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Discussion Starter · #1 ·
OK, so the premium fuel is recommended. But the Sky will run on 87 octane. If you dump premium fuel into it, you will get more power than the 87 octane.

My question is, how does the engine know which fuel is in the car to then make whatever adjustments are required for that particular fuel?

Could you get by with mid range octane with a marginal amount of additional power, or does it have to be the real expensive stuff or nothing?
 

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Your cars computer (ECU) makes the necessary adjustments in timing to compensate for the lower octane fuel. Some cars that require premium fuel will make a knocking noise using 87 octane because of compression ratios and in that scenario the ECU can only do so much.
 

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dmbdlatc said:
OK, so the premium fuel is recommended. But the Sky will run on 87 octane. If you dump premium fuel into it, you will get more power than the 87 octane.

My question is, how does the engine know which fuel is in the car to then make whatever adjustments are required for that particular fuel?

Could you get by with mid range octane with a marginal amount of additional power, or does it have to be the real expensive stuff or nothing?
lets just say it only costs you from 2 to 3 dollars a tankfull more for premimum over regular. so it goes to how much you want to spend for better performance, i say try each grade for 5 tankfulls each, and see what the seat of the pants tells you, If your driving style makes no difference in the performance i would say go with whatever grade you want. but if you are the type that wants the most you can get available at any time then get the permimum....
 

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Discussion Starter · #4 ·
SaturnSkyDude said:
Your cars computer (ECU) makes the necessary adjustments in timing to compensate for the lower octane fuel. Some cars that require premium fuel will make a knocking noise using 87 octane because of compression ratios and in that scenario the ECU can only do so much.
Thank you, but that tells me WHAT it does. I am more curious as to HOW IT KNOWS to do, what it does? What sensors, or whatever, does the ECU uses to determine what to do?
 

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from http://www.innovatemotorsports.com/resources/ecu-basics.php

Electronic engine management is all about getting accurate information from the engine’s environment and then sending out accurate signals to the control mechanisms of the engine. In a typical system you have the following input sensors:

1. throttle position of the accelerator
2. air temperature in the intake manifold
3. air pressure (or weight of the air) in the intake manifold
4. a measure of the residual oxygen in the exhaust manifold (the O2 sensor)
5. engine rpm
6. camshaft position
7. crankshaft position
8. engine load, usually as a function of manifold vacuum pressure
9. engine coolant temperature

From me:

The engine doesn't "know" it's burning lower octane fuel. Gasoline engines will run on any grade of gasoline you feed them. Too low an octane rating can also cause damage from "knocking" (uneven leading edge of burning fuel coming into contact with the piston). I don't believe the ECU will magically increase the performance potential of low octane fuel.
 

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I believe it has sensors that detect the noise created by knock going on. It then retards the timing till no more pinging is detected.
 

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brentil said:
I believe it has sensors that detect the noise created by knock going on. It then retards the timing till no more pinging is detected.
Isn't it more likely that the ECU takes the readings from residual oxygen in the exhaust manifold (the O2 sensor), detects inefficient combustion and retards the timing?
 

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Not to complicate matters, but...

The FlexFuel (E85 compatible) engines DO have sensors that detect what kind of fuel (percentage of ethanol) is in the tank and adjust the engine combustion parameters accordingly.

Sky engines are not FlexFuel compatible, however.
 

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I think Brentil is correct. That's a common method used on two stroke snowmobile engines. The technology is proven and it works well.

I tried 87 octane in my Sky and it runs fine, with no spark knock or detonation at all. If the Sky didn't advance the timing when running premium, there would be no HP gain. It's compression and ignition timing that make HP, not octane. premium fuel allows more timing advance without detonation.
 

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Sky Hi said:
I think Brentil is correct. That's a common method used on two stroke snowmobile engines. The technology is proven and it works well.

I tried 87 octane in my Sky and it runs fine, with no spark knock or detonation at all. If the Sky didn't advance the timing when running premium, there would be no HP gain. It's compression and ignition timing that make HP, not octane. premium fuel allows more timing advance without detonation.
Can you provide a link to information about this audio based technology? I can't find anything about it.

Octane is just a measure of the amount of compression that a fuel will stand without spontaneously igniting (without a spark) from the pressure alone.

Premium fuel (high octane) is used in higher compression engines because the pressure at which it spontaneously ignites is higher than regular.

You are right. Octane doesn't increase HP. Putting high octane fuel in a car that does not require it does nothing to enhance performance, so this whole concept of the ECU somehow compensating for the octane rating makes no sense. Any octane rating at or above the manufacturer 's minimum requirment will burn just fine without knocking or pinging or spontaneously igniting within the combustion chamber.

The compression ratio of the engine does not change unless you have some magical way of dynamically altering the basic physics of how the air/fuel mixture is compressed within the combustion chamber (changing the diameter of the cylinders or stroke of the pistons, for example).
 

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In the old days before computers and sensors, we used to make sure you were burning the type of fuel you would normally use when getting a "tune-up" which included setting the timing which was not "automagically" advanced or retarded as needed. Some habits die hard, I still do that....
 

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I remember LT1's with header installs would get huge knock on 87... throw a LT4 knock sensor in and it will help you with those cars.

But like said above, 13.9 gallon tank say 87 is at $3=$41.70 and 91 at $3.20=$44.48....

:)
 

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ggccg said:
Can you provide a link to information about this audio based technology? I can't find anything about it.

Octane is just a measure of the amount of compression that a fuel will stand without spontaneously igniting (without a spark) from the pressure alone.

Premium fuel (high octane) is used in higher compression engines because the pressure at which it spontaneously ignites is higher than regular.

You are right. Octane doesn't increase HP. Putting high octane fuel in a car that does not require it does nothing to enhance performance, so this whole concept of the ECU somehow compensating for the octane rating makes no sense. Any octane rating at or above the manufacturer 's minimum requirment will burn just fine without knocking or pinging or spontaneously igniting within the combustion chamber.

The compression ratio of the engine does not change unless you have some magical way of dynamically altering the basic physics of how the air/fuel mixture is compressed within the combustion chamber (changing the diameter of the cylinders or stroke of the pistons, for example).
http://www.wellsmfgcorp.com/counterpoints/counterp_v4_i4_2000.pdf
I learned a long time ago Before fuel injection and Computer controls that if you run a higer octane fuel you can advance your timing higher and increase performance, that is part of what the ecm does, It Detects the higest amount of timing advance your car can use without Knocking, this will give you better performance, it can sense a knock your ear cannot detect and retards the timing before you even know it, another thing the ECM does is it can adjust the amount of fuel and the length of spark to get the best burn, it uses the other sensors on the engine to get the best performance available depending on what fuel you use.
 

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SkyMan 07 said:
http://www.wellsmfgcorp.com/counterpoints/counterp_v4_i4_2000.pdf
I learned a long time ago Before fuel injection and Computer controls that if you run a higer octane fuel you can advance your timing higher and increase performance, that is part of what the ecm does, It Detects the higest amount of timing advance your car can use without Knocking, this will give you better performance, it can sense a knock your ear cannot detect and retards the timing before you even know it, another thing the ECM does is it can adjust the amount of fuel and the length of spark to get the best burn, it uses the other sensors on the engine to get the best performance available depending on what fuel you use.
Thanks for the link :) .

I understand what you are saying and agree, but all of that is just fine tuning. Minor changes to the spark timing and the intensity or duration of the spark make for more efficient burning of the fuel and even 87 octane gasoline will benefit from this provided the compression of the engine does not exceed the octane rating of the fuel. The ECU is just constantly fine tuning the engine to get the best from whatever grade of gasoline you use that is within the octane range of the engine.

93 Octane gasoline does not burn more intensely or smoother or create more power than 87 Octane gasoline. All it does is stand more compression before igniting. Unless you can increase compression, the higher octane fuel doesn't gain you anything.

The original question here was "how does the engine know what grade of fuel you use." The answer is that it doesn't and it couldn't care less as long as it meets the minimum octane rating so that the fuel doesn't spontaneously ignite under normal operating conditions. After that, it's all just a matter of constant fine tuning by the ECU.
 

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ggccg said:
Thanks for the link :) .

I understand what you are saying and agree, but all of that is just fine tuning. Minor changes to the spark timing and the intensity or duration of the spark make for more efficient burning of the fuel and even 87 octane gasoline will benefit from this provided the compression of the engine does not exceed the octane rating of the fuel. The ECU is just constantly fine tuning the engine to get the best from whatever grade of gasoline you use that is within the octane range of the engine.

93 Octane gasoline does not burn more intensely or smoother or create more power than 87 Octane gasoline. All it does is stand more compression before igniting. Unless you can increase compression, the higher octane fuel doesn't gain you anything.

The original question here was "how does the engine know what grade of fuel you use." The answer is that it doesn't and it couldn't care less as long as it meets the minimum octane rating so that the fuel doesn't spontaneously ignite under normal operating conditions. After that, it's all just a matter of constant fine tuning by the ECU.
let me try this again, The engine does not know what grade or octane fuel you are using, The computer monitors all the engines parameters and adjusts all it can accordingly to get the best performance out of any octane fuel you use.. Air, mixture, valve timing.. there is no simple way to answer your question, You would have to be an engineer to understand how it works...
 

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SkyMan 07 said:
let me try this again, The engine does not know what grade or octane fuel you are using, The computer monitors all the engines parameters and adjusts all it can accordingly to get the best performance out of any octane fuel you use.. Air, mixture, valve timing.. there is no simple way to answer your question, You would have to be an engineer to understand how it works...
It wasn't my question and I agree with what you said... which is what I said all along... the engine does not know anything about the grade of fuel... it just does the best it can with what you give it.

Somebody else along the way introduced the idea that higher octane fuel gives you higher compresssion and more horsepower. I dispute that.
 

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ggccg said:
It wasn't my question and I agree with what you said... which is what I said all along... the engine does not know anything about the grade of fuel... it just does the best it can with what you give it.

Somebody else along the way introduced the idea that higher octane fuel gives you higher compresssion and more horsepower. I dispute that.
Well I don't think that is the case, it is just that the car was designed to perform best with 93 octane fuel but it will not harm the engine to run 87, it will just lose some performance because of the adjustments the computer makes so there will be no Knocking to harm the engine.
 

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I'm pretty sure it is some sort of audio sensor that listens for ping.
 

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brentil said:
I'm pretty sure it is some sort of audio sensor that listens for ping.
you are sort of correct, they are vibration sensors tuned to the frequency of vibrations that occur during the ping or knock... but they are much more sensitive than the ear or a microphone, so it detects the knock earlier and faster...
 
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