Timing Tables and 87-93 Octane Fuel
08-31-2009, 08:44 PM
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Timing Tables and 87-93 Octane Fuel So I have been looking through past posts and searching google, but I am not sure I completely understand how this car works. The engine is intended to run on a higher octane fuel, but from what I have seen with many other cars with a high compression ratio engine, 91+ octane is suggested by not necessary. And the owner's manual even mentions a loss of horsepower when using a lower octane.
So how exactly does it work with the LS1 and other engines with high compression ratio? Does the ECU have multiple timing tables that it uses based on the fuel? Will the timing automatically be adjusted to the correct timing when a different octane is detected?
How does it determine what octane is being used? Is this all really only controlled by the knock sensor? Does the timing change only when the knock sensor detects pinging or detonation?
Also, can an engine with a compression ratio of 10.5:1 run best on 87 octane, and there be no advantage to using a higher octane?
Sorry for all the questions. I am just trying to understand these high compression engines and how they adjust properly for different octane fuel.
So how exactly does it work with the LS1 and other engines with high compression ratio? Does the ECU have multiple timing tables that it uses based on the fuel? Will the timing automatically be adjusted to the correct timing when a different octane is detected?
How does it determine what octane is being used? Is this all really only controlled by the knock sensor? Does the timing change only when the knock sensor detects pinging or detonation?
Also, can an engine with a compression ratio of 10.5:1 run best on 87 octane, and there be no advantage to using a higher octane?
Sorry for all the questions. I am just trying to understand these high compression engines and how they adjust properly for different octane fuel.
08-31-2009, 10:40 PM
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On a stock tune it will sense knock and pull timing to the lower tables. After fueling it will go back to the higher tables until it senses knock again.......repeat...... All bets are off on this with an aftermarket tune. I will ask this question next time i bump into my tuner....
09-01-2009, 09:13 AM
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If you are talking about the 2002 LS1..
There are two Timing Tables..A High-Octane Table, and a Low Octane Table. Each have a different set of timing values. "The PCM interpolates between the high-octane table and low-octane depending on knock activity..EFILive."
However, depending on your knock sensors to determine your spark timing and whether you have adequate fuel octane is not always the best strategy. It really is meant to prevent detonation from the occasional bad tank of fuel or overly aggressive spark timing. So, it is all dependent on your knock sensors working flawlessly and it pulls timing after knock is sensed.
My personal advice is to run the highest quality gasoline you can find and stick with the highest octane you can find. Most of the octane debates center around the effectiveness of seeking out 93+ octane fuel. You might not see a benefit there.
Unless you are pinching pennies, IMO go with a high quality 93 Octane rated fuel for your vehicle, especially if modded. Most people can still run 93 Octane up to ~ 11.0:1 CR.
Hope that helps.
..WeathermanShawn..
There are two Timing Tables..A High-Octane Table, and a Low Octane Table. Each have a different set of timing values. "The PCM interpolates between the high-octane table and low-octane depending on knock activity..EFILive."
However, depending on your knock sensors to determine your spark timing and whether you have adequate fuel octane is not always the best strategy. It really is meant to prevent detonation from the occasional bad tank of fuel or overly aggressive spark timing. So, it is all dependent on your knock sensors working flawlessly and it pulls timing after knock is sensed.
My personal advice is to run the highest quality gasoline you can find and stick with the highest octane you can find. Most of the octane debates center around the effectiveness of seeking out 93+ octane fuel. You might not see a benefit there.
Unless you are pinching pennies, IMO go with a high quality 93 Octane rated fuel for your vehicle, especially if modded. Most people can still run 93 Octane up to ~ 11.0:1 CR.
Hope that helps.
..WeathermanShawn..
