The 4.6L engine in my 2004 discovery overheated, misfired, and somehow made a gash through two cylinders making the block and one of the heads useless. There is a 4.0 engine in a junkyard near me. Is it possible to swap the 4.0 block and heads to the broken 4.6 engine so I still have the same displacement? If so, what is required? Do I need any special tools or parts? Will it be worth doing this for the power increase or should I just swap in the 4.0?

 

The block's are identical, the only difference is the crankshaft, connecting rods, and pistons. You can put the 4.6 rotating assembly in a 4.0 block with no issues, actually the 4.0 blocks are generally more reliable with respect to liner slippage.

 

Are the heads the same? For the process of putting the 4.6 rotating assembly into a 4.0 block, is it just plug and play to swap the parts over, or do I have to do things to prepare for it to work? I assume I need to change piston rings, but I'm not sure what else.

 

Heads are the same. If I were going that far I would certainly install new piston rings and also bearings. It's a plug and play swap as long as there is no worn in ridge in the cylinder wall; most are in good shape even with high miles.

Either a complete 4.6/4.0 is also a drop in operation if you find a good running used motor.

 

And the 4.0 from the wrecker needs to be a Bosch/Motronics engine. You can make a GEMS engine work, but there’s a lot more to it. (Engine needs to be from a Disco 2 or a ‘99-02 P38).

 

4.6 Range Rover P38 engine works fine, it is just plug and play.

 

Could my pistons have been damaged when the incident(s) happened?

 

Probably, you might need to replace that one.

 

IIRC, the AIR intake hoses and MAF housing are different (smaller) for the 4.0...the actual MAF sensor is the same....make sure to grab the intake hoses if available...

 

Since the 4.0 engine will be a 4.6 by the time I am done, is it fine to use the original 4.6 intake hoses and maf housing?