Gear Ratio Help

[butcherboyjc]

What would be the best set up for a daily driven truck. I have a 74 620 (automatic version) with a 4.625:1 rear end and the ka24de engine and 5spd tranny in my truck, the 240sx has a stock 4.08:1. The options Im considering are from a 79 620 which has a 4.11 which is close to a stock 240sx, or a 720 with a 3.889. I read this thread http://forum.ratsun.net/showthread.php?t=13600&highlight=720+gear+ratio which was helpful. I read on some 240sx forums that some guys/gals swap to 4.6 or to 3.8 and they both swear that it was an improvement over stock. Any input appreciated.

[kezark31]

well i have the 4spd in my 521 with the stock 4.37 i swapped in 3.88 i only gained 5 mph at 2500. so it really comes down to if you want more grunt off the line or higher top speed. more city driving more highway. check out this calculator

 

http://golenengineservice.com/calc/calcrpm.htm

[DISLEXICDIME]

i say 390's if it is a daily your not going to loose much of the line with a ka in there

[Bleach]

Your truck weighs 600 pounds less (maybe more) than the 240SX.

4.11 should be good but harder to find. 4.375 should also be a good choice. Don't run an undersize tire on the back.

[Farmer Joe]

myself, personally, would go for a 3.70 or maybe even a 3.54 (yes, theyre out there).

 

with a KA itll have plenty of torque to get a little 620 goin.

Edited November 20, 2009 by Farmer Joe

[butcherboyjc]

As for tire size, the diameter shouldnt be smaller than the stock diameter of the 240 or the 620?

[butcherboyjc]

Found a good article that helped me understand a bit more how the gears work. Its good reading material for anyone wanting to know more on gearing.

http://www.carcraft.com/techarticles/how_gear_works/index.html