Ok, probably a simple question that has an easy answer. I have a 97' 4.6L with 147,000. Since she is getting the miles on her and I found out that the valves are leaking a little bit. I wanted to know the pro's and con's (if any) on putting the higher octane fuel in the tank. I know the book says NO, and a friend says with the valves leaking the higher octane could make the engine run worse, so.........................there you go.

Any input on this would be great!

Thanks.

 

Valves leaking? You mean low on compression or guide seals?

 

Higher octane gas only allows you to run more timing and/or boost without detonation. Higher octane fuels generally have a lower BTU rating than lower octane fuels and therefore will produce less power with the same timing.

In your case, the additional octane will not help.

-Don

 

I believe the higher octane burns longer, in any case, the result is burnt valves if you're not properly tuned for it.

 

Yes, I have been told the seals are leaking, due to smoke coming out of the exhaust.

But the thing I asked about the higher octane was at 87' I was getting a sparkplug knock, all the time, and I tried, adding injection cleaner, and tried other stuff, now with the 93' i'm not at all, go figure that one.

So basicly, I'm just tearing it up with the higher octane?

Swell.

HELP!

 

If you need higher octane to combat detonation, use it. You aren't causing any additional harm to the engine.

Greater resistance to knocking, pinging, and pre-detonation is the reason for higher octane.

Of course, there are probably issues with your engine that is leading to the noise, the higher octane is a way to get around the problem.

Steve

 

Are you sure your plugs haven't come loose and are knocking in the holes? There have been plenty of engines with blown plugs and the first sign is a knocking coming from the engine compartment. I would check the plugs and make sure that none of them are loose.

-Don

 

With the amount of pressure in the Combustion Chamber a loose plug will not stay loose for very long before it blows out. If you are needing higher octane to eliminate ping than you most likely have carbon build up in the combustion chamber. Which could lead to leaking valves.

Regards

Jean Marc Chartier

 

I actually missed the part about not getting a knock with 93 octane. If that is the case, then use it. As JMC has already pointed out, you are probably getting detonation due to carbon buildup.

-Don

 

Hi bmc25; A rule of the for us yankees; is the higher the octane the higher the flash point. Hi octane dose not help the starting in cold weather.Because of the higher flash point.So if you are having trouble in warn weather,you have an other problem..Look for bad wires,bad coils,or just plain carbon build up. a tip to find bad wires,is have someone rev up the motor while you look under the hood.in the dark If bad wires are present the engine compartment should look like a lighting storm going on in there. Check the easyest thing first, good luck oldgray

 

Higher octane fuel doesn't burn any hotter than lower octane. If that were the case it would cause detonation. Higher octane fuel has more resistance to break down into elements that can start the combustion process from the heat in the cylinder, and not a controlled spark.

Higher octane fuel has the same flame front speed as lower octane, there are slight differences, however they are too small to even be a factor.

Gasoline when vaporized/heated starts to degrade into seperate flammable elements, including free Hydrogen, and elements containing Hydrogen. These can burn with much less heat to start them off. What happens in the cylinder is as this uncontrolled flame front burns, it creates more heat in the cylinder, causing the remaing fuel to degrade and auto ignite, the gasses create more pressure as they expand,and are compressed by the piston. More pressure, makes more heat, and the visous cycle continues. Detonation.

High octane fuels have stronger(chemical) Hydrogen bonds, and don't give up free Hydrogen as easily. And they resist breaking down. Heat can come from compression, left over spent gasses, even a burr or piece of carbon on the head or on a piston.

In colder climates fuel is blended differently than summer months for better cold performance.

 

Everything you need to know and then some.

http://www.grapeaperacing.com/GrapeA...fueloctane.cfm

 

Hey thanks for the help. I'll be checking everything like you told me too. Love the pics.

Thanks again.

 

The Low-Down on High Octane Gasoline

Are you tempted to buy a high octane gasoline for your car because you want to improve its performance? If so, take note: the recommended gasoline for most cars is regular octane. In fact, in 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. Your best bet: listen to your owner’s manual.

The only time you might need to switch to a higher octane level is if your car engine knocks when you use the recommended fuel. This happens to a small percentage of cars.

Unless your engine is knocking, buying higher octane gasoline is a waste of money, too. Premium gas costs 15 to 20 cents per gallon more than regular. That can add up to $100 or more a year in extra costs. Studies indicate that altogether, drivers may be spending hundreds of millions of dollars each year for higher octane gas than they need.

What are octane ratings?
Octane ratings measure a gasoline’s ability to resist engine knock, a rattling or pinging sound that results from premature ignition of the compressed fuel-air mixture in one or more cylinders. Most gas stations offer three octane grades: regular (usually 87 octane), mid-grade (usually 89 octane) and premium (usually 92 or 93). The ratings must be posted on bright yellow stickers on each gasoline pump.

What’s the right octane level for your car?
Check your owner’s manual to determine the right octane level for your car. Regular octane is recommended for most cars. However, some cars with high compression engines, like sports cars and certain luxury cars, need mid-grade or premium gasoline to prevent knock.

How can you tell if you’re using the right octane level?
Listen to your car’s engine. If it doesn’t knock when you use the recommended octane, you’re using the right grade of gasoline.

Will higher octane gasoline clean your engine better?
As a rule, high octane gasoline does not outperform regular octane in preventing engine deposits from forming, in removing them, or in cleaning your car’s engine. In fact, the U.S.

Environmental Protection Agency requires that all octane grades of all brands of gasoline contain engine cleaning detergent additives to protect against the build-up of harmful levels of engine deposits during the expected life of your car.

Should you ever switch to a higher octane gasoline?
A few car engines may knock or ping — even if you use the recommended octane. If this happens, try switching to the next highest octane grade. In many cases, switching to the mid-grade or premium-grade gasoline will eliminate the knock. If the knocking or pinging continues after one or two fill-ups, you may need a tune-up or some other repair. After that work is done, go back to the lowest octane grade at which your engine runs without knocking.

Is knocking harmful?
Occasional light knocking or pinging won’t harm your engine, and doesn’t indicate a need for higher octane. But don’t ignore severe knocking. A heavy or persistent knock can lead to engine damage.

Is all "premium" or "regular" gasoline the same?
The octane rating of gasoline marked "premium" or "regular" is not consistent across the country. One state may require a minimum octane rating of 92 for all premium gasoline, while another may allow 90 octane to be called premium. To make sure you know what you’re buying, check the octane rating on the yellow sticker on the gas pump instead of relying on the name "premium" or "regular."

 

That's true, and my experience is you always get worse gas mileage with the winter fuel, at least the winter fuel here in NH.

In the spring and summer I avg. approx 18 - 20mpg, in winter I avg. approx. 16 - 18mpg.