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The diff in my NC race car has a stuffed crown & pinion.
I have a spare 4.1 set, but would like to go shorter.
Does anyone know a source, preferably in Australia, for 4.3 to 4.5 crown and pinion sets for an NC diff please?
Will a RX-8 C&P fit?

No oem options. Not 100% certain if the RX8 internals fit but I don’t think it does. You could see if companies like Quaife do gear sets that fit the NC Carrier.

Thanks "Custardtart".
Finding a replacement short gear set has proven to be difficult.
So I have decided to build the diff as a 4.1, and then use the existing C&P gears to provide measurements to help find a replacement.
I will post the outcomes here.

RX8 internals will not work at they are an 8 inch diff as opposed to the NC being 7 inch.

Apparently you can fit an entire RX8 housing in if you also get the power plant frame and modify it to fit. So custom fabrication work.
Or modify the NC frame, also fabrication work.
Then the shafts are different and you need the RX-8 knuckles and hubs as well.

See this. Best resource I've seen
https://miaterati.tumblr.com/post/116920440576/i-decided-to-change-the-differential-before

Most others just say, oh it can be done, but you need to do work to make it fit.
As with any custom job like this, it is very hard to find the full story of what is needed like its a state secret or something.

Thanks Luke.
For now, as I am sure you can understand, I just want to get the car going again and do a few events, even if the diff ratio is not ideal.
I will look into the RX-8 option.
FWIW, I had though the car already had RX-8 suspension when I got it, but that may be only the front.

I believe the RX8 upright/hub is stronger (no broken hubs!), and has some other advantage in a competition car, possibly geometry. If I can remember where I saw it I will go back and check it out. It stuck in my mind because I thought of your car and wondered ...

Remembered, more or less: MT.net post on NC, there is not as much there as I thought, and no real hard information on the rear end