Re: L-79 distributor blueprint overhaul
I have always said that racing engines are completely different animals than road engines. That does not mean that a spark advance map for a given engine would be different for road and race use. The objective is to achieve the most aggressive detonation-free spark advance possible for the full normal operating range of the engine. Road engines have to operate from off idle to max revs. With racing engines the only real concern is the top third of the rev band.
Jim's setup is probably 98-99 percent optimized, and it doesn't detonate despite my efforts to make it do so by loading it up at low revs climbing a steep hill, so it's not going to blow up or wear out prematurely. The parts cost about 20 bucks and can be swapped in without removing the disitributor - maybe an hour or so to do the job including setting the timing.
Will your L-79 detonate? How do you expect me to know for sure. What's the actual, true compression ratio of each cylinder? Does it have the OE .018" gasket, or something thicker? Jim's engine did not detonate with a .036" gasket, but we don't know if it has the OE domed pistons, or something else that would lower the CR. In most cases assuming the engine is in its original configuration with no more that typical Flint-built true CR, which is several tens less than advertised, there will likely not be significant detonation. There are also cases where an aggressive spark advance map worked detonation-free even when operating on unleaded regular because the domed pistons were replaced with flattops and a thick head gasket, which dropped the CR about two full points.
In my San Diego presentation that you can download off the Web, I gave starting point suggestions for the various OE engine families based on my knowledge of the physics and chemistry going on inside these engines and 50 years of experimentation. I also clearly stated that each individual engine must be tested due to differences in driving conditions and internal configuration such as compression ratio. I'm neither clairvoyant nor a magician. I don't know the CR of every cylinder of every engine out there, and most owners only have a vague idea or aren't even close, nor do I know the typical temperature and air density every time an owner takes his car out. These are known unknowns that effect detonation and must be determined by testing by each owner for each car!
If the recommended setup results in significant detonation, I recommended two ways that can be used individually or jointly to quell it.
Now, if you ask the same question a third time, the answer is the same, and the reasons why most OE spark advance maps aren't fully optimized as-built is in my San Diego presentation.
I recommend you download and read it as it will also answer questions that you haven't even thought of, yet. I did to to help guys understand what's going on inside an engine and how to improve both performance and fuel economy with changes to the spark and fuel maps that are very inexpensive and don't take a lot of time, not to sit lonely and unused on a Web server.
I can lead you guys to the water, but it's up to you to take a drink.
Duke
I have always said that racing engines are completely different animals than road engines. That does not mean that a spark advance map for a given engine would be different for road and race use. The objective is to achieve the most aggressive detonation-free spark advance possible for the full normal operating range of the engine. Road engines have to operate from off idle to max revs. With racing engines the only real concern is the top third of the rev band.
Jim's setup is probably 98-99 percent optimized, and it doesn't detonate despite my efforts to make it do so by loading it up at low revs climbing a steep hill, so it's not going to blow up or wear out prematurely. The parts cost about 20 bucks and can be swapped in without removing the disitributor - maybe an hour or so to do the job including setting the timing.
Will your L-79 detonate? How do you expect me to know for sure. What's the actual, true compression ratio of each cylinder? Does it have the OE .018" gasket, or something thicker? Jim's engine did not detonate with a .036" gasket, but we don't know if it has the OE domed pistons, or something else that would lower the CR. In most cases assuming the engine is in its original configuration with no more that typical Flint-built true CR, which is several tens less than advertised, there will likely not be significant detonation. There are also cases where an aggressive spark advance map worked detonation-free even when operating on unleaded regular because the domed pistons were replaced with flattops and a thick head gasket, which dropped the CR about two full points.
In my San Diego presentation that you can download off the Web, I gave starting point suggestions for the various OE engine families based on my knowledge of the physics and chemistry going on inside these engines and 50 years of experimentation. I also clearly stated that each individual engine must be tested due to differences in driving conditions and internal configuration such as compression ratio. I'm neither clairvoyant nor a magician. I don't know the CR of every cylinder of every engine out there, and most owners only have a vague idea or aren't even close, nor do I know the typical temperature and air density every time an owner takes his car out. These are known unknowns that effect detonation and must be determined by testing by each owner for each car!
If the recommended setup results in significant detonation, I recommended two ways that can be used individually or jointly to quell it.
Now, if you ask the same question a third time, the answer is the same, and the reasons why most OE spark advance maps aren't fully optimized as-built is in my San Diego presentation.
I recommend you download and read it as it will also answer questions that you haven't even thought of, yet. I did to to help guys understand what's going on inside an engine and how to improve both performance and fuel economy with changes to the spark and fuel maps that are very inexpensive and don't take a lot of time, not to sit lonely and unused on a Web server.
I can lead you guys to the water, but it's up to you to take a drink.
Duke
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