Factory DIFF RATIO:s or what do you have

LJ, SJ
toy yoda
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Factory DIFF RATIO:s or what do you have

Unread post by toy yoda » April 15th, 2013, 8:58 pm

Hey All
Something ive never researched till now!! Does any one know thr std factory diff ratio for an 87 sj50 sierra.

i need to make some changes to one i have... i need to know what ratio's i might have ( aside from counting) to do some calculations to drop RPM.

According to the on road figures i have around a 5.3:1 centre. thatss 3000rpm @ 80km/h on 30" tyres.

I dont need to increase power but i need to drop RPM dramatically to make it daily useable... but 3000rpm at 80 isnt realistic

What ratios do you run, what RPM, speed and tyres do ya have.. any info i can use to make desicions wouls be sweet
ideally on paper i want to run 4.1"s .......... 4.1s at 3000rpm on 30"s sits at 100km/h which is exactly what i want.... thats on paper..

Cheers
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toy yoda
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Re: Factory DIFF RATIO:s or what do you have

Unread post by toy yoda » April 19th, 2013, 10:52 pm

Well guess no one out there drives a sierra anymore, oh well!! :rolleyes:
________________________www.loveday4x4adventures.com________________________
thanks to... APM Radiators.. DRW automatics..Boss Racing Diffs..Sprint Auto Parts.. Bob Jane Marion..Noarlunga refrigeration..J&S Suspension (et4wd)..Heinrich Performance Dyno..

whincup
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Re: Factory DIFF RATIO:s or what do you have

Unread post by whincup » April 20th, 2013, 5:55 pm

Narrow track sierra: 3.9 <<should be yours
Wide track sierra: 3.7
1L sierra: 4.1

thats standard diff ratio's... realistically i think 3500RPM @ 100 is roughly where you want it, the engines are just a little gutless for anything less i think. stock gearing/tyres puts it about there anyway. mine doesnt have a tacho so i cant say what mine revs at. you probably already know, but sierra's transfer in high range is roughly a 1.4 reduction stock, a lot of people forget to take that into account in RPM calculations since most 4wds are a 1:1 stock high range ratio

masterA
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Re: Factory DIFF RATIO:s or what do you have

Unread post by masterA » August 30th, 2013, 3:28 pm

^^^ what Wincup said

My Maruit (which was originally 1L) has 4.1 diffs with 31' tyres
I had 4.9 reduction gears...it sat on 3450rpm which was in my opinion perfect
I put a set of 6.5 reduction gears (which is 187% reduction) with the same tyres and diff ratios and it now sits at 3,950rpm

Getting reduction gears to run bigger tyres is a good option
You can get 4.16, 4.9, 5.14 and 6.5 reduction gearing from Low Range Offroad
http://www.lowrangeoffroad.com/
There's a chart on there to tell you different reductions

sgalliani
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Re: Factory DIFF RATIO:s or what do you have

Unread post by sgalliani » November 29th, 2013, 1:09 pm

masterA

I'm sorry, but I can't understand the differences between the 4.9 and 4.16 (yes, you can say the "reduction", but what does it mean?)

I will use my Zook on tons of SAND; MUD; HIGHWAY; AND HILL CLIMBING!

whincup
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Re: Factory DIFF RATIO:s or what do you have

Unread post by whincup » December 2nd, 2013, 8:34 pm

I'll try to explain... when you say 4.9 or 4.16, it should be stated as '4.9:1 ratio'. that means to make the output shaft spin once, you had to spin the input 4.9 times. . means that the input has to spin faster than normal to make the same speed on the output. it "reduces" the output rotation speed relative to the input speed.

to give an idea of real world use, with the old transfer case, 1st gear low range at idle speed might have been about 5km/h, and to do slower i needed to slip the clutch a LOT. the new gears allow me to do almost half that, about 3km/h at idle. means i dont ride the clutch anywhere near as much. these figures might not be 100% accurate but about close to it

for sand and mud, 4.19 will be fine, especially if you only have 29" tyres (i think thats what i read in another post?) i have the same, and in sand i'm finding myself using 2nd and 3rd low where i used to have to use 1st low

sgalliani
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Re: Factory DIFF RATIO:s or what do you have

Unread post by sgalliani » December 4th, 2013, 4:20 am

Did you mean, 4.16, right?

And, do you know if I need some special kit to swap one t-case for the other. Remember that I have the t-case with chains and I will buy the old one, from a 1995 Zook.

whincup
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Re: Factory DIFF RATIO:s or what do you have

Unread post by whincup » December 6th, 2013, 7:26 pm

yeah, i didnt make a lot of sense in my last 2 lines there. i have i have 31's, and with 4.16 for sand and mud thats great. i would have gone the 4.9, but it was going to be about $150 more. but i cant comment on whats needed to swap the transfers over. as far as i know its direct bolt in, all the mounts are the same, and pretty sure the flanges are too, but i've never owned a coily so cant say for sure

sgalliani
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Re: Factory DIFF RATIO:s or what do you have

Unread post by sgalliani » December 10th, 2013, 11:37 pm

So, you mean if I have enough money for the 4.9 will be a better option?

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