Just remember...your low mph can be affected by "slow shifts" or early shifts...can you comment on either?
I would set your timing at 16* and keep your stock FP (39psi) or a couple more lbs than that...and shift it quick and at 6k.
Yeah a slipping clutch can hurt your mph...my last trip to the track was almost 6mph slower (smoke the clutch BAD)...barely see the camaro I was racing in my rear view because the haze
I have been shifting at around 6000-6100 consistently, and I am definitely do not granny shifting by any means. I wish there was a cut and dry way of testing if my clutch was shot, because that is one of the last options I have boiled down to.
I just got my new diff. put in my car today, so that should help greatly getting off the line. I also found out that the gears I had in my car were actually 3.55's and not 3.73's, they were in the car when I bought it and was told they were 3.73's. Anyway, I put 3.73's in when I put the new diff. in, so I am pretty excited now to get to the track with both wheels spinning and 3.73's instead of 3.55's. We'll see how much I improve my 13.3 @ 104.5.
Now that you'll have your posi back and better traction its time to start working more on your tune. The increased traction alone should help your low trap speeds. The 355 to 373 gear swap should be worth a mph (I woulda went 4.10 personally) Make a few passes as is to get used to the car again, then try 2* more timing. When I had that combo I went from 14* to 18* and gained 1.5mph. I tracked tuned it then I went to the dyno and my tune was dead on perfect. I did 304hp/339tq. Just keep playing with things but make ONE change at a time. I went 12.8 @ 107 shifting 400rpm's too early witha small 65mm tb and junk shorty headers. I can only imagine what I coulda did with a bigger tb, longtubes and 6200 rpm shifts Keep us posted!
Yeah killer canary does BAD: with a "small" 65mm TB and bad shorty headers trapping 112.51mph in a 3600lb sn95 vert The throttle body is plenty big enough and the longtubes help you in the mid-range a bit...nothing major to spend money on swapping.
The problem with making changes at the track is there is no way you can recreate your exact shifting speed or exact rpm you shifted at. We are human...so some need to ask yourself was the .1mph gained because of a tune or something else? Better traction, slightly higher or lower shift, quicker shift, tailwind,etc...
A dyno will give you a more consistent tuning log...
Now that you'll have your posi back and better traction its time to start working more on your tune. The increased traction alone should help your low trap speeds. The 355 to 373 gear swap should be worth a mph (I woulda went 4.10 personally) Make a few passes as is to get used to the car again, then try 2* more timing. When I had that combo I went from 14* to 18* and gained 1.5mph. I tracked tuned it then I went to the dyno and my tune was dead on perfect. I did 304hp/339tq. Just keep playing with things but make ONE change at a time. I went 12.8 @ 107 shifting 400rpm's too early witha small 65mm tb and junk shorty headers. I can only imagine what I coulda did with a bigger tb, longtubes and 6200 rpm shifts Keep us posted!
Tuning is exactly what I plan on doing next. I just had to fix the "mechanical" problems first. Actually, I also found out today that my emergency brake was stuck on, because my right rear drum was badly grooved and had no brake pad left. So theoretically I could have had the e-brake slightly applied, but I am not going to use that as an excuse because I doubt it was really on at that point or I would have noticed. I plan on playing with timing and fp at the track as well the next time I go, we'll see what happens.
After all that, a dyno tune will hopefully take place this summer too.