10% power hike is probably optimistic, hugely so. But the cams and followers do wear, so replacing a worn one with a new one will make a big difference.
All you need to do is look at the figures. An EFI 3.5 is 165hp and a 3.9 is 182hp.... if all you had to do was put the 3.9 cam in the 3.5 to gain 16.5hp (181.5bhp). Why did Rover go to the expense of adding an extra 0.4 litres of displacement. These figures would also suggest that 0.4 litre is only 0.5hp extra over the cam swap, which just doesn't make any sense at all.

That's why I used the term allegedly, although in my experience there can be disparity between figures & real-world driving experience.
I will however stand by my advice re. stroking the 3.5efi as I knew the LR mechanic who carried out the rebuild on his Classic. He was in the habit of towing a large twin axle caravan & needed more grunt but didn't want to go for a 94mm bore V8. Grunt it certainly did, to the eventually detriment of the HP22 'box :rolleyes:

Another choice might be an ECU remap ?
 
That's why I used the term allegedly, although in my experience there can be disparity between figures & real-world driving experience.
I will however stand by my advice re. stroking the 3.5efi as I knew the LR mechanic who carried out the rebuild on his Classic. He was in the habit of towing a large twin axle caravan & needed more grunt but didn't want to go for a 94mm bore V8. Grunt it certainly did, to the eventually detriment of the HP22 'box :rolleyes:

Another choice might be an ECU remap ?
Stroking the engine is fine, no issues there. But you are talking quite a bit of money and effort. No idea what the bits cost these days, but I suspect a lot!

BTW - if you stroke the 3.9 you get 4.8 litres and even more power and grunt than the 4.3.... but for the same basic cost.
 
Thanks peoples for all your input, genuinely appreciated.
Not been on here for a while for one reason or another. Still cant decide what to do......
 
BTW - if you stroke the 3.9 you get 4.8 litres and even more power and grunt than the 4.3.... but for the same basic cost.
And the chances of a slipped liner .. ask me how I know :rolleyes:
I would vote for retaining the durable 3.5efi & going for a top end overhaul with uprated cam.

Incidentally it's not just the engine output to consider when it comes to towing with a RRC .. allegedly (that word again) LR fitted the smallest of 3 torque convertors from the factory, might be worth seeking advice on transplanting a larger TC with a lower stall point, together with HP24 internals for enhanced durability.
 

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