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Valentine One Radar Detector

swamprat
06-17-2007, 01:02 AM
I have heard on a Saturday afternoon auto mechanic talk show that even with the computer controlled engines, it can still be better to run higher octane gas. Their contention is that low octane gas doesn't burn as evenly as mid grade or super. That causes the knock sensors to retard the timing of the engine, and then the fuel will eventually leave carbon deposits on the pistons.

I'm not sure about the validity of that claim, but I have noticed a smoother idle when I put the Plus in the tank. While more expensive, 10-12 cents per gallon- it makes little difference in a $3.00-3.50 fill up. I stopped caring about the difference in plus versus regular when gas hit 2 bucks.

Comments?

DonTom
06-17-2007, 08:53 AM
"I'm not sure about the validity of that claim"

Many car owner's manuals (does anybody else read them besides me?) Say do NOT use higher than the 87 octane and they give two reasons. One is it's a waste of money and the other is that the knock sensors may not work correctly with higher octane gasolines. Vehicles that are designed for 87 octane assume you will use 87 octane and other grades should only be used when the 87 is not available.

Nevertheless, no doubt using too high of an octante is safer than too low.

-Don-

Eric
06-17-2007, 09:06 AM
I have heard on a Saturday afternoon auto mechanic talk show that even with the computer controlled engines, it can still be better to run higher octane gas. Their contention is that low octane gas doesn't burn as evenly as mid grade or super. That causes the knock sensors to retard the timing of the engine, and then the fuel will eventually leave carbon deposits on the pistons.

I'm not sure about the validity of that claim, but I have noticed a smoother idle when I put the Plus in the tank. While more expensive, 10-12 cents per gallon- it makes little difference in a $3.00-3.50 fill up. I stopped caring about the difference in plus versus regular when gas hit 2 bucks.

Comments?


A modern car's ECM can adjust for lower-than-specified octane, but if the engine was designed to operate on unleaded premium that is the fuel you should use to obtain peak power/MPGs.

Conversely, it serves no purpose to use higher octane fuel in an engine designed for lower octane fuel - and may degrade performance/MPGs since the hgh octane fuel isn't designed to burn efficiently in an engine designed to run on lower octane fuel.

mrblanche
06-17-2007, 10:35 AM
I have heard on a Saturday afternoon auto mechanic talk show that even with the computer controlled engines, it can still be better to run higher octane gas. Their contention is that low octane gas doesn't burn as evenly as mid grade or super. That causes the knock sensors to retard the timing of the engine, and then the fuel will eventually leave carbon deposits on the pistons.

I'm not sure about the validity of that claim, but I have noticed a smoother idle when I put the Plus in the tank. While more expensive, 10-12 cents per gallon- it makes little difference in a $3.00-3.50 fill up. I stopped caring about the difference in plus versus regular when gas hit 2 bucks.

Comments?


Higher-than necessary octane will cause deposits on your valves and other problems. Use the lowest grade approved for your engine. Anyone who says otherwise probably owns oil stocks.

chiph
06-17-2007, 01:28 PM
Conversely, it serves no purpose to use higher octane fuel in an engine designed for lower octane fuel - and may degrade performance/MPGs since the hgh octane fuel isn't designed to burn efficiently in an engine designed to run on lower octane fuel.


I find I have to run mid-grade in the summer. There's this one hill on I-40 that on hot summer days with the A/C running, the engine will knock when going up it when running standard grade.
YMMV.

Chip H.

DonTom
06-17-2007, 09:21 PM
"Higher-than necessary octane will cause deposits on your valves and other problems."

Is that because of the fact that it explodes at a higher temperature?

-Don-

DonTom
06-17-2007, 09:29 PM
"There's this one hill on I-40 that on hot summer days with the A/C running, the engine will knock when going up it when running standard grade."

Some owner's manuals say that you should ignore light knocking under such conditions (in newer ECM controlled cars, but not in older vehicles), as the knock sensors should retard the timing to a safe area and you will get maximum MPG, efficiency and performance with the light knocking.

Severe knocking means you have another problem. You should never have to use a higher octane than the car is designed for.

-Don-

chiph
06-17-2007, 09:59 PM
It is light knocking, but I still don't like to hear it. Especially when I can make it go away so simply.

The conditions are: Uphill, A/C on, 90F+ temps, 75mph+, so it's a heavy load & understandable that it would want to knock.

Chip H.

DonTom
06-17-2007, 11:40 PM
"It is light knocking, but I still don't like to hear it. Especially when I can make it go away so simply."

Your still thinking about the old days. Old habits are hard to break. Have you read your owner's manual to see what it says about light knocking in extreme conditions? Read your owner's manual and see what it says about it under "fuel requirements".

BTW, is this vehicle a stick shift? If so, I would simply keep the RPM's up and that should stop the knocking the correct way.

-Don-

Jim Rose
07-01-2007, 12:39 PM
"Higher-than necessary octane will cause deposits on your valves and other problems."

Is that because of the fact that it explodes at a higher temperature?

-Don-




High octane gas burns at a slower rate than low octane gas. The object of the whole sequence inside the engine is to have a complete burn-- NOT EXPLOSION-- during the power stroke. So, the ignition timing should set the burn off at some point before the piston reaches top dead center and the burn should be complete after TDC just as the exhaust valve starts to open.
If you start the burn early because of timing too far advanced, you will get detonation. If the octane of the fuel is too low for the compression of the engine, you will get detonation. Pre-ignition is caused by the after effect of detonation when the cylinder develops hot spots.
Using a fuel of a higher octane than the manufacturer requires is a waste of money. It will cause no harm to the engine, but it simply is a waste of money and you possibly will not develop the power as you would with the proper octane fuel.
The computer on most engines will retard the timing if the knock sensor tells it to. Some will have the latitude to make the necessary adjustment. Some will need a higher octane fuel to eliminate the detonation.
The oil companies would love for you to waste your money on their premium grade-- at 30 cents a gallon higher price, a 20 gallon fill up can cost you 6 bucks extra. That's a lot of wasted money over the life of a vehicle!

swamprat
07-01-2007, 10:05 PM
"Higher-than necessary octane will cause deposits on your valves and other problems."

Is that because of the fact that it explodes at a higher temperature?

-Don-




High octane gas burns at a slower rate than low octane gas. The object of the whole sequence inside the engine is to have a complete burn-- NOT EXPLOSION-- during the power stroke. So, the ignition timing should set the burn off at some point before the piston reaches top dead center and the burn should be complete after TDC just as the exhaust valve starts to open.
If you start the burn early because of timing too far advanced, you will get detonation. If the octane of the fuel is too low for the compression of the engine, you will get detonation. Pre-ignition is caused by the after effect of detonation when the cylinder develops hot spots.
Using a fuel of a higher octane than the manufacturer requires is a waste of money. It will cause no harm to the engine, but it simply is a waste of money and you possibly will not develop the power as you would with the proper octane fuel.
The computer on most engines will retard the timing if the knock sensor tells it to. Some will have the latitude to make the necessary adjustment. Some will need a higher octane fuel to eliminate the detonation.
The oil companies would love for you to waste your money on their premium grade-- at 30 cents a gallon higher price, a 20 gallon fill up can cost you 6 bucks extra. That's a lot of wasted money over the life of a vehicle!


Agreed, at least until that time when you engine performs better on the higher octane stuff. With 137,000 miles on my Saturn, I have made the switch to plus since it smoothes out my idle. I suspect that there is some carbon buildup on my valves or my pistons. As far as the cost, 30 cents means little when we are getting raped by specualtors in the oil market to the tune of three bucks a gallon. Gasoline inventories down, price of oil up. Refinery utilization down, oil prices up. The whole thing makes no sense.

Jim Rose
07-02-2007, 01:27 AM
>>I have made the switch to plus since it smoothes out my idle. <<

Obviously the compression of your engine is higher due to the carbon build-up at that mileage!