Quote:
|
Originally Posted by J-Ri
1. I'm a mechanic, and I attended a technical fuel seminar some months ago. The teacher said that the spark timing has to be advanced by 40 degrees to compensate for the higher octane. The unit on the web site does nothing other than hold the fuel injectors open longer. Would the computer adjust the timing that far? On the site they say the unit ALWAYS increases the duty cycle of the injector, but when running on gasoline the vehicle computer decreases it so much that the increse puts it where it should be. Wouldn't the stock computer increse it enough for the ethanol if that's true?
|
40 degrees is way off. For the most part, ignition timing doesn't need to change much, but it depends on many factors. Ethanol's flame front speed is the key. Ethanol requires about 30% more fuel than gasoline. Simply increasing the duty cycle of the injectors is fine... IF there is 30% left in it. The problem is that injectors have to stay open longer at higher RPMs where fuel is needed most, BUT as RPMs increase, there is less time for the injector to deliver the needed fuel. Most fuel systems operate the injectors at no more than 80% duty cycle. Adding 30% isn't feasible. The injectors would be remaining open 100% of the time and still not delivering enough fuel.
A stock computer won't compensate properly for ethanol. The problem is tha ethanol's stoichiometric ratio is about 12:1, while gasoline is 14.7:1. If you simply burn ethanol by increasing the fuel ratio, the computer will try to return the mix to 14.7 thereby defeating the purpose. You have to tell the computer (or fool it) into compensating for the right mixture.
Quote:
|
2. I was looking for alcohol carburetors for my truck, and they are about 4x more than gasoline. Is this because of a limited market, or are parts that tolerate ethanol that much more? (The company that sells the conversion says something about DPFE linings for a 10% mix can tolerate 100% ethanol) Would E-85 (or 100) destroy the fuel pump, lines, hoses and injectors? I know even a 10% ethanol mix "damages" some GM injectors (which actually is a defect in the coating on the coil)
|
You need to do a comprehensive change to the fuel system for E85. Anything rubber has to go as ethanol will eat it. Alcohol carbs are expensive because of demand and limited market. The only real difference between a gas carb and an E85 carb are the jets and some of the fuel passages get drilled larger. Nothing special.
Quote:
|
I also have a question about converting a carbureted V8 to ethanol. As I stated before, it is my understanding that the timing has to be advanced by about 40 degrees to run on ethanol. Would it be possible for me to adjust the mixture screw for ethanol, and rotate the spark plug wires by one tower (for a 45 degree spark advance)?
|
Carbs have three circuits. The mixture screws only affect the idle circuit which would only be effective at zero throttle. You would have to alter the jets on the primary and secondary circuits. Most likely you won't be able to find jets large enough and drilling/modifying will be necessary.
Moving the plug wires one post will effect 90 degrees of advance, not 45. Its 45 degrees at the distributor which is 90 degress at the crank. You're better off turning the distributor... but like was said... 40 degrees is way off. Your teacher should be slapped.
Recoil
Tontie
