15L V8 Discovery 2

Being realy stupid here but i have tried finding info on this online as to the maximum engine size in litres you can legally drive on the road in something like a d2 or a defender, obviously after it passes an engineers report and all the rest of it. or is it whatever you can safely fit in while sticking to all the other regulations. any help would be much appreciated as i have some bits lying around that may get frankensteined together. many thanks

I don't know the French laws, but I'm expecting the engine bay will limit you before any law will.
What are you hoping to fit?

In an SD1 Pics of 27 litre Rolls Royce Meteor engine installation. - Page 1 - General Gassing [Archive] - PistonHeads UK
and:
Petersen 27 Litre Meteor | petersen-engineering (bobpetersenengineering.co.uk)

Ratae said:

In an SD1 Pics of 27 litre Rolls Royce Meteor engine installation. - Page 1 - General Gassing [Archive] - PistonHeads UK and Petersen 27 Litre Meteor | petersen-engineering (bobpetersenengineering.co.uk)

Click to expand...

May not concern you, but the Merlin & Meteor have different rotation though I'm not sure of which goes which way.

Both have been used in cars so there's obviously a workround to solve any issues.

Ratae said:

Both have been used in cars so there's obviously a workround to solve any issues.

Click to expand...

With shaft drive motorcycle engined trikes the rotation is often wrong - many people have built something with 5 or 6 reverse gears. Simple solution is to turn the axle upside down, although to do it properly you also need to muck about with level plugs and breather adaptations.

From the look of this page at the DVLA https://www.gov.uk/vehicle-approval/individual-vehicle-approval as long as your vehicle isn't above the weight limit for a car (3.5 tons?) after conversion and passes a statutory IVA test you should be OK. The manual is linked on one of the other pages and I have been told it is a good cure for insomnia.