Welcome to the forum!
I do not have experience with the Sniper. I do have experience with the same engine you're using. I spent a bunch of time trying to set up a TBI engine using the original 7747 ecm. Ultimately the customer wanted a better performance than I could give with the 7747 so I installed a marine PFI intake and a 7730 ecm.
I read through the GMT400 thread. The two timing tables posted are very rough. The first table has extremely dramatic changes. The second table calls for crazy amounts of spark advance.
With the original ecm, spark advance is kind of complex. There's at least one base table, and then there are special cases like cold engine and wide open throttle (WOT). I can see the base table you've posted for the Sniper on GMT400. Are there any special case spark tables in the Sniper?
Here is a main spark advance taqble I used with a 350/350 TPI engine.
Code:
20 30 40 50 60 70 75 80 85 90 95 100 RPM
400 20.39 22.85 23.91 26.02 23.91 20.04 17.93 14.06 10.9 7.03 4.92 3.16
600 22.15 23.91 29.88 25.31 24.96 21.45 17.93 16.17 13.01 9.84 8.09 5.98
800 24.96 30.94 33.05 28.83 26.02 22.15 18.98 16.17 14.06 10.9 9.14 8.79
1000 29.18 37.97 35.86 33.05 28.83 22.85 20.04 16.17 14.06 10.9 10.9 10.9
1200 32.7 40.08 37.27 34.1 31.64 23.91 20.74 16.88 15.12 13.36 13.36 13.36
1400 34.45 40.08 38.67 34.45 32.34 26.37 24.26 21.8 19.69 16.17 15.82 15.82
1600 35.16 40.43 38.67 36.56 32.7 28.48 24.61 21.8 19.69 17.23 17.23 17.23
1800 35.16 39.02 40.08 37.27 34.1 30.94 26.72 23.91 22.15 20.39 21.09 21.09
2000 35.16 39.02 39.38 37.62 35.86 32.34 28.83 24.61 22.5 21.8 22.5 22.15
2200 35.16 39.02 39.38 37.62 36.21 34.1 30.94 26.72 26.02 25.31 26.02 26.37
2400 35.16 39.02 40.08 39.38 36.56 34.45 32.34 31.29 30.23 29.53 30.23 30.59
2800 35.16 39.02 40.08 39.38 36.56 34.45 33.75 33.05 34.45 33.75 32.7 32.34
3200 33.75 39.73 40.78 39.38 38.67 35.16 35.16 35.16 34.8 34.45 33.4 32.34
3600 31.64 40.08 43.24 41.84 41.13 37.97 36.91 36.91 36.91 35.16 35.16 33.05
4000 31.64 41.13 43.24 41.84 41.13 39.02 37.97 37.97 36.91 35.16 35.16 33.05
4400 31.64 41.13 43.24 41.84 41.13 39.02 37.97 37.97 36.91 35.16 35.16 33.05
4800 31.64 41.13 43.95 41.84 41.13 39.02 37.97 37.97 36.91 35.16 35.16 33.05
MAP
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