Hi - what are the chances of the 121 diff coping with 200 bhp non turbo 13b set up. I've been told that it's a 24 spline (12A and piston) rather than 28 (RX5). Cheers for any thoughts.

I assume your contemplating the diff for your wagon?

If you are I can advise the original diff WILL cope with that hp.

My 13B powered Luce (1800) Estate was dyno'd at 187KW atw on the original diff. My intention was to replace it when it broke but it survived (without any sign of protest) for the few years I had it.

yep - starting to look around for parts. I wanted to switch to disc rear, and 4.1 ratio as starting point (121).

how did you find the gearing on the original diff with the 13b installed?

Just perfect, I used an RX5 5 speed and made up a one piece driveshaft to suit.
There wasnt many cars on the street that could keep up with it in 1st and 2nd gears. Twin 36IDF webers gave terrific torque and original rear drum brakes seemed to work just fine also.

24 spline centre/axles will just cope but don't thrash it because you will very quickly find the limitations of it. If you weld up the centre expect to break an axle.

28 spline centre/axles will easily cope.

The issue with these diffs is more about finding the right gearing. The smaller 24 spline centres have the better gearing (4.1 and 4.4 available) while the 28 spline centres are limited to 3.36 and 3.9.

I have now seen that you can machine the 28 spline hemisphere to take the smaller crownwheel of the 24 spline centre and package that into either carrier and then run the 28 spline side gears etc for the best combo of strength and gearing.

However its alot of mucking around with a standard diff when the trend toward hilux diffs is well known.

/my 2c

Thanks Aaron. Hilux diff would be have to be shortened to fit which would put the price of the package up. Plus it's non disc. Hear what you're saying about the strength though.