L46 and lower octane
Melting Slicks
Joined: Feb 2004
Posts: 2,111
Likes: 32
From: Damascus MD
Ping
I had detonation issues after my carb was just rebuilt by Lars and set my timing to 34° all in when I was running 10% 93 octane. I had about a 1/4 of a tank of gas. I went to my local ethanol-free station and filled up with 93 octane and went through about 1/2 a tank that afternoon - by the end of the day no ping.
Now, I will let others debate that the ethanol was the cause of my detonation problems, but until I hear otherwise, I felt that the ethanol was the issue.
Now, I will let others debate that the ethanol was the cause of my detonation problems, but until I hear otherwise, I felt that the ethanol was the issue.
I may experiment with adjusting the carb to run a little richer since it would be nice to run well on 93 pump gas.
I still suspect it will run best on straight up 110 real gas without the ethanol. It really runs for what it is, on the good stuff!
Bill
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
I had detonation issues after my carb was just rebuilt by Lars and set my timing to 34° all in when I was running 10% 93 octane. I had about a 1/4 of a tank of gas. I went to my local ethanol-free station and filled up with 93 octane and went through about 1/2 a tank that afternoon - by the end of the day no ping.
Now, I will let others debate that the ethanol was the cause of my detonation problems, but until I hear otherwise, I felt that the ethanol was the issue.
Now, I will let others debate that the ethanol was the cause of my detonation problems, but until I hear otherwise, I felt that the ethanol was the issue.
I'll let others debate the black magic angle on how they feel or believe their cars run.
Melting Slicks
Joined: Feb 2004
Posts: 2,111
Likes: 32
From: Damascus MD
I am always ready to learn something new.
What explains the run on when I use 93 octane pump gas that never occurs with the higher octane gas?
Please know that I would really love it if my L46 would run right on 93 octane so I am totally serious.
If you were closer I would also love for us to figure out exactly what is going on.
It costs me an arm and a leg for the 110 octane.
Bill
Last edited by 1974ta; Feb 18, 2013 at 10:30 AM.
Melting Slicks
Joined: May 2006
Posts: 3,438
Likes: 41
From: Raleigh NC
St. Jude Donor '13-'14
I am not sure if Lars rebuilt my carburetor with gaskets that are resistant to ethanol, but I see no reason to chance it and will only put ethanol-free 93 octane into my corvettes from here forward.
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
I had detonation issues after my carb was just rebuilt by Lars and set my timing to 34° all in when I was running 10% 93 octane. I had about a 1/4 of a tank of gas. I went to my local ethanol-free station and filled up with 93 octane and went through about 1/2 a tank that afternoon - by the end of the day no ping.
Now, I will let others debate that the ethanol was the cause of my detonation problems, but until I hear otherwise, I felt that the ethanol was the issue.
Now, I will let others debate that the ethanol was the cause of my detonation problems, but until I hear otherwise, I felt that the ethanol was the issue.
The octane rating of gasoline measures it's resistance to detonation, nothing more. If both gasolines were rated at 93, they were both 93.
I'll let others debate the black magic angle on how they feel or believe their cars run.
I'll let others debate the black magic angle on how they feel or believe their cars run.
In aviation, small piston engines you have a manual mixture control to adjust for altitude, temp, and humidity of the air. The air density essentially. Av gas is 100 octane. You can and will cause a airplane piston engine to detonate if you run that mixture too lean during operation despite the 100 octane rating of the fuel.
Granted, lean mixture is only one of many things that can cause detonation, but it is a sure one.
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
Does your year car have an anti-dieseling solenoid?
Le Mans Master
Joined: Apr 2011
Posts: 6,284
Likes: 1,171
From: Hermosa
Run on, or dieseling as i know it, is usually caused by something getting too hot in the combustion chamber. This could be the ground strap on your plug or carbon build up or some other sharp protrusion. The cause of this thing getting hot is the solution.
Causes could be timing advancing excessively either mechanical, initial or vacuum or a combination of all three. Too high of a heat range plug being used. Too low of octane fuel for the compression/timing. To lean of fuel mixture (main jet sizes too small). Cooling system inadequate. Excessive carbon build up in combustion chamber.
All of these things also cause detonation. So the two are closely related. Fix one and you'll likely fix the other one as well. Hot spots in the combustion can lead to a far more detrimental condition called pre-ignition. In this situation the fuel is ignited by something other that the spark from the plug (just like run-on) during the compressions stroke creating very high stresses on engine internals as the piston compresses the fuel charge while it is burning and expanding.
Causes could be timing advancing excessively either mechanical, initial or vacuum or a combination of all three. Too high of a heat range plug being used. Too low of octane fuel for the compression/timing. To lean of fuel mixture (main jet sizes too small). Cooling system inadequate. Excessive carbon build up in combustion chamber.
All of these things also cause detonation. So the two are closely related. Fix one and you'll likely fix the other one as well. Hot spots in the combustion can lead to a far more detrimental condition called pre-ignition. In this situation the fuel is ignited by something other that the spark from the plug (just like run-on) during the compressions stroke creating very high stresses on engine internals as the piston compresses the fuel charge while it is burning and expanding.
Melting Slicks
Joined: Feb 2004
Posts: 2,111
Likes: 32
From: Damascus MD
Run on
Just curious why it does not diesel with higher octane gas and why it runs soooo much better with higher octane gas.
I guess what I am really asking is based on a optimum set up will an L46 run better with a little higher octane? I have no doubt I can get it to run on 93 pump gas but, trust me when I say it is a completely different experience with the 110 octane racing fuel.
Thanks,
Bill
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Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
IF the ignition is set to optimum curve and advance
and
IF this results in no serious detonation, raising the octane level of the gas cannot yield any additional power.
Once again the octane rating of a fuel only states it's resistance to detonation and nothing else. There's tons of other parameters and measurements possible on a fuel, but they're not directly tied to octane.
I can get mine to detonate at will by using 89 or lower octane but not on 91 or higher. No other facet of operation is affected no matter what octane rating or ethanol blend I use.
If I were you, I'd want to find out why yours runs poorly on 93 and others don't.
and
IF this results in no serious detonation, raising the octane level of the gas cannot yield any additional power.
Once again the octane rating of a fuel only states it's resistance to detonation and nothing else. There's tons of other parameters and measurements possible on a fuel, but they're not directly tied to octane.
I can get mine to detonate at will by using 89 or lower octane but not on 91 or higher. No other facet of operation is affected no matter what octane rating or ethanol blend I use.
If I were you, I'd want to find out why yours runs poorly on 93 and others don't.
Melting Slicks
Joined: Feb 2004
Posts: 2,111
Likes: 32
From: Damascus MD
IF the ignition is set to optimum curve and advance
and
IF this results in no serious detonation, raising the octane level of the gas cannot yield any additional power.
Once again the octane rating of a fuel only states it's resistance to detonation and nothing else. There's tons of other parameters and measurements possible on a fuel, but they're not directly tied to octane.
I can get mine to detonate at will by using 89 or lower octane but not on 91 or higher. No other facet of operation is affected no matter what octane rating or ethanol blend I use.
If I were you, I'd want to find out why yours runs poorly on 93 and others don't.
and
IF this results in no serious detonation, raising the octane level of the gas cannot yield any additional power.
Once again the octane rating of a fuel only states it's resistance to detonation and nothing else. There's tons of other parameters and measurements possible on a fuel, but they're not directly tied to octane.
I can get mine to detonate at will by using 89 or lower octane but not on 91 or higher. No other facet of operation is affected no matter what octane rating or ethanol blend I use.
If I were you, I'd want to find out why yours runs poorly on 93 and others don't.
However, I am not alone in this either. Other guys with original L46 and LT1 for 1970 have reported the same issue.I will recheck everything in the spring. I cannot start it now as the battery is disconnected and I have the underneath disassembled for restoration and detailing.
Bill
Race Director
Joined: Jul 2001
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Team Owner
Joined: Jul 2008
Posts: 23,419
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From: In limbo
St. Jude Donor '13-'15, '17 thru '22
First of all Mike, I feel a need to school you on the operation of aircraft engines like that fella above. Well, maybe not.
Anyway, to pick a nit:
If this results in NO detonation at all, raising the octane will not improve performance. Any detonation or pre-ignition will negatively impact the performance of your engine, serious or not.
Anyway, to pick a nit:
If this results in NO detonation at all, raising the octane will not improve performance. Any detonation or pre-ignition will negatively impact the performance of your engine, serious or not.
Race Director
Joined: Jul 2001
Posts: 15,892
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Intermittent, transient or light detonation has real effect on performance. It's not desirable but not sky-is-falling destructive either