High Octane
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Burning Brakes
Joined: Dec 2003
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From: Madison Mississippi
High Octane
Anybody know if you really have to use 93 octane wit the LT-1. I understand the knock sensors retard the timing if knock is detected so, why use the 93???I mean it doesn't make sense if you think about it? I always use 93 but, with the high cost these days has left me pondering if there is any true performance based reason. 
Team Owner
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From: Northern, VA
St. Jude Donor '15
"In honor of jpee"
I just read an aritcle yesterday that said, it depends. Today's cars (of which your's is not) have some waffle language. Some owner's manuals say, "Recommend 91, 93, premium, etc." And some say, "requires". That's the difference. Unless I'm wrong, I'd bet your's says, requires both in the book and right next to the gas tank filler.
Race Director
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From: Melbourne Florida
Cruise-In IV Veteran
I agree...my 93 says "requires"...it would probably run on 89 but to save .10 a gallon I'm not foolin with it...when mine was a daily driver I averaged about 25 gallons a week...this means I would have saved about $120 per year...not worth it, imho...
Drifting
Joined: Apr 1999
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From: Middletown New Jersey
If the ECM pulls timing you will be down on power. Drive it around on a lower octane and datalog what the ECM is doing. If it isn't pulling timing, then you don't need premium. If it is and you want the max power potential of your motor, use higher octane.
Race Director
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From: Lake Wylie SC
Let me see if I can give you the short answer. The higher your compression ratio and the more your timing is advanced, the higher the octane needs to be. In the combustion chamber during the compression stroke lower octane fuel will ignite before it is supposed to and explode instead of burning. This gives you detonation. As you step on the pedal, your ECM advances the timing and with lower octane, again the fuel can ignite or explode too soon. If you need to. try the lower octane and stay out of the go fast mode. But if you start hearing that dreaded ping or knock, you better get back on high test. There is a lot more about octane to know, but it will take a course in school to really get to know about it.
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From: Athens AL
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If youre just driving to work at a leisurely pace and arent going to high rpms, then you can run lower octanes, unless you hear the knock.
I wouldnt dare run lower than midgrade on an LT1 in that case though.
The ECM cant protect you from doing something dumb.
I wouldnt dare run lower than midgrade on an LT1 in that case though.
The ECM cant protect you from doing something dumb.
Team Owner
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From: OBAMA IS HITLER
i agree, and the short of it is that all things being equal with a factory c/r rating of 10.5:1 for the "average" LT1, its a close call between 91 and 93 octane. i wouldn't run a lower grade than 91.
try 1/4 tank with 91 and get on it a little when the temps aren'y sky-high outside.....if there's audible ping, there's your answer -- stick with 93.
try 1/4 tank with 91 and get on it a little when the temps aren'y sky-high outside.....if there's audible ping, there's your answer -- stick with 93.
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From: The Top of Utah
The only thing a higher octane provides is increased knock, or detonation suppression. If your ESC is working properly, you will never hear any pinging that might tend to occur. Also, knocking should only happen at WOT or advanced throttle openings. Higher rpms are not a factor. Actually there is a greater risk of knock, if you are lugging the engine. If you don't drive in a manner that is likely to produce knock, you have little to worry about. You can monitor a scanner to see if you are producing any knock counts. If not go to the next lower octane, and do it again. Not only is lower octane gasoline less expensive, it will produce more power, if it doesn't allow knock, or cause retarding of the timing.
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Thread Starter
Burning Brakes
Joined: Dec 2003
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From: Madison Mississippi
Originally Posted by CFI-EFI
The only thing a higher octane provides is increased knock, or detonation suppression. If your ESC is working properly, you will never hear any pinging that might tend to occur. Also, knocking should only happen at WOT or advanced throttle openings. Higher rpms are not a factor. Actually there is a greater risk of knock, if you are lugging the engine. If you don't drive in a manner that is likely to produce knock, you have little to worry about. You can monitor a scanner to see if you are producing any knock counts. If not go to the next lower octane, and do it again. Not only is lower octane gasoline less expensive, it will produce more power, if it doesn't allow knock, or cause retarding of the timing.
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Le Mans Master
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Originally Posted by RUBYREDVETTECARD
Does the lower octane take the knocks out of the parameters or range of knock sensor control?
I am not exactly sure what this question is but.. higher octane fuel is LESS volitile hence not allowing knock to happen. Higher octane has a slower burn rate thus allowing it to work better (less knock) with higher compression. Use the fuel with the LOWEST octane without creating knock.
To answer the first question. If you have access to datamaster run a lower octane gas and see if you get mucho knock counts. I got more knock counts revving the motor when the car wasn't moving. If you drive like a grandma I would suspect you don't even need 91, but you would need to verify if your computer is seeing knock counts (datamaster or equivalent).
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From: OBAMA IS HITLER
Originally Posted by hippy
To answer the first question. If you have access to datamaster run a lower octane gas and see if you get mucho knock counts. I got more knock counts revving the motor when the car wasn't moving. If you drive like a grandma I would suspect you don't even need 91, but you would need to verify if your computer is seeing knock counts (datamaster or equivalent).
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From: The Top of Utah
Originally Posted by hippy
I got more knock counts revving the motor when the car wasn't moving.
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Le Mans Master
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Originally Posted by CFI-EFI
I had a situation similar to that. As a test, I drained the tank and filled it with the best gasoline around. Then I set my base timing to zero. I STILL got knock counts revving the engine in neutral. Since I determined that the car couldn't be knocking under those conditions, I deemed the counts were false counts.
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Funny you say this, I just checked my datamaster from a few dyno pulls and I got 14 counts as the car was being started. I am running 91 octane on these pulls and thruout the pull I only got 25 total counts.
I just checked another run I ran to 100mph (this was after 6 minutes of driving) I only had 20 knock counts. That is very very few. I could either go down on octane or try to advance my timing. I guess what you should look at is how long and how much timing is being pulled out to determine if you need a certain grade of fuel. Getting a car just below knocking is where power is going to be made.
Last edited by hippy; Aug 1, 2005 at 12:23 PM.