Outer Limits 4x4 Board

i picked up a set of rugger diffs the other day and have decided to throw them under my fez,
i will be using rear fez springs up front as well.

what are the important things to look out for?

What ratio ?

If they are lower that stock (5.285:1) and you have/put larger tyres on then you are going to end up with a major problem.

THe Feroza transfer reduction is just not low enough..

not to sure what ratio they are just picked them up off a guy on trademe.co.nz and all he could tell me was that they were out of a rugger, 2.8td model.

They will most probably be 3.36363636

Waaaaay to low for a standard Roza tcase.

is that a bad thing as im gona be running 31's or bigger

Being blunt - they will be a disaster !

Highway revs will be waaaay to low IMO, 5th will be unuseable.

Feroza's low range is around 1.7 which is too high as stock let alone the wrong diffs and tyres. Feroza's also don't have excess power or torque so it all gets worse not better

I know there's lots of people on outers who are negative, but IMO this is a really bad idea. Spend some time with a gearing calculator ( lots on the internet ) and it will give you some idea of the magnitude of the problem. Around 3500 RPM @100k in 5th wouldn't be bad for a stockish engine.

As for low range crawl, a good place to start is 60:1+ on 31's, my guess is you would be lucky to get 25:1.... I am running around 160:1 includung the torque converer.

Some deep though now will save you lots of work, money and eventual misery.

can you please explain this to me im not up with all the ratios etc. i'll also wont be running under 31's once i do the conversion. it will then be followd by a engine/drive chain upgrade. and im willing to loose top end speed if im correct in my thinking for the ability to go more places

2roky wrote:can you please explain this to me im not up with all the ratios etc. i'll also wont be running under 31's once i do the conversion. it will then be followd by a engine/drive chain upgrade. and im willing to loose top end speed if im correct in my thinking for the ability to go more places

you will be adding a shitload of topend speed, and the gearing will be way to high offroad.

3.36 works well with 31s and v6 commodore motor.

Crawl ratio = diff ratio x low range ratio x 1st gear ratio

If its an auto then you can multiple by the converter stall ratio as well, but some will not agree so thats up to you - or irrelevant.

As for road speed.... if for example you half the diff ratio you car will do twice the speed as it did before at the same engine rpm.
In practice what it really means is that at 100k for example the engine will be doing half the rpm and thats impractical as the engine needs rpm to develop enough power to push you along.

So you need to know the transmission gear ratios, the diff ratio and the tyre diameter to calculate if the engine will be operating at a useable rpm at your targeted driving speed.

Same thing applies for a transplant, no matter how good the engine is if its wrongly geared it performance will be unsatisfactory.

Try talking to a few transmission rebuilders if you cant do the calcs yourself. You can download Feroza manuals from warfs.org which will give you the Feroza specs.

Randomly fitting mechanical components without a significant amount of understanding of how they all interact is VERY unlikely to work out.

Still you seem to have lots of energy and if you couple that with a sound design you could end up with a great toy.

that makes sense to me now. i was thinking that it was the other way around. that the lower diff ratio would slow things down not speed them up lol.

HotFourOk wrote:They will most probably be 3.36363636

Waaaaay to low for a standard Roza tcase.

Way to high you mean

r0ck_m0nkey wrote:

HotFourOk wrote:They will most probably be 3.36363636

Waaaaay to low for a standard Roza tcase.

Way to high you mean

Yeah.. the ratio is high, but the number is too low I was trying not to confuse him more!

And I was conforming to MM's precedence of 'lower' as in the first reply.

Yep the old two card shuffle...

A high numerical diff ratio gives a low speed.

Thats' one of the reasons I like Toyota centres, firstly because them make a 5.285:1 to match the Feroza and also because there are higher ratio's still available 5.71:1 which will be great for 33's

looks like im gona have to save up for a set of hilux diffs then