Octane
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Instructor
Joined: Apr 2021
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Octane
So the guy I bought my 73 from thought jt was a good idea to have 12:1 compression do I need to run 93 and octane booster? If so any suggestions
Last edited by 1973bluevettee; Sep 9, 2021 at 09:19 PM.
Team Owner
Joined: Jul 2004
Posts: 40,338
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From: Redondo Beach, California
Pretty sure you will. Your engine should tell you if you have an octane problem. You'll hear the pinging. I had an engine with 11.5:1 compression. On 91 pump gas,the pinging would sound like the anvil chorus. I haven't used octane booster for a long time. As I recall, there were few brands that actually worked, the rest were useless. How did the seller handle the octane problem?
You can guy high octane racing gasoline in 5 gallon cans. 5 gallons in the tank with 15 gallons of pump gas will probably work. I think the last racing gas I bought was about $70 for 5 gallons. In the late 70's, I bought av gas at the local municipal airport in Jerry cans. Once I became a familiar customer, they would just pump the av gas right into my car. Highly illegal. I'm sure they wouldn't to this today.
You can guy high octane racing gasoline in 5 gallon cans. 5 gallons in the tank with 15 gallons of pump gas will probably work. I think the last racing gas I bought was about $70 for 5 gallons. In the late 70's, I bought av gas at the local municipal airport in Jerry cans. Once I became a familiar customer, they would just pump the av gas right into my car. Highly illegal. I'm sure they wouldn't to this today.
Le Mans Master
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From: LONG ISLAND
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I would ............. unless you the like the sound of marbles in a jar, farts, back fire pops, diesel run on & extra pinging
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Instructor
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Racer
Joined: Jun 2018
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From: NH
Due to security most airports are locked down. But small ones (tiny ones...air strips) usually aren't and will be self serve. Or you can talk to someone at the airport to ask for help. Also, look up fuel dealers that specialize in race fuels (like VP Racing) because they will sell drums of various fuels. I've bought nitromethane and methanol by the 5 gallon drum from dealers and speed shops (neither are at an airport).
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Team Owner
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From: Crossville TN
For the 'long haul' with your new car, you might want to consider going to some nice aluminum heads that will drop compression to 11:1. Then the engine will be 'happy with available 93 octane fuel and you won't have to go to extremes finding needed AV fuels. The car will also be more desirable to future buyers.
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Instructor
Joined: Apr 2021
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For the 'long haul' with your new car, you might want to consider going to some nice aluminum heads that will drop compression to 11:1. Then the engine will be 'happy with available 93 octane fuel and you won't have to go to extremes finding needed AV fuels. The car will also be more desirable to future buyers.
Le Mans Master
Joined: Apr 2011
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From: Hermosa
Drive it an elevation above 5000 ft and you won't have any problem with 93. Problem is they don't sell that octane at those altitudes at the pump.
How much trouble you have will depend a lot on the tune, how well the rebuild was done particularly quench and does it have flat top pistons or domes. How well it's kept cool. Where you get the intake air from, fresh air or underhood air. Without knowing these things it's gonna be trial and error.
How much trouble you have will depend a lot on the tune, how well the rebuild was done particularly quench and does it have flat top pistons or domes. How well it's kept cool. Where you get the intake air from, fresh air or underhood air. Without knowing these things it's gonna be trial and error.
Instructor
Joined: Jan 2021
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From: Lagrange Ohio
7T1Vette has the right idea. Try aluminum heads. I too was stupid enough to build a 440 6-pack for my Challenger with 12.5 to 1 compression.
Tried EVERYTHING as far as octane boosters No luck. Has to have 110 octane racing fuel. Only thing that works for mine. Needless to say at 8 bucks a gallon she doesn't get out much any more.When I pull it to do a color change I'm going to put some sensible pistons back in it. That'll solve the problem.
Good luck.
Tried EVERYTHING as far as octane boosters No luck. Has to have 110 octane racing fuel. Only thing that works for mine. Needless to say at 8 bucks a gallon she doesn't get out much any more.When I pull it to do a color change I'm going to put some sensible pistons back in it. That'll solve the problem.
Good luck.
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Melting Slicks
Joined: Feb 2017
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From: PHX AZ
Avgas at 100 octane is available. In addition to the link below. Many of our larger lakes and the adjacent towns have high octane gas available for JET BOATS.
Stock up on 5 gallon Jerry cans.
https://cutteraviation.com/fbo-servi...t-fuel-prices/
Have you done any timing mapping? (IE knocking the timing back severely to see if you get detonation?)
Unkahal
Stock up on 5 gallon Jerry cans.
https://cutteraviation.com/fbo-servi...t-fuel-prices/
Have you done any timing mapping? (IE knocking the timing back severely to see if you get detonation?)
Unkahal
Safety Car
Joined: Nov 2005
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From: Arizona - If you don’t know CFI, STOP proliferating the myths around it...
You basically have two choices...reduce the CR or use race gas. I wouldn't use AV gas. They sell 100 octane race gas here in AZ at the pump at some stations ( one is next to the track, Love's) and I throw a couple gallons in mine when at the track just to be safe when I play with the timing. 12:1 is pretty high for a street motor IMO. Are you just cruising or racing it? There are various ways to decrease the CR, the choice is yours.
Drifting
Joined: Nov 2007
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From: New York
How do you determine the compression ratio by doing a compression test?
Anyway, I used to have a 11 to 1 stock motor. After two cleaning cuts on the heads and advancing the timing a bit I had issues. When I took the engine apart, there were chips around the rings from the detonation (or pre-detonation).
The next motor had 10.5 to 1. Aviation gas of sufficient octane may work. At 12 to 1, 93 octane may not cut it and you can do real damage to the engine.
Anyway, I used to have a 11 to 1 stock motor. After two cleaning cuts on the heads and advancing the timing a bit I had issues. When I took the engine apart, there were chips around the rings from the detonation (or pre-detonation).
The next motor had 10.5 to 1. Aviation gas of sufficient octane may work. At 12 to 1, 93 octane may not cut it and you can do real damage to the engine.
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Instructor
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-yeah your right my fault my friend told me the wrong info I guess I don’t know my ratio he thought you could covert the psi to ratio but I did reaserch and that’s just not true