diff ratios

[offroader-rama]

i am putting hilux diffs in my sierra and what diff ratios do most like with 31's for on road, 35's off road standed transfer (at moment) with plenty of power on tap.
i think i should go no larger than 4.3 giving me 2800rpm at a 100ks with the 31's with a crawl ratio of about 60, the crawl ratio is not that impresive, but i think an 1.8ltr in a sierra should have enough guts to make up for it.
i was thinking of going even lower 3.9 or even 3.7 but everyone i talk to thinks it wont work well off road and those ratio's are hard to find espesialy as a pair.
i would like to get right the first time. i have around 150 hp with factory low boost, over 200hp if i pump the boost in it oboviosly no good of road when boosted up but fine with low boost and crawl gears are on the cards as i would like the best of both worlds, on and off road!!

[oldcrusty72]

Depending on how hard you will crawl off road, the 4.3 would be good in that respect. If you do a fair bit of road/highway then the 3.9's will go well with 31's. if your going to put in a set of crawl ratios gears anyhow i'd be looking at the higher ratio, 3.9's. then your highway speeds will be more enjoyable, and still have the low ratios for offroad with your low transfer gears. if you don't go with the crawl gears in the transfer then 4.3 ratio will give you a good compromise for both On and offroad.

With the addition of 35's for offroad, then all that changes, someone else might like to help out in that respect, obviously the bigger the tyres you go the lower the diff ration you want, ie: 4.3 as oposed to the 3.9.

Tim

[offroader-rama]

thats what i am thinking, I was keen as mustard on 3.9 but there hard to find unless i go new, and its a lot of money if i dont like them, also because i'm setting it up to be able to run 35's I compromised and thinking 4.3
also i am going to try an auto in her later on, just building another ca18det with a jatco 4sp auto from a turbo vl commerdore, this would also help with crawling, but it will be manual for a while as its all set up now, I want to get it running with the hilux diffs etc and have some fun with the manual while i build the other ca18det / auto up then I'll swap

[NIK]

For reference I run s1 rockhopper $.8 diffs and 33s. Offroad still abit high but on road 85km/h at 4000rpm (speed by gps as speedo is way out)
Nik

[offroader-rama]

thanks,
thats what i thought 4000rpm at 85ks i'd go bananas i want to be able to cruise with the best of them on the high way around 2500 at 100ks i am just relying on that fact that i have a ca18det to give me enough torque to be able to sit at 2500rpm so im not boosted up at 100ks and still over take if i kneed to.

[lump_a_charcoal]

NIK, what revs would you run with standard trans gears at 100KPH?