i dont see the point in putting a smaller motor into a big car. yes they came out with the rb30 but most wish they had 4.2s.
rb30 will not give anywhere near the low down torque of a 5l even turbo'd you would be struggling there,
also you can make a 5l go pretty well pretty cheaply. and the conversion has been done to death so getting parts is pretty easy.
probably as with the chev but rb30 needs engine mount mods to make fit.
imo go the 5l
Do a search,theres plenty written comparing the TB42 to the RB30
Do a search also on the 5L conversion,if your handy with the spanners doin it yourself will save heaps,theres even a few on here that are doin the 5L conversion for only a few K all up
4.2 or larger
Dont go backwards in cubic size
The Holden conversion is probably the easiest to do with a Patrol, as just about all the engine components fall on the same side as the Patrol engine (even the air cleaner is the same). Plus, all the parts necessary for the conversion are readily available eg gear box adapters etc.
ive had a few rb30 skylines and there a pretty good thing but even in a 1400 odd kg body there not exactly a torque monster. ive had gqs with a 4.2 efi, a 5l vn motor, a mild 383 stroker and a pretty full house 383 and the difference between them all was amazing.
to be honest i dont think even the 5l has enough torque for the size of a patrol- especially if your gonna go bigger tires and a few accessories- mine had 35s and bars and came in at 2400kg.
When i went to the stroker, i actually found it didnt effect economy too much because it had such an easier time of getting around and all the engines got around the 20 to 23l/100 mark around town. i also ran gas injection to make them affordable and it made the same power as petrol and very similar economy to that'd be a good way to go too.
And on the power front the tb42e made low 70's kw atw and cant rem. the torque,
the 5l 109kw at like 4500 and under 400nm,
the first 383 171kw at 3800( stock manifold) and around 600nm
and the full house 383 made 235kw at 4900( come racing manifold) and 680nm at 2800 and over 600nm from 2000 till 4100 with a baby cam- great off road.
So for me from what ive felt and seen the more cubes the better!
I have just done a 5 litre conversion and to be honest if someone wanted to upgrade their RB30 or TD42 model I would deffinately consider a trade hey. Not that the 5.0 is lacking in anyway, it sounds great and goes pretty good for a stocker, but I have a better record for building tuff RB's over the years and this is my first V8 (customising & the costs involved to supercharge/turbocharge or stroke it out is killing me). I would rather an RB30 with a RB25 head, decent turbo etc. Parts are cheap & easily sourced without having to fabricate it all yourself...