Quoted: Quoted: When I purchased my Land Rover in 1999 it was placarded with warnings to run only 92 octane or greater fuel.  I did this to protect my investement.  Some months later I was reading an australian Land Rover site which said 87 octane or greater.  I asked the service manager at the dealership why the difference?  He said because Americans buying premium cars expect them to run on premium fuel.  He further stated that 87 octane would not hurt the car and I would notice little or no difference. What was the compression ratio on the engine?

My 95 LR Discovery 3.9l
9.35:1
I always put + in mine. If I go with the lower octane the engine knocks like a mofo. And gas milage really sux! In the owner manual it states use premium of a 90 or 92 AKI octane. And goes on to explain the knocking assoc with lower octane fuel.

Quoted: Quoted: As long as the car isn't pinging, nothing is being damage. Your car isn't pinging because the computer RETARDED the timing! You don't use a timing light anymore, the timing gets set automatically by the computer. Like everyone says...it's all about compression ratio.  Nothing else.  Low ocatane in high compression engines WILL affect perfromance and power. ANd why would you send big bucks on a car just  to save .20 cents a gallon is gas anyways?  That's like shooting Wolf ammo  out of a match AR15 rifle at Camp Perry! SGtar15 SGatr15

Because if your car runs fine off of lower octane, then you're not gaining ANYTHING by using higher octane.  

If your engine is a low compression engine, and the manufacturer recommends high octane, it's either they want to make you feel like your car is special, or more high end, they're helping out their buddies in the oil/gas industry, or they have a computer that will fuck up your timing if you use lower octane.   It's possible to have a lower compression engine with a computer tuned to use higher octane that could react poorly to lower octane.   Most will just use an advanced timing with higher octane, and will back it down with lower octane, but will not suffer damage from lower octane.  

If my car runs fine off of 87, regardless of the recommendations, why should I spend more filling it up every week?  

Quoted: Quoted: I'm going to put 87 octane in my Lightning now, becuase this article says that will get me better mileage! Actually, I'd save a hell of a lot of gas money if I blew it up So you spent $30+ k on a high performance truck that gets extreme(for a truck) horsepower.   It has all the cool gismos and doodads that make it look and go fast. Yet you are going to use CHEAPER gas to save fuel economy?? WTF????? ANd this is all based one 1 article? SGtar15

He was being facetious srgt15

Quoted: Quoted: Some cars engines will rattle, ping, and knock like hell if they aren't fed premium go juice. It's your car so I don't much care what you put in it. That is because some cars are designed to compress the fuel more than others, if a car that is designed for higher octane gas is ran with lower, what will happen is that the fuel will reach a high enough compresion to detonate before the timing of the engine is ready for it, meaning that the valves are not in ideal position and the spark plug is not firing at the optimum time. Running higer octane fuel in a lower compression engine will not make a difference, the spark plug will simply ignite the fuel mixture at the appopriate time.

Not quite.

The fuel air mixture in your cylinder is never supposed to detonate.  It is supposed to burn.  Detonation is like using too fast a powder in your reloads, the same amount of energy is released, but it is released too fast, causing damage.

My 4 cylinder twin turbo Saab recommends use of high octane gas but says regular gas may be used instead, but you may experience a loss of performance in warmer months

I use high octane as a result.  Thankfully I get over 32 mpg highway with the thing

Quoted: Not quite. The fuel air mixture in your cylinder is never supposed to detonate.  It is supposed to burn.  Detonation is like using too fast a powder in your reloads, the same amount of energy is released, but it is released too fast, causing damage.

Not quite.

Detonation with a fuel air mixture is when the mix spontaneously ignites due to the temperature increase of being compressed.   It is NOT like using a powder that is too fast.    Detonation is when the fuel air mix ignites before the spark plug fires.  This usually happens before the piston finishes the compression stroke, and can cause failure of related parts (piston, rod, crank...)

Most any hyrocarbon, when compressed, at some point, will detonate.  Octane is very resistant to it, where heptane is very prone to detonate.  The octane rating in gasoline is the relative ratio of octane to heptane.  

Most of what is being said is correct.  HOWEVER, I will always urge people to follow the manufacturers instructions.  Even in a low-compression engine, it is possible to tune the engine for a higher-octane fuel.  This results in more power and efficiency when using this fuel, and less when using virtually anything else.  (There are also 'chips' that do this to cars that don't have it done at the factory, sometimes with dramatic performance gains).

So saying that you can ALWAYS use 87 in a low compression engine is INCORRECT.  USUALLY you can.  But if your manual says not to, there just might be a reason.  

But in an engine that normally runs fine on 87, just stick with that.

Quoted: If my car runs fine off of 87, regardless of the recommendations, why should I spend more filling it up every week?

ARe you listening?


No care with lower compression engines ever recommends higher octane gas.  Even more Ford SUV recommends 87.  Being able to produce a motor that uses the cheaper 87 octane is a SELLING point for car makers, the car makers goal is to REDUSE costs...so why would they recommend higher octane?  Especially when they KNOW, like you stated, that it wopuld do nothing?


All everyone is saying is that high octane gas is only for higher compression engines.


It really is that simple.

If you have a low compression engine and use high ocatne you waste money.

If you have a higher compression engine and you use 87 octane then you are not getting the most out of that engine.


Simple...really, it is.


Sgtar15

Quoted: Most of what is being said is correct.  HOWEVER, I will always urge people to follow the manufacturers instructions.  ....... But if your manual says not to, there just might be a reason.  .

That's what I am saying.  I am pretty sure the guys that built my truck knew more about cars then I ever will.


SGtar15


PS  and that whole warrenty thingy......

I'm telling you guys that it comes down to auto manufacuter's not wanting to get sued for false advertising.

If they say that an engine gets 300hp then they'd better be able to prove it or else face massive law suites.

Using higher octane gasoline CAN produce more power IF then engine is designed for it by having the proper valve timing and compression ratio.

If you've got a little econobox where nobody cares if it can't pass a fat boy on a bicycle, then horsepower is not an issue.  On the other hand, if you just bought the latest Japanese or German touring car, horsepower is a key selling point and manufacturers will do whatever they can to get the highest publishable rating, including using high octane fuel so that the timing does NOT automatically retard and a few extra horsepower are gained.

A lot of the misunderstanding here probably comes from historical data that was correct....at one time.

Any modern auto engine has knock sensors and will retard the timing as necessary to prevent pinging. If your car is not pinging, BUT is running with it's maximum timing advance, then using higher octane fuel is just a waste of cash.

Ed

Quoted: Quoted: As long as the car isn't pinging, nothing is being damage. Your car isn't pinging because the computer RETARDED the timing! You don't use a timing light anymore, the timing gets set automatically by the computer. Like everyone says...it's all about compression ratio.  Nothing else.  Low ocatane in high compression engines WILL affect perfromance and power. ANd why would you send big bucks on a car just  to save .20 cents a gallon is gas anyways?  That's like shooting Wolf ammo  out of a match AR15 rifle at Camp Perry! SGtar15 SGatr15

Sgtar is right, if the computer senses detonation, it will retard the timing to help minimize the knock. When your computer retards the timing you are also costing yourself horsepower and fuel efficency. So the simple way to think of it is, higher octane fuel by itself doesn't add power, but using higher octane fuel allows a vehicle to maximize it's power it was designed for. (again, this doesn't apply to most cars on the road, only higher compression engines running more timing advance)

Quoted: I'm telling you guys that it comes down to auto manufacuter's not wanting to get sued for false advertising. If they say that an engine gets 300hp then they'd better be able to prove it or else face massive law suites. Using higher octane gasoline CAN produce more power IF then engine is designed for it by having the proper valve timing and compression ratio. If you've got a little econobox where nobody cares if it can't pass a fat boy on a bicycle, then horsepower is not an issue.  On the other hand, if you just bought the latest Japanese or German touring car, horsepower is a key selling point and manufacturers will do whatever they can to get the highest publishable rating, including using high octane fuel so that the timing does NOT automatically retard and a few extra horsepower are gained. A lot of the misunderstanding here probably comes from historical data that was correct....at one time. Any modern auto engine has knock sensors and will retard the timing as necessary to prevent pinging. If your car is not pinging, BUT is running with it's maximum timing advance, then using higher octane fuel is just a waste of cash. Ed

You beat me to it, but explained it better than me anyway.


+1000

Quoted: Quoted: My car requires premium gas.  The computer controls the entire vehicle (including the throttle ), so if lower octane gas is used it will not hurt the engine.  I WILL however see a decrease in my fuel economy.  On one of the car message boards I frequent, they did a survey and determined the loss in fuel economy from using regular made the overall cost of fuel almost exactly the same whether you used permium or regular.   I severely doubt that.  With higher octane in a non-high compression engine, the computer is compensating for the HIGHER octane... when it really doesn't need to.  Higher octane gas DOES NOT PROVIDE MORE POWER.  It does not burn more cleanly, and infact doesn't burn as well unless at higher temperatures, which you usually won't see in a daily driver.   Switching to lower octane and getting a loss in fuel economy is probably because of the driver.   The forum you mention probably can't be taken as scientific evidence of lower fuel economy.  If you and I drive the exact same vehicle, but use different grades of fuel, we simply can't compare our fuel economy as evidence of difference in octane grades.  Our driving habits may be VERY different, and there are many factors that will affect the outcome.   High octane in anything other than high compression engines is a waste.

My car does have a high compression engine and thus the requirment of premium fuel, the computer can adjust for the lower octane gas to avoid the detonation, but this affects gas mileage (per manufacturer's tech department).  Any higher compression engine runs hotter, thus the need for a higher octane gas.  

 The test BTW, was rather scientific, 10 memebers drove consistanlty with regular gas for a week, then went to premium for a week, this repeated for a 2 month period.  The gas prices were averaged through this time period to come up with an average price for each type of gas.  No math was needed to determine gas mileage as the cars are equipped with an onboard computer that can calculate gas mileage per your time period requirments.  

I'm not getting into a premium fuel deabte here, the comments were to justify why some engines need high octane fuel, and what the result would be if you didn't use it (no negative results unless you're dealing with a carbeurated, high compression engine).

I also wanted to debunk the notion that premium fuels "sit" longer at the gas station.  they don't.

I never said high octane fuel provided more power or that you "had" to use it.  Do whatever you want with your car, I sure as hell do with mine.  My car will be beat to hell well before any issues from fuel arise I assure you that, I drive it like a race car.....

My cars need 93 oct, but we are only allowed 91 here in Kali. My cars take alot of warm up to work on 91. And they all require that I change the timing and fuel mixtures.

Quoted: Mechanics, while not all in agreement, suggest a number of ways to help protect your vehicle from clogged fuel injectors: Never fill up when tankers are resupplying a service station. This stirs up whatever may be at the bottom of the storage tanks. Keep gas tank as full as possible on a regular basis. Air in the tank contains moisture than can get into gasoline and cause problems. Keep gas tank full or near-full when temperatures drop below freezing. Avoid expensive premium gas because it sits in the tank longer because fewer people buy it.

I call BS on all these old wives tales.  #1 on the list is false.  All gas tanks drain from the bottom, so it doesn't make any difference if you fill up when a tanker is resupplying a gas station ,so sediment at the bottom of the tank is not affected.  However this shouldn't matter because there are gas station fuel filters as well as fuel filters in our cars which get rid of impurities.  Look here to see a sketch of a service station gas tank www.acetank.com/Public/Solutions/ServiceStations/index.cfm?requesttimeout=100 (left menu-Click resources-click technical documents-click on permatanks at the bottom of the page)

#2 is also false Keeping the gas tank full, because air in the tank has moisture, BS.  There is virtually no air in your tank if it is functioning properly.  

Indeed, you will notice when you open your gas cap to refill, you should hear a "wooshing" sound.  That is because there is a vacuum in your gas tank--which means there is virtually no air in your tank.  You will not get any appreciable moisture in the tank, so BS on this one also.

#3 and #4 are also false--WOW, how much conjecture and urban legend can we get in one news story?  Keep your gas tank full in the winter.  WHY?  Is the fuel in your tank gonna freeze?   Do you live on the North Pole?

Premium gas does not sit longer in the service station tanks.  The premium tanks are usually smaller or fewer in number.

Remember to question what you read at all times, guys.

I have to have a minimum of 93 octane in my truck or it will detonate and throw a rod. I have over 10 psi of intercooled boost getting slammed in there.... I only buy from stations with high volume.

My car manual says 86. I usually put in the 85.

I run 93 in the car, it runs better and I get better mileage with it.

I get gas on Sundays since its 10cent off premium

Quoted: Quoted: I'm going to put 87 octane in my Lightning now, becuase this article says that will get me better mileage! Actually, I'd save a hell of a lot of gas money if I blew it up So you spent $30+ k on a high performance truck that gets extreme(for a truck) horsepower.   It has all the cool gismos and doodads that make it look and go fast. Yet you are going to use CHEAPER gas to save fuel economy?? WTF????? ANd this is all based one 1 article? SGtar15

Dude, sarcasm

And no, I didn't pay nearly that much.

Quoted: When I purchased my Land Rover in 1999 it was placarded with warnings to run only 92 octane or greater fuel.  I did this to protect my investement.  Some months later I was reading an australian Land Rover site which said 87 octane or greater.  I asked the service manager at the dealership why the difference?  He said because Americans buying premium cars expect them to run on premium fuel.  He further stated that 87 octane would not hurt the car and I would notice little or no difference.

Did you have a Euro Spec manual?  I think they calculate octane differently in socialist countries.

Just a FYI on Octane boosters.  Save your money on octane booster bottles from pep boy and such.  The amount added to a tank is so small, were talking 10ths of a point.   Its all expensive marketing.

So say then you want to up your octane for whatever reason, add 5 gallons of 100 race gas added to 10 gallons of 91 will net you 94 RON.  Its not half and half and meet in the middle...

My high compression engine needs at least 93 to be happy.  94 when I'm running hard, and race gas at the track (5.50 a gallon).