my 89 S4 that has an x-pipe but is otherwise stock, so I'm not too motivated to try 91 and perhaps advance timing to see if it does any better. I haven't dyno'd it in this configuration but I may soon and perhaps could do the experiment you suggest. Anyway, my experience is that S4s do fine on lower octane with excellent performance while GT and GTS models need higher octane, and I've seen a lot of GTS models that still knock on 91 (usually later shown to be due to coking of the combustion chamber).
I remember stating this in a group of local 928 owners who all got flabbergasted looks on their faces and literally told me I was wrong. Oh, well. I don't mind being different and my car doesn't either.
This is interesting, Bill. According to the US '89 owners manual copy that I have, the requirement is for 95 RON or 90 US octane (R+M)/2. Is that what your manual says also?
So if Sharktuner is not picking up any knock-retards with 87 octane then there is enough margin with compression and ignition timing, to avoid any detonation.
The question then is this: If you used higher-octane (slower-burning) fuel and didn't change ignition timing, would you get less horsepower? (Or lower efficiency at highway speeds, i.e. lower mileage?).
My thinking here is that, for a given engine RPM and load, ignition timing is ideally adjusted to maximize the efficiency of the engine-- max HP at that operating point. Because combustion takes some time (depending on temperature, pressure and octane), the spark starts the combustion early, before the piston is at TDC. If the fuel burns too fast, and the pressure/temperature gets above a critical point while the piston is still traveling upwards (and compressing the mixture) and detonation results.
And there will also be less power, because the piston is pushing against the increasing pressure, rather than being pushed by it. The fix here is to reduce the ignition advance, and light the fire later because it is going to burn faster.
And conversely, if the fuel burns more slowly (i.e. higher octane), then the maximum pressure will occur later, and some of the power will be lost because the piston is beyond the optimum point as the combustion pressure increases.
If this is correct, then I would think that running a higher-than-needed octane would actually result in less HP, unless the ignition advance were also adjusted.
So here is what has me really scratching my head: If you take an engine which is happy on 87 octane (i.e. no detectable detonation), and switch to 91 octane and also advance the timing by whatever is appropriate (a few degrees?), does that result in a net increase in power? Or is the result the same as 87 octane and original timing?
Cheers,
So if Sharktuner is not picking up any knock-retards with 87 octane then there is enough margin with compression and ignition timing, to avoid any detonation.
The question then is this: If you used higher-octane (slower-burning) fuel and didn't change ignition timing, would you get less horsepower? (Or lower efficiency at highway speeds, i.e. lower mileage?).
My thinking here is that, for a given engine RPM and load, ignition timing is ideally adjusted to maximize the efficiency of the engine-- max HP at that operating point. Because combustion takes some time (depending on temperature, pressure and octane), the spark starts the combustion early, before the piston is at TDC. If the fuel burns too fast, and the pressure/temperature gets above a critical point while the piston is still traveling upwards (and compressing the mixture) and detonation results.
And there will also be less power, because the piston is pushing against the increasing pressure, rather than being pushed by it. The fix here is to reduce the ignition advance, and light the fire later because it is going to burn faster.
And conversely, if the fuel burns more slowly (i.e. higher octane), then the maximum pressure will occur later, and some of the power will be lost because the piston is beyond the optimum point as the combustion pressure increases.
If this is correct, then I would think that running a higher-than-needed octane would actually result in less HP, unless the ignition advance were also adjusted.
So here is what has me really scratching my head: If you take an engine which is happy on 87 octane (i.e. no detectable detonation), and switch to 91 octane and also advance the timing by whatever is appropriate (a few degrees?), does that result in a net increase in power? Or is the result the same as 87 octane and original timing?
Cheers,
06-13-2011, 05:17 PM
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You can probably get away with running lower grade fuels in vehicles equipped with knock sensors - but even then you won't profit as much as you'd think, because the car would actually use more of that lower-grade fuel.
On the other hand, you absolutely do not want to run lower grade than specified in those higher compression engines w/o any knock control (for example, CIS euros, etc).
I personally think that the best idea is to run what manufacturer suggests and neither go higher octane, nor lower.
EDIT: Oh, and:
Ye, it's the same for us here, - we also have 92 too actually. But, its not the same octane rating as in US. Eu one is RON, while US is (RON+MON)/2 Our 95 is ~US 91 and Eu98 is ~US93. Hope that made sense.
On the other hand, you absolutely do not want to run lower grade than specified in those higher compression engines w/o any knock control (for example, CIS euros, etc).
I personally think that the best idea is to run what manufacturer suggests and neither go higher octane, nor lower.
EDIT: Oh, and:
Ye, it's the same for us here, - we also have 92 too actually. But, its not the same octane rating as in US. Eu one is RON, while US is (RON+MON)/2 Our 95 is ~US 91 and Eu98 is ~US93. Hope that made sense.
06-13-2011, 08:22 PM
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I ran regular gas on the auto for years. Only once in a bit of heat-wave we had, did the engine ever act disturbed.
There was a slight detonation upon full throttle.
Otherwise any performance gains were moot.
I was surprised.
There was a slight detonation upon full throttle.
Otherwise any performance gains were moot.
I was surprised.
06-13-2011, 10:46 PM
#41
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From the Porsche spec books:
1978 - 1979 M28.01/02/03/04 8.5:1 compression Fuel: 91 RON Regular
1980 - 1984: US 9.0:1 compression USA 91 RON Leadfree (vs. 98 RON for Euro)
The 1980 - 1984 L-Jetronic fuel injection provides a more precise air/fuel ratio and lambda regulation, that is likely how they got by with a slightly higher compression ratio with regular fuel.
As explained, the US uses (RON + MON)/2, so the number is lower. With the low compression of the US motors up to 1984, there is no need for premium fuel and Porsche did not specify using it.
1978 - 1979 M28.01/02/03/04 8.5:1 compression Fuel: 91 RON Regular
1980 - 1984: US 9.0:1 compression USA 91 RON Leadfree (vs. 98 RON for Euro)
The 1980 - 1984 L-Jetronic fuel injection provides a more precise air/fuel ratio and lambda regulation, that is likely how they got by with a slightly higher compression ratio with regular fuel.
As explained, the US uses (RON + MON)/2, so the number is lower. With the low compression of the US motors up to 1984, there is no need for premium fuel and Porsche did not specify using it.
06-13-2011, 11:05 PM
#42
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The only monkey wrench in all of this is ethanol content, assuming it continues to rise in "regular" fuel. Around here, most stations are "ethanol free" for high test, and up to 10% in the other two.
That 10% is set to rise, I hope the premium fuel still stays e-free.
I have nothing against the use of ethanol, in cars designed for it. I don't like it forced upon me.
That 10% is set to rise, I hope the premium fuel still stays e-free.
I have nothing against the use of ethanol, in cars designed for it. I don't like it forced upon me.
06-14-2011, 01:12 AM
#43
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fuel aditives
i always use 91 oct in my 82 and use an fuel adative i always thought it would make the engine burn cleaner.
Last edited by camc61; 06-14-2011 at 01:41 AM. Reason: miss information
06-14-2011, 06:56 PM
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Interesting to compare output and compression ratios...."I doubt that Porsche received any complaints about the power and response of the 996 GT3’s 375bhp flat-six, but for the new GT3 the naturally aspirated 3.6-litre engine has been subjected to a meticulous, obsessive drive to reduce internal masses. The short-stroke, dry-sumped boxer six now revs to a maximum of 8400rpm, 200rpm higher, and with the help of a mild ram-air effect from the engine-cover air scoops, a larger intake butterfly and a compression ratio up from 11.7 to 12.0 to one, it develops a heady 409bhp at 7600rpm. That gives it an exceptional rating of 114bhp per litre and makes it almost as powerful as the twin-turbo 3.6 fitted to the 996 Turbo....."
12 to 1 compression !!!!! 114 HP per liter, now THAT is high performance. I think it NEEDS premium
12 to 1 compression !!!!! 114 HP per liter, now THAT is high performance. I think it NEEDS premium