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techtalk:ref:engctl01 [2023/08/07 19:21] ixl2relax [Sub Documents] |
techtalk:ref:engctl01 [2024/01/13 22:22] hippysmack |
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| ===== Why Adjust The Spark Timing? ===== | ===== Why Adjust The Spark Timing? ===== | ||
| - | Quoting XLForum member, **RacerWill**:((http://xlforum.net/forums/showthread.php?t=1422868 Post#15))\\ | + | Quoting XLForum member, **RacerWill**:((https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-electrical/sportster-motorcycle-electrical-and-ignition/132778-daytona-tc88a-do-your-own-mapping-tips-questions?t=1422868+Post#15))\\ |
| | One of the things that makes understanding timing difficult is that we're talking about 2 different time frames - crankshaft degrees for spark and real time combustion. We light the fire based on crankshaft degrees and engine load but actual burn time is in real time. To get optimal performance we need to light the fire early enough so it has just the right amount of real time to reach max cylinder pressure just after TDC - so it can expand and smoothly push the piston down, this is called MEP or Mean Effective Pressure.\\ \\ Typically, you want max pressure to occur about 7 degrees after TDC. Running too much advance starts the burn too early and max pressure happens at or before TDC, causing "ping" (actually knock). Conversely, not enough advance to the spark causes max pressure to happen too late, producing less power and laboring the engine, making it run hot.\\ \\ The programmable advance maps on the TC88A, and other modern ignition systems, allows timing curves to be altered at any RPM and any load. By trial and error the best map can be found. I didn't know about having all advance in at 3200rpm but that makes sense to me. I run about 32 deg advance but my compression is a little higher than most and compression slows burn time. | | | One of the things that makes understanding timing difficult is that we're talking about 2 different time frames - crankshaft degrees for spark and real time combustion. We light the fire based on crankshaft degrees and engine load but actual burn time is in real time. To get optimal performance we need to light the fire early enough so it has just the right amount of real time to reach max cylinder pressure just after TDC - so it can expand and smoothly push the piston down, this is called MEP or Mean Effective Pressure.\\ \\ Typically, you want max pressure to occur about 7 degrees after TDC. Running too much advance starts the burn too early and max pressure happens at or before TDC, causing "ping" (actually knock). Conversely, not enough advance to the spark causes max pressure to happen too late, producing less power and laboring the engine, making it run hot.\\ \\ The programmable advance maps on the TC88A, and other modern ignition systems, allows timing curves to be altered at any RPM and any load. By trial and error the best map can be found. I didn't know about having all advance in at 3200rpm but that makes sense to me. I run about 32 deg advance but my compression is a little higher than most and compression slows burn time. | | ||
