high compression engine and ethanol in gas
08-05-2010, 12:51 PM
#1
Pro
Thread Starter
high compression engine and ethanol in gas
Its been a long time since I have posted here, but I have a problem I am trying to figure out and I am guessing others are dealing with it as well.
I own a 1969 with an L-46 high compression 11:1 engine. Up until a few years ago I could still get 94 octane gas, no ethanol. Occasional detonation issues, but solvable with Av gas. For the past several years, the best I can do is 93 with 10% ethanal. I am no mechanic, but I have played with the carb a bit. In fact, I own two, the original quadrajet that was set up by Lars a five or so years ago and another a used Quadrajet that I picked up at NAPA.
Frankly, since ethanol was added my car runs terribly. If I don't cut the gas 4 to 1 with av gas, it backfires and just is no fun to drive. My engine guy and I have switched carbs and I am surprised to say that it seems to run better with the NAPA carb than the original. We have played with timing (this guy used to operate a dyno and is well versed in building and tuning engines) and we can't seem to find a happy medium regarding idling (tends to idle high). When setting the timing it seems to run well but the next day it just seems poopy. We did change out the points for a Petronix ignition and that seemed to help a bit.
So, how are the rest of you guys with old school high compression engines dealing with the gas / ethanol?
Mark
I own a 1969 with an L-46 high compression 11:1 engine. Up until a few years ago I could still get 94 octane gas, no ethanol. Occasional detonation issues, but solvable with Av gas. For the past several years, the best I can do is 93 with 10% ethanal. I am no mechanic, but I have played with the carb a bit. In fact, I own two, the original quadrajet that was set up by Lars a five or so years ago and another a used Quadrajet that I picked up at NAPA.
Frankly, since ethanol was added my car runs terribly. If I don't cut the gas 4 to 1 with av gas, it backfires and just is no fun to drive. My engine guy and I have switched carbs and I am surprised to say that it seems to run better with the NAPA carb than the original. We have played with timing (this guy used to operate a dyno and is well versed in building and tuning engines) and we can't seem to find a happy medium regarding idling (tends to idle high). When setting the timing it seems to run well but the next day it just seems poopy. We did change out the points for a Petronix ignition and that seemed to help a bit.
So, how are the rest of you guys with old school high compression engines dealing with the gas / ethanol?
Mark
08-05-2010, 01:44 PM
#3
Le Mans Master
Member Since: Apr 2001
Location: Was New Orleans but swam to Baton Rouge LA
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You probably need a slight jet or rod change in the carb. With the 10% ethanol it will need to richen up a bit to be on the right mixture. What is the timing set at? You may need to back off a degree or two.
08-05-2010, 04:31 PM
#4
Maybe the ethanol is only at 10%, but then it may be more. I have been adding up to 1 gallon of C12 race fuel to the tank. The engine seems to really like it. At $11 per gallon, it better!
Last edited by Faster Rat; 08-05-2010 at 05:25 PM.
08-05-2010, 05:27 PM
#5
On my 1969 L46, I run Sunoco 93 mixed with Cam II 110 octane leaded racing fuel. Costs $7.00/gallon. Just drive her on weekends when its not humid and sunny. She likes it.
