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Scott:
I would be hard-pressed to improve on your excellent summary of the issues at hand. Nicely done.
I cannot honestly give more details for two reasons, 1) I don't know them all, and 2) This was an R&D run on a NA TCM engine set up like TCM wants it set up with only the one difference of advancing the timing 2 degrees. The resultant ICPs were 1130-1140psi and it was not at max power or at max ICP mixture! It could easily have been made worse--and it wasn't even TC'd.
My point, Scott, is that we see folks diddling with timing changes who have no hard ICP data--only what they *think* will be the result or some *calculation* and we now know, from hard data, that that decision tree in this instance could be flawed--with nasty results. Some of the guys who who have seen this data and were common choice builders of engines for the exp. market will no longer build/warrant an engine on which the owner plans to use EI. I find that telling.
My current position on EIs is that the jury is still out on what's being done by some folks who are doing so without hard ICP data--and as far as I can tell, that's most of them.
Walter
Walter, Would you care to give us more complete information? For any given combustion event in a piston 4-cycle engine with certain compression ratio, A/F ratio, fuel octane, # of ignition points,valve count, piston head and chamber shape there is an optimal timing to deliver appropriate pressure during the power stroke. If the timing is changed, the pressure delivery range is changed. Some of the ways to change the timing of the combustion events would be to change the A/F (lean or rich), the octane, and uncommanded ignition events (pre ignition, detonation). If the event is late, the best pressure applied to piston power stroke may be less effective because there is little work for the piston to do. If the event is too early, the pressure may work against the purpose of the engine - the piston may still be on the compression stroke or too early in the power stroke where the rod angle isn't in a position to smoothly deliver the power to the crankshaft, both causing more stress on the engine than is desirable. The fixed timing compromise delivers less than optimal power under conditions outside the engine design range specified by the designer. One of the negative ways to change the timing of the combustion event is to diddle with the mixture so that the engine is operating 20-30F ROP under high power - this can place abnormally high pressure on the piston/chamber and at the wrong time. When all the engine parameters are appropriately controlled, including ignition timing and A/F ratio, the engine can smoothly and efficiently deliver the power within its design and engineering. Thanks for keeping us within the bounds of reason. Scott Krueger Green efficiency thru the use of appropriate timing. If I could only get my stock market timing right........................... . I think what is happening is that the thetaPP is changed less by the loss of the mag than by the loss of the EI. This had little to do with the amount of fuel being burned.
BTW, I just looked at the thetaPP data on a set-up where the timing was changed by as little as 2 degrees, advanced. The thetaPP was advanced to 10dATDC and the peak pressures were above 1100 psi. This is not a good thing. You guys do as you please, but that's not something I want to do to my engine. Spark plugs begin to be blasted out of cylinders at 1200psi--by imperical experience.
These are observations of hard data. |