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Discussion and questions related to the course EFI Tuning Fundamentals
So I just want to start off and say I do apologize for all the questions I've created on posts lately.. but I am starting to understand some things that I would never have thought to have before like closed and open loop, and why the ecu runs on closed loop, for fuel economy reasons/ emissions. I've learned how to set my stoich air fuel ratios and learned what stoich lambda and air fuel ratio actually means and what its value is for e85 and regular pump gas. So, I've watched this lesson about three times now and before I couldn't understand at all how ignition timing works whats so ever.. but I went and used my favorite research source which is google.. and read some things on ignition timing and now I know that ignition timing happens on the compression stroke and where ever it is set on the ignition table like 16 degree before top dead center the combustion and air fuel mixture happens 16 degrees before top dead center.. I hope this is correct.. so my question is, how do I know when to take timing out of my ignition tables when I'm looking at my maps for it? If the ignition timing is happening 16 degrees before top dead center, it would mean that its running more on the rich side? And if the ignition timing happens after tdc it would mean that its on the leaner side?? And if the ignition timing happens on the compression strike before it reaches top dead center.. it would have more of a power loss than gain? Since the piston is traveling up while the combustion mixture is happening and causing a restriction on the compression stroke? If it happens a bit after it would gain power? Moving the piston down faster and transferring the power to the crankshaft at a faster rate? Sorry for throwing all these questions in all together again.. but to sum it all up.. my main question is.., how do I find out where I should set my ignition timing? Start by taking away, then adding a degree to the whole map to see if it runs better or has a gain? But this would only work on a dyno correct?
What we are doing with ignition timing is controlling where the peak cylinder pressure occurs. What we want is for this to happen around 10~16 degrees ATDC. Having it happen here provides the most effective transfer of the cylinder pressure into the crankshaft through the connecting rod and piston thus maximising the amount of torque generated. Where the timing point is for this to occur depends on the engine and the load that is on the engine.
To have this peak pressure occur at this point, we need to have as close to complete combustion occurring by this point, this is done by moving the Ignition Timing to suit, what we are looking for is the minimum timing required to provide the best torque (or the knock limit of the engine if it is knock limited). As the speed of combustion is relatively fixed, the ignition timing needs to be advanced as the engine speed increases to provide enough time for the combustion to occur and peak pressure to arrive within that window. The optimum point for this to occur is typically in the BTDC region of the compression stroke.