I am trying to figure out the best ratios on my Nash 5 speed I just picked up.
I don't know what it was used for but its got some funky ratios for 2nd and 3rd.I have some spare gears that came with it and Liberty has
new gears at reasonable prices if I need any.
Is there an online calculator that you can plug in basic specs to calculate optimum ratios? RPM drop?

Street only, Street and Strip or Drag Race only?
What rear gear ratio and tire size?

Drag Race only

I'd stick with the "classic" gear splits unless the car is really weird. Transmission engineers have roughly 100 years of experience at getting a heavy vehicle out of the hole and up to speed.

I will stick to classic progressively less drop splits to allow a centrifugal assist clutch to slip most on the 1/2 shift and progressively less as I go through the gears
Car is not heavy 2500 with me so I don't think I need anything 3.00 or steeper for first. I have enough spares to go 2.71 -3.12 for 1st gear by just buying cluster gears which are $120.I also have spare rear gear sets so I could gear the trans steeper and change rear gear if needed.
The only thing really weird is the current ratios and the owner.

Stick shift starting line ratio can be fun to figure out what works best for your race car
Are you 1/8 mile or 1/4 mile racing?
Where are you shifting it at? What motor combination, B,RB,SB or?
How big, width and diameter are the rear tires.
I use to help a friend drag race a 1970 340 Duster 4 speed car, 12x30x15 inch slicks,5.57 rear gear ratio, 3.09 first gear with stock early A body NP 833 tranny gears
It would dead hook in a mud puddle in a rain storm ,You were really busy the first 300 ft.in that car, it would cross the finish line around 7000 RPM in the 1/4 mile, no 1/8 mile racing back then
IHTHs

A call to a race manual trans manufacturer may shed some light on your needs, along with the folks that make your clutch, and the chassis builder of the car, if it was a well known builder. I personally have theorys, but they aren't worth much without experiance and results. My guess is once you get deep enough for low gear, your ability to speed shift will be a determining factor on further improvements in ET and consistancy.

I used this Tremec calculator and found it to be spot-on.

https://www.tremec.com/calculadora.php

Cab-
1/4 mile 95%
Combo is basic Gen3 5.7 Hemi n/a 550HP. I just upgraded to single plane intake. Last pass 9.82
Shift at 7k now.

Greg-

I have talked to Liberty and they suggested ratios based what other people chose with similar times. 3.25 first.
Also talked with Cale @ Black Magic Clutches about a slipper style clutch.
I guess I need to call them back.

From research I've done, what I'm reading is yes you have to be cognizant of your motors range but the real focus is working within your clutch tune?
I am trying to do this conversion within a reasonable budget.
I did find an online gear ratio tool. One thing it will not show, straight gear calculations do not account for any clutch slip.

My Richmond has the 3.27 low gear and I was racing it for a while with 4.56 gears in the rear. I was pulling second just past the tree. The 4.10s worked out a little better and I had a little more time to hit the gear change. I really like the 5-speed because it keeps the engine in the happy range with very little RPM drop at the gear change especially with the faceplate gears and the V-gate shifter.
Gus