How Important is Octane to the C6?
Thread Starter
Instructor
Joined: Oct 2006
Posts: 126
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From: London Ontario
How Important is Octane to the C6?
This is my first post and I'm looking for some expert opinions. I took my 05 C6 4A F55 Ragtop to the track after a good 10 000km break-in. I wanted a a baseline before I started any mods. I even went with 87 octane fuel. It launched decent with a 2.0 60ft, 83 mph 1/8 th, and a 13.43 @ 105.8. I tried shifting on my own, but the tranny seemed to be getting confused and did its own thing. My best run was in drive and let the car do the shifting. Traction was set to competitive mode. I was expecting to crack into the twelves with a better mph. I haven't played with computerized cars much but have been sucessfull running reliable 12 sec carburated daily drivers. Does this engine really need the octane? (It was a cool evening) Or is this what I should expect. For $80,000 canadian I thought I was buying a 12 second daily driver.
Thanks in advance for any replies.
Thanks in advance for any replies.
Last edited by Angelo C6; Oct 8, 2006 at 01:28 PM.
Race Director
Joined: Oct 2004
Posts: 10,089
Likes: 14
Originally Posted by Angelo C6
This is my first post and I'm looking for some expert opinions. I took my 05 C6 4A S55 Ragtop to the track after a good 10 000km break-in. I wanted a a baseline before I started any mods. I even went with 87 octane fuel. It launched decent with a 2.0 60ft, 83 mph 1/8 th, and a 13.43 @ 105.8. I tried shifting on my own, but the tranny seemed to be getting confused and did its own thing. My best run was in drive and let the car do the shifting. Traction was set to competitive mode. I was expecting to crack into the twelves with a better mph. I haven't played with computerized cars much but have been sucessfull running reliable 12 sec carburated daily drivers. Does this engine really need the octane? (It was a cool evening) Or is this what I should expect. For $80,000 canadian I thought I was buying a 12 second daily driver.
Thanks in advance for any replies.
]
Thanks in advance for any replies.
]
The stock tune assumes a minimum octane of 91. The ECM will use knock sensor data to jump to the low octane tables and retard the timing if the octane is lower. The car will stay in the low octane mode until the next fill up.
Note that this is dependent on altitude. At high altitude, 87 octane may not cause the ECM to jump to the low octane tables. At near sea level on a warm day, you may need to run 93 octane fuel to avoid jumping to the low octane tables. So use high octane fuel if you want maximum performance.
The ECM may also pull timing, dynamically, if engine coolant temperature exceeds 200 F, or if IAT exceeds 80 F. This is different from the jump to the low octane tables in that it will correct itself immediately when the temperatures fall rather than waiting for the next fill up. Using higher octane fuel won't affect this behavior.
So to answer your question, yes the engine really needs premium fuel to develop maximum power.
Race Director
Joined: Apr 1999
Posts: 12,735
Likes: 28
From: Kayenta Utah
93 octane is "recommended" for the LS2. (It's "required" for the Z06.) If you ran 87 octane, the knock sensor pulled timing out at higher rpms, sapping you of horsepower. Your ET wasn't bad, but speed looks to be down. Also, what elevation did you run at? Sea level produces the baseline numbers. http://www.gnttype.org/techarea/misc/altitude.html
Team Owner
Joined: Oct 2004
Posts: 27,420
Likes: 64
From: San Clemente CA
Originally Posted by shopdog
You'll get pretty aggressive timing retard on 87 octane gas (with a corresponding reduction in engine power). Expect to lose at least 20 hp when running 87 octane fuel, likely more than that.
The stock tune assumes a minimum octane of 91. The ECM will use knock sensor data to jump to the low octane tables and retard the timing if the octane is lower. The car will stay in the low octane mode until the next fill up.
Note that this is dependent on altitude. At high altitude, 87 octane may not cause the ECM to jump to the low octane tables. At near sea level on a warm day, you may need to run 93 octane fuel to avoid jumping to the low octane tables. So use high octane fuel if you want maximum performance.
The ECM may also pull timing, dynamically, if engine coolant temperature exceeds 200 F, or if IAT exceeds 80 F. This is different from the jump to the low octane tables in that it will correct itself immediately when the temperatures fall rather than waiting for the next fill up. Using higher octane fuel won't affect this behavior.
So to answer your question, yes the engine really needs premium fuel to develop maximum power.
The stock tune assumes a minimum octane of 91. The ECM will use knock sensor data to jump to the low octane tables and retard the timing if the octane is lower. The car will stay in the low octane mode until the next fill up.
Note that this is dependent on altitude. At high altitude, 87 octane may not cause the ECM to jump to the low octane tables. At near sea level on a warm day, you may need to run 93 octane fuel to avoid jumping to the low octane tables. So use high octane fuel if you want maximum performance.
The ECM may also pull timing, dynamically, if engine coolant temperature exceeds 200 F, or if IAT exceeds 80 F. This is different from the jump to the low octane tables in that it will correct itself immediately when the temperatures fall rather than waiting for the next fill up. Using higher octane fuel won't affect this behavior.
So to answer your question, yes the engine really needs premium fuel to develop maximum power.
Thread Starter
Instructor
Joined: Oct 2006
Posts: 126
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From: London Ontario
Great, thanks for the quick response. I have run low compression cars that actually ran better with 87 octane (69 Firebird) others needed 94 (81 GP). What do you find works best, 87 with an additive or high octane 94 pump gas? Ball park, how much do you think I hurt my ET. as far as seal level, I don't know. I'm in London, Ontario, in the middle of all the great lakes.
Le Mans Master
Joined: Jul 2005
Posts: 5,328
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Originally Posted by VET4LES
I'm curious about how it knows when you fill it up, or does the knock sensor recognize higher octane?
Thread Starter
Instructor
Joined: Oct 2006
Posts: 126
Likes: 0
From: London Ontario
I think you are right. After my poor timeslip. I added some octane boost and 10 litres of gas. I went for a short drive and the there was a noticable difference. The car actually broke free in second gear.
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Race Director
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Originally Posted by Angelo C6
Great, thanks for the quick response. I have run low compression cars that actually ran better with 87 octane (69 Firebird) others needed 94 (81 GP).
What do you find works best, 87 with an additive or high octane 94 pump gas?
Ball park, how much do you think I hurt my ET. as far as seal level, I don't know. I'm in London, Ontario, in the middle of all the great lakes.
Drifting
Joined: Jul 2005
Posts: 1,343
Likes: 1
From: CA
Originally Posted by VET4LES
I'm curious about how it knows when you fill it up, or does the knock sensor recognize higher octane?