Current combo
-stock short block lq4
-317 heads
-ls9 cam
-ls9 valve springs
-dw 78lbs injectors
-procomp intake
-gt45 y2004k 69mm (buyed 12 years ago... looks like the ones that can be buyed today, but the turbine housing is not interchangeable... try both... this make lower back pressure)
-"Denmah special" wastegate and intercooler
-3" cold side
-home modified passenger side manifold (flipped) and driver side ebay header modified 2,5 cross tube
-aem water meth
-92mm ebay t.body
-3500 rpm stall
-th400 unmodified
-stock 8.5 10 bolt rear end 2.56 gear open diferential
-28x10,5 r15
-lots of dyno time , 4 flamed pistons and a plastic intake at the trash
-4250 lbs with me

20180721_153121 by JKK posted Oct 18, 2018 at 9:04 AM

20180728_162322 by JKK posted Oct 18, 2018 at 9:04 AM

20181008_122905 by JKK posted Oct 18, 2018 at 9:04 AM

Tuned on 87 aki treated with Racegas Ultra to 108 oct (87 is the best pump available here) @135kpa (wich equals 6.8psi at this elevation )16 degrees advance

20181008_122018 by JKK posted Oct 18, 2018 at 9:04 AM

Screenshot_20181013-190352_WhatsApp by JKK posted Oct 18, 2018 at 9:04 AM

98a4a80b-4577-4c21-8069-ae1e47047c49 by JKK posted Oct 18, 2018 at 9:04 AM

12,57 at 125,62 mph (note that my slip shows km/h) was my best pass, i crossed the line @ 5800 rpm at 2nd gear, clearly i don´t have enough gearing... but don´t know how to calculate the best option, anyone willing to help?

 

You can use a 1/4 mile gearing calculator To get a ballpark.

 

yes i do... it suggest a 3.87... i found it a little radical....

 

I was unable to get any of your attachments to work. FYI
The easy answer is 3.7x

You went through in 2nd. which for a stock th400 is 1.48 ratio

Your gear ratio is 2.56 So if you want to move up to third gear at the same rpm you'll end up with 2.56x1.48=3.78 final ratio
So all else being equal with a 3.78 gear you would be going through the traps at the same rpm but in high gear. So 5800rpm would be 125MPH still, but in third gear.
As your clicking the traps at 5800 you will have about a thousand rpm to grow as you get faster.
At 7k rpm you would be at 156 with a 3.73

You could also run a 4.10 gear and that technically would be better at your power level as the traps at 125-ish would be 6300 rpm, but as your only at 6-ish PSI I suspect you will eventually turn it up and I do not think you will see a bunch of E.T. difference between the two.
One thing I noticed, was your converter slip was pretty low according to the math at 1.7%

 

I'd simply rev it higher and turn it up. The converter and all will act differently at more RPM and power. Once you have that info, base your gearing off it and your targeted best RPM range. The LS9 will like RPM. Try shifting it at 6800 around 14-15lbs. That's a pretty small charger for a 6.0, it might peter out before that. Keep timing around 10* at first and bump it a degree at a time watching MPH and plugs. It will stop making huge gains at some point and/or the plugs will indicate it's too hot.

Then get your trap VS weight for a power estimate and try to hit the traps around 6800-7000 if you want max effort.

600-650 is about where the GT45 peters out. Going by your weight and trap you're already close to that. Seems liek really good numbers for 7psi @ 4200lbs