1KZ conv. diff ratios

[U-BOAT]

i'm usure what diff ratio's to use in my 1KZ conversion into my LN65 hilux. i know that my truck runs 4.556 gearing and factory the surf donor had 4.1's. thats not really the problem what i'm faced with is that i'm using the stock A340F automatic gearbox and compared to a hilux manual G52 i don't have a first gear as such. the first in the auto is 2.8:1 (slightly higher than G52 2nd) where the first in a G52 is 3.93:1. so what im worried about is whether my truck is going to be able to crawl along when needed without me having to ride my brakes all the time on steep descents etc. should i go to 4.88 or even 5.29?

[Leithfield]

What size tyres will you be running?

[U-BOAT]

i've got a set of new 33 mongrels to wear out first but after that 35's or bigger. what type of box is in your surf leithfield? i just do't want to find out that it is too high geared and then have to do the diffs all over again.

[Leithfield]

I'm on 37's, with 5.29's & a late-model R150F manual gearbox; this has proven an excellent combo both on & off road.

Your autobox will allow you to crawl along; however, you will experience a noticeable decrease in engine braking ability on steep decents . The calculations below will illustrate why ...

Here is how to calculate your overall crawl ratio.
Multiply your first gear, times your low range transfer case gear, times your differential gear. For example per your G52 setup you have:
3.93 first gear in your transmission
2.28 low range gear in your transfer case
4.55 gears in your differentials
Your crawl ratio is 3.93 X 2.28 X 4.55 = 40:77 (rounded)

- With A340F:
2.28 x 2.28 x 4.55 = 23.65 (or 42% higher geared than G52)

- With A340F & 4.88:
2.28 x 2.28 x 4.88 = 25.37 (rounded; or 37.8% higher geared than G52)

- With A340F & 5.29:
2.28 x 2.28 x 5.29 = 25.37 (rounded; or 32.55% higher geared than G52)

Changing from 33" to 35" tyres effectively increases your diff ratio to 5.175 & 5.610 respectively; i,e
With A340F, 4.8 & 35's = 34% higher geared than G52
With A340F, 5.29 & 35's = 28.47% (rounded) higher geared than G52.


Hence, short of lower ratio transfercase gears, or dual-transfercase, I would recommend 5.29's if you are intent on progressing to 35" + tyres .

[krawlr]

id run 4.8s which will give you mega lowrange espicially with the lower geared manual box i think 5.29 will be too low and also harder to find for sapares a a good price

my mate has 4.8s for sale i $500.00(x2)so let us know and they will be in wgtn ,and can do a 4.8 lsd for 400.00

[Leithfield]

i'm using the stock A340F automatic gearbox

Agreed Krawlr, but he's using the autobox. Perhaps we can convince him to stay away from the dark side .

[krawlr]

ha yes true

well i ran an auto with 4.8s and no need for lower gearing it did wonders to down hills ,no matter how steep i never seemed to touch the pics and yes same engine too so go the 4.8s brother....

and yes still love the 5 stick not as idiot proof but lock it in and go no chocking or flat spotting

[U-BOAT]

darkside?? the main reason i stuck with the auto is thats what the donor truck came with and why muck with something thats not broke. yeah thanks for the help krawler and leithfield i wanted to check with people who have been there and done that so to speak before i went any further. good effort on the ratio calculation i tried doing it myself but wasnt sure what i was looking at was right. i've worked out that on road gearing is still going to be higher than a G52 setup;

box final diff overall

a340f 0.7 x 5.29 = 3.7
g52 0.84 x 4.55 = 3.87

so i think 5.29's will be the go once i've built my wide diff conversion.

cheers marc

[turoa]

umm, am I not doing something right. Apparently my crawl ratio = 19.43(1st gear)x2.888(low range)x4.88(diff ratio) = 273.8355:1 according to my new gearing.

[krawlr]

you dudes spend to much time on the net my ratio caculator works atreat.........unbolt,refit ,rebolt and well see how she goes,shit too low out she comes next idea boys........

yes i hate numbers