Octane tables questions
Thread Starter
Le Mans Master
Joined: Aug 2004
Posts: 5,422
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From: Just moved back to the "old country"
Octane tables questions
Ok, so I have some questions on octane ratings and the octane tables in the computer.
I read somewhere else that when the tank is full the computer waits to sense the octane rating of the gas - that it "starts out" using the lower octane table and if the sensors say the gas is > 93 octane it switches to the higher octane rating tables and adjusts timing etc. Is this true ?? seems wierd if true. Some one mentioned in a thread here or on another forum they noticed their car was faster (SOTP) when the tank ran down a bit and one of the tuners offered this explanation.
also - is there any benefit at the track for a STOCK C6 to run racing gas? Is there anything the octane tables sense for octane ABOVE 93??
I read somewhere else that when the tank is full the computer waits to sense the octane rating of the gas - that it "starts out" using the lower octane table and if the sensors say the gas is > 93 octane it switches to the higher octane rating tables and adjusts timing etc. Is this true ?? seems wierd if true. Some one mentioned in a thread here or on another forum they noticed their car was faster (SOTP) when the tank ran down a bit and one of the tuners offered this explanation.
also - is there any benefit at the track for a STOCK C6 to run racing gas? Is there anything the octane tables sense for octane ABOVE 93??
Racer
Joined: Feb 2005
Posts: 380
Likes: 33
i cant say for sure about the LS2's but with the LS1's its been proven to be FACT that the car runs using a combination of both tables (switches between the 2)....obviously more of the lower one if knock is being detected. Again, i cant say for sure but i doubt the level of fuel in your tank has anything to do with which octane table the PCM uses at any particular time. To get into some real technical discussions go over to LS1tech.com (tuning section), or HPtuners forums.
Racer
Joined: Jul 2004
Posts: 431
Likes: 0
From: Browns Mills NJ
My Experience with the LS1 (and I believe the LS2 is no different) is that the High Octane table is primary source for spark. If the PCM sees high knock intensity, it will revert to the low octane table.
Jersey
Jersey
Le Mans Master
Joined: Jan 2005
Posts: 5,611
Likes: 5
From: Thousand Oaks California
There is no sensor for gasoline octane. The engine contains two (2) knock sensors. If either sensor detects spark knock, the ignition timing is retarded until the spark knock is eliminated.
Racer
Joined: Feb 2005
Posts: 320
Likes: 1
From: San Jose CA
Whether running race gas at the track would be beneficial to a stock C6 depends on the conditions. If you run the car REAL hard and it's a hot day then you may trigger the low octane tables.
From what I've heard, once you trigger the low octane tables, it doesn't revert back to the higher octane table until your next fill up. I'm not positive on this point, one of the experienced tuners could probably step in and explain it better.
I believe the higher octane tables are designed to run with 93 octane. I don't think GM tunes the car for any higher from the factory. However, I'm sure if you get a tuner to mess with your tables a bit you can have it retuned for whatever octane you want (just make sure you keep that much octane quality in the gas you put into it).
From what I've heard, once you trigger the low octane tables, it doesn't revert back to the higher octane table until your next fill up. I'm not positive on this point, one of the experienced tuners could probably step in and explain it better.
I believe the higher octane tables are designed to run with 93 octane. I don't think GM tunes the car for any higher from the factory. However, I'm sure if you get a tuner to mess with your tables a bit you can have it retuned for whatever octane you want (just make sure you keep that much octane quality in the gas you put into it).
Le Mans Master
Joined: Nov 1999
Posts: 7,695
Likes: 51
From: Imperial Beach CA
I had mine tuned with LS2 edit (beta) and everything seemed to go well but after a bit of driving couldn't really tell of any difference any more. Went back in to change intake a month later with an updated version of LS2 edit and we did a base line again. It had reverted back to the original HP numbers. When the data was evaluated it was found we were in the Low Octane table. Tuning that out HP went back to the original tuned numbers. So they just eliminated the low octane table. I do notice when driving in heavy SLOW traffic for an extended period of time in hot weather that there is a bit of ping rattle when you hit the throttle.
Racer
Joined: Feb 2005
Posts: 320
Likes: 1
From: San Jose CA
Originally Posted by jimman
I had mine tuned with LS2 edit (beta) and everything seemed to go well but after a bit of driving couldn't really tell of any difference any more. Went back in to change intake a month later with an updated version of LS2 edit and we did a base line again. It had reverted back to the original HP numbers. When the data was evaluated it was found we were in the Low Octane table. Tuning that out HP went back to the original tuned numbers. So they just eliminated the low octane table. I do notice when driving in heavy SLOW traffic for an extended period of time in hot weather that there is a bit of ping rattle when you hit the throttle.
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Le Mans Master
Joined: Nov 1999
Posts: 7,695
Likes: 51
From: Imperial Beach CA
Originally Posted by Virt
I was thinking about that. How dangerous is it to remove the low octane tables completely? It really sucks cuz in CA we only get 91 octane which I'm sure doesn't help us stay in the higher table
Racer
Joined: Feb 2005
Posts: 320
Likes: 1
From: San Jose CA
Originally Posted by jimman
Only seems to rattle if I'm in LA traffic for an hour or so with temps in the 90's other than that it just halls AAAs with no apparent problems. It rattled bad on particular day and I stopped at the 76 in Orange County and got stiffed for two gallons of 100 octane at $6.30 a gallon. Went away immediately.
That's why I've been trying to hard to find a 76 that'll pump 100