Taller 5th Gear or Lower Diff Ratio ??? (1 Viewer)

Joined
Mar 9, 2017
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3
Location
NSW Australia
Hi,

I am sure this has been asked before but searching on the forum is not real good (even the advanced search) and it just brings up loads of completely irrelevant stuff.

My son recently went to work os and gave me his precious 80 series. We have decided to do it up and keep it. However one issue is that it revs its head off at 100km/h and after we put a turbo on it I wanted to know if we can slow the engine down a little at highway cruising speed.

1: We have to get the gearbox synchro done so while we have box apart can we get the 5th gear upgraded?

2: Alternatively do we need to get new diff centres with lower ratios. If so what is the likely ratio we have now and what ratio can we/should we change to (it is stock natural 1998 1HZ diesel 80 series but we are going to put a light turbo on it)

thanks for any advice
 
Joined
Mar 9, 2017
Messages
3
Location
NSW Australia
You can get 3.73 and 3.55:1 gears for the diffs.

3.55's would drop your revs 15%

Thanks for that quick reply, I don't particularly want to put taller tyres on it as it is already lifted ~50mm. I was sort of hoping that we could do a 5th gear ratio change as getting two new diffs will be expensive thats if I can get them :-(

Can I ask another idiot question: what diffs are most people using with a lightly turbo'd 80 series: the 3.73 or the 3.55 ?

I guess I start ringing the wreckers for two diff centres .....
 

mudgudgeon

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Dec 17, 2007
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4,559
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Sydney, Australia
there is no alternate 5th gear ratio for the standard HZJ80 gearbox. 5th gear is integral to the cluster gear,not separate like some other boxes.

4.11 is the standard diff ratio. I would not change your final drive ratio by anymore than 10% whether with diff gearing or rubber overdrive. You'll find the 1HZzzzzz very sluggish and lacking torque if you go beyond a change of 10%, and you'll be reaching for 4th gear far more frequently. A turbo will help this a bit
I own a HZJ105, a change of 13% in my final gearing made mine a complete slug to drive.


the 1HZ is happy to rev at highway speeds all day long. If your not used to them, it will sound like its revving it's head off, a swiss watch they are not!
highway rpm around 26-2700rpm is normal


also, if you haven't already found it, lcool.org/forum is a great aussie based landcruiser forum with heaps of solid technical advice available.
it's also a good place to read about the pitfalls of turboing the 1HZ. It's not all beer and skittles if not done right.
 
Joined
Mar 9, 2017
Messages
3
Location
NSW Australia
Hmm, tried to reply and cant delete the above message.

We have decided to put the 3.71 centres in it but will keep the 4.11 in case we ever want to sell it to someone who wants to serious 4WD.

The cost of the two new centres is ~800 and fitting is about 600 so its not too bad if it gives us the desired result.

Thanks to all who replied, assistance appreciated
 

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