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Old 08-20-2007, 11:18 PM   #1
whicky1978
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compression ratio vs. octane rating

If I have a 10.3:1 compression ratio, then what is the maximum octane fuel my car could handle? Does anybody know of a website with a chart?
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Old 08-20-2007, 11:24 PM   #2
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Quote:
Originally Posted by whicky1978
If I have a 10.3:1 compression ratio, then what is the maximum octane fuel my car could handle? Does anybody know of a website with a chart?
That highly depends on the motor...
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Old 08-20-2007, 11:29 PM   #3
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Originally Posted by 67Coronet383
That highly depends on the motor...

What if it's a DOHC engine?
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Old 08-21-2007, 12:33 AM   #4
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I think you mean minimum. That depends on alot more than just static compression. What motor? It could be anywhere from 87 to 93. Is the head alluminum?
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Old 08-21-2007, 02:15 AM   #5
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I know the minimum is 87 AKI (R+M/2 method). Is it possible to have too much octane in gasoline for a car? I drive a 2005 Hyundai Elantra GSL.

Edit: I drive a 2001. My wife drives a 2005 PT cruiser, premium gas only gave her car 2 more miles per gallon.

Last edited by whicky1978 : 08-22-2007 at 02:40 AM.
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Old 08-21-2007, 04:00 AM   #6
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Quote:
Originally Posted by whicky1978
Is it possible to have too much octane in gasoline for a car?

Yes sir. If you adjust timing to a certain extent you can harness the benefits of higher octane fuel, but pretty much only if you adjust for it. If you put 91 in a car meant to run 87 you won't be doing too much harm, maybe clogging some cats, foulding the chambers, and losing power, but ti wouldn't be catastrophic. Alot of engines are quite high strung though, especially modern ones. If you put 87 in a 91 modern car typically it will pull the timing which reduces power. If it doesn't have a knock sensor though, or if it is broken, then it won't notice and you will have detonation. Depending on severity of the detonation you can junk the motor, and you will be running alot less power.

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Old 08-22-2007, 12:41 AM   #7
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That sounds goood. I mostly use premium because of the extra fuel economy it gives me. I average 34-37 mpg. I'm do for a new timing belt, if they adjust the belt for higher octane, will I see better fuel economy or more power or both, or would it be the same because the car adjust according to the knock sensor?
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Old 08-22-2007, 01:45 AM   #8
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Quote:
Originally Posted by whicky1978
That sounds goood. I mostly use premium because of the extra fuel economy it gives me. I average 34-37 mpg. I'm do for a new timing belt, if they adjust the belt for higher octane, will I see better fuel economy or more power or both, or would it be the same because the car adjust according to the knock sensor?
What the f*ck is wrong with you you simple minded moron? We have already played this silly ass game with you. No matter what you think, running gasoline with a higher octane rating than your car requires WILL NOT INCREASE FUEL ECONOMY! Your Hyundai is optimized to run on 87 octane. Using higher octane gas is at best a waste of money and at worst can actually cause you to lower your fuel mileage and cause damage to your catalytic convertor.

I don't care what you think. This has been tested over and over ad infinitum by manufacturers, oil companies, private research firms, car magazines, etc. Unless you want us to believe the you are the one and only person on the face of the earth that sees decreased consumption when increasing octane in an engine that isn't designed for it, then just STFU... Moron.
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Old 08-22-2007, 01:50 AM   #9
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Originally Posted by vwhobo
What the f*ck is wrong with you you simple minded moron? We have already played this silly ass game with you. No matter what you think, running gasoline with a higher octane rating than your car requires WILL NOT INCREASE FUEL ECONOMY! Your Hyundai is optimized to run on 87 octane. Using higher octane gas is at best a waste of money and at worst can actually cause you to lower your fuel mileage and cause damage to your catalytic convertor.

I don't care what you think. This has been tested over and over ad infinitum by manufacturers, oil companies, private research firms, car magazines, etc. Unless you want us to believe the you are the one and only person on the face of the earth that sees decreased consumption when increasing octane in an engine that isn't designed for it, then just STFU... Moron.
What about higher octane being used to clean the fuel system, valves, injectors, etc.etc. from time-to-time.
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Old 08-22-2007, 02:17 AM   #10
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Originally Posted by newyorker
What about higher octane being used to clean the fuel system, valves, injectors, etc.etc. from time-to-time.
Octane DOES NOT clean anything. Octane in layman’s terms is a measure of resistance to detonation. Too high of an octane may actually burn too cool and create/increase carbon deposits in the combustion chamber, exhaust ports (including valves), exhaust and damage the cat.

Additive packages added to gasoline at the refinery, specifically detergents, can clean or keep clean fuel system and engine mechanical components. All gasoline sold in the USA has a minimum required amount of detergent by law. For most cars under most circumstances this is plenty of "cleaning". If you're concerned, run a bottle of Lucas fuel treatment through the engine (follow the directions) every oil change.

The biggest problem with gas in the US is not what comes from the refineries. It's the cleanliness of the tanker it's transported in and most importantly the underground tanks it's stored in at the gas station. Avoid the high dollar stations that move gas slowly. Purchase at the places that move it the fastest, which are usually the cheapest places in town. In many cases the gas is exactly the same gas from exactly the same truck, just different names and prices on the pump.

Also keep your tank as full as is reasonably possible at all times. The lower the the fuel level, the more space there is for condensation to form in the tank. Up north where you live, the cold of winter and the humid summers will fill (not literally) a gas tank with water. Same thing in the deep south where I live. Humidity, humidity, humidity. Even in the arid southwest, condensation will accumulate in an empty(ish) tank. Eight ounces of denatured alcohol every three months will take care of it for the most part and help keep your tank clean.


True story. A week or so ago the fuel pump on my '95 Dakota finally crapped out. Twelve years old and 240k+ miles on the original pump and tank, never been dropped, and when I drained it I let the gas and water seperate, just to see. Guess what? It had absolutely zero water and essentially no sediment. It's amazing what being cheap enough to do just a little preventative maintenance will do.


Edit: I knew after typing that much I'd forget something. Try not to fill your tank at a station within about 12 hours of their tanks being filled. As you can imagine having a tanker dump it's load causes some turbulence in the underground tank. This serves to stir up all the sh*t down there and if you fill up too soon, some of will get into your tank. The 12 hour cool off period gives it a chance to settle.
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Last edited by vwhobo : 08-22-2007 at 02:30 AM.
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Old 08-22-2007, 06:36 AM   #11
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Quote:
Originally Posted by vwhobo
Octane DOES NOT clean anything. Octane in laymanís terms is a measure of resistance to detonation. Too high of an octane may actually burn too cool and create/increase carbon deposits in the combustion chamber, exhaust ports (including valves), exhaust and damage the cat.

Additive packages added to gasoline at the refinery, specifically detergents, can clean or keep clean fuel system and engine mechanical components. All gasoline sold in the USA has a minimum required amount of detergent by law. For most cars under most circumstances this is plenty of "cleaning". If you're concerned, run a bottle of Lucas fuel treatment through the engine (follow the directions) every oil change.

The biggest problem with gas in the US is not what comes from the refineries. It's the cleanliness of the tanker it's transported in and most importantly the underground tanks it's stored in at the gas station. Avoid the high dollar stations that move gas slowly. Purchase at the places that move it the fastest, which are usually the cheapest places in town. In many cases the gas is exactly the same gas from exactly the same truck, just different names and prices on the pump.

Also keep your tank as full as is reasonably possible at all times. The lower the the fuel level, the more space there is for condensation to form in the tank. Up north where you live, the cold of winter and the humid summers will fill (not literally) a gas tank with water. Same thing in the deep south where I live. Humidity, humidity, humidity. Even in the arid southwest, condensation will accumulate in an empty(ish) tank. Eight ounces of denatured alcohol every three months will take care of it for the most part and help keep your tank clean.


True story. A week or so ago the fuel pump on my '95 Dakota finally crapped out. Twelve years old and 240k+ miles on the original pump and tank, never been dropped, and when I drained it I let the gas and water seperate, just to see. Guess what? It had absolutely zero water and essentially no sediment. It's amazing what being cheap enough to do just a little preventative maintenance will do.


Edit: I knew after typing that much I'd forget something. Try not to fill your tank at a station within about 12 hours of their tanks being filled. As you can imagine having a tanker dump it's load causes some turbulence in the underground tank. This serves to stir up all the sh*t down there and if you fill up too soon, some of will get into your tank. The 12 hour cool off period gives it a chance to settle.
Thanks for the clarification. I also heard that if you run the tank too low, and there are any contaminants in the tank, they can "clog" the pump...not sure if this is true either.

As far as what you said with octane, there are certain fuel system cleaners out there with octane booster...wouldnt these be giving the same effect as higher octane gas, but at a more expeditious rate?? I usually try to keep my tank at above 1/2 level, but lately ive been neglecting it a bit.
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Old 08-22-2007, 02:07 PM   #12
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Quote:
Originally Posted by newyorker
Thanks for the clarification. I also heard that if you run the tank too low, and there are any contaminants in the tank, they can "clog" the pump...not sure if this is true either.

As far as what you said with octane, there are certain fuel system cleaners out there with octane booster...wouldnt these be giving the same effect as higher octane gas, but at a more expeditious rate?? I usually try to keep my tank at above 1/2 level, but lately ive been neglecting it a bit.
I've heard the same thing for years myself. Whenever I do, I ask the person making the statement this;

"Any contaminant that may be in your gas tank, be it water, rust, dirt or some other type of sediment, is heavier than the gasoline. That means it'll always be at the bottom of the tank... The same place the fuel pick-up is located. Based on these facts, specifically that the junk will always be on the bottom and the pick-up is at the bottom, how will running low on gas cause you to pick-up any more junk?"

I'm always given a "deer in the headlights" look followed by them stammering something about that's what their father/mother/brother/sister/next door neighbor/mechanic/bag boy at the grocery store/palm reader/homosexual lover/second grade teacher/etc told them, so it must be true. Well it's not.

That being said, a car that has an electric fuel pump will see increased wear and shorter service life of the fuel pump if you make it a habit of running the tank way low on fuel. The only thing that cools and lubricates that little motor that spins about a bazillion RPM and keeps it alive is the fuel being pumped through it and in the case of an in-tank pump, the fuel it's submerged in.



Fuel system cleaner with octane booster. I can't recommend them. Most every engine I've been in, whether just replacing plugs or a full rebuild that has been run with any form of octane booster has a fair amount of deposits left behind because of the booster. That being said, most people who run octane booster probably do so to excess and that's probably part of the cause. On the other hand, if you follow the directions, you'll only use it once a month, so what's the point? My call? Stay away and invest your money in mutual funds.
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Old 08-22-2007, 05:12 PM   #13
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Quote:
Originally Posted by vwhobo
I've heard the same thing for years myself. Whenever I do, I ask the person making the statement this;

"Any contaminant that may be in your gas tank, be it water, rust, dirt or some other type of sediment, is heavier than the gasoline. That means it'll always be at the bottom of the tank... The same place the fuel pick-up is located. Based on these facts, specifically that the junk will always be on the bottom and the pick-up is at the bottom, how will running low on gas cause you to pick-up any more junk?"

I'm always given a "deer in the headlights" look followed by them stammering something about that's what their father/mother/brother/sister/next door neighbor/mechanic/bag boy at the grocery store/palm reader/homosexual lover/second grade teacher/etc told them, so it must be true. Well it's not.

That being said, a car that has an electric fuel pump will see increased wear and shorter service life of the fuel pump if you make it a habit of running the tank way low on fuel. The only thing that cools and lubricates that little motor that spins about a bazillion RPM and keeps it alive is the fuel being pumped through it and in the case of an in-tank pump, the fuel it's submerged in.



Fuel system cleaner with octane booster. I can't recommend them. Most every engine I've been in, whether just replacing plugs or a full rebuild that has been run with any form of octane booster has a fair amount of deposits left behind because of the booster. That being said, most people who run octane booster probably do so to excess and that's probably part of the cause. On the other hand, if you follow the directions, you'll only use it once a month, so what's the point? My call? Stay away and invest your money in mutual funds.
While that qoute sounds true, I dont get one thing. You say it will be on the bottom of the tank, but routine driving does see some bumps, and that causes the gasoline to splash around right? Wouldnt that cause all of the crap at the bottom to be constantly floating around? Or are gas tanks not just tanks, but have some kind of dividers in them like oil pans?

Last question. Is it true that higher viscosity motor oil is better for higher milage motors. I use 5w-20, but at 115k some have told me to go to 5w-30 to be a bit kinder to the engine. I already use synthetic, but would the swich be of any benefit??

EDIT: also, does a magnetic oil drain plug hold any real benefit compared to a non-magnetic??
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Last edited by newyorker : 08-22-2007 at 05:17 PM.
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Old 08-22-2007, 06:32 PM   #14
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You won't get better economy with premium in a regular engine. The only way you would would be if the O2 sensors were compensating and leaning out the mixture. In this case you probably wouldn't mess up the cats and yes you would get better economy... but you would lose horsepower. Horsepower and economy oppose eachother. I doubt this is happening though.
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Old 08-22-2007, 08:32 PM   #15
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Quote:
Originally Posted by newyorker
While that qoute sounds true, I dont get one thing. You say it will be on the bottom of the tank, but routine driving does see some bumps, and that causes the gasoline to splash around right? Wouldnt that cause all of the crap at the bottom to be constantly floating around? Or are gas tanks not just tanks, but have some kind of dividers in them like oil pans?

Last question. Is it true that higher viscosity motor oil is better for higher milage motors. I use 5w-20, but at 115k some have told me to go to 5w-30 to be a bit kinder to the engine. I already use synthetic, but would the swich be of any benefit??

EDIT: also, does a magnetic oil drain plug hold any real benefit compared to a non-magnetic??
1. Yes, there is no doubt in my mind that driving may indeed cause some of the swill at the bottom of your tank to move around. But unless you're driving the Baja 1000 I believe it would be minimal. Also keep in mind that no matter what, gravity is still eventually going to take it back to the lowest part of the tank, which also just happens to be where the pick-up is. How much crap has settled there after sitting overnight waiting for the first start of the morning?

2. Many modern fuel tanks have a sump area, much like your oil pan example, to prevent fuel from sloshing away from the pick-up during acceleration, deceleration and cornering. Depending on the design they can also help, but not entirely prevent the pump from picking up debris.

3. The reason modern engine use lower viscosity oils are two-fold. One, is for lower lubricating system operating losses especially when the engine is cold. This can help achieved the all important higher EPA fuel mileage ratings. Two, because modern engines have much tighter operating tolerances than engines of old, it allows the pressurized oil to reach all parts of the engine sooner after start-up, especially when cold. Notice a trend? I personally recommend using somewhat higher viscosity oil as the engine wears, 100k being my transition point, and also in places that see extended periods of hot weather (it's 102F here right now). Knowing what little I do about your car, I would recommend 10W-40 in the summer and 5W-30 in the winter.

4. I think a magnetic drain plug is one of those things that may not be real helpful, but they sure can't hurt. Plus they're cheap and cause no extra work to install. I don't have magnetic plugs in any of my stuff unless they came that way from the factory. I do however recommend them to all my customers that need a drain plug replaced because... Well because I make a little more money on them.



Quote:
Originally Posted by rudypoochris
You won't get better economy with premium in a regular engine. The only way you would would be if the O2 sensors were compensating and leaning out the mixture. In this case you probably wouldn't mess up the cats and yes you would get better economy... but you would lose horsepower. Horsepower and economy oppose eachother. I doubt this is happening though.
Really? Are you sure? Horsepower and economy oppose each other? If I have two engines of the same design and displacement, engine A with a VE of 90% that produces 100 hp and engine B with a VE of 50% that produces 90 hp, which one uses less fuel at maximum power? If you answered engine A you're correct, but it makes less power, so... Care to explain the discrepancy?

Think, type, submit.
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