I know it's not a massive difference, but if I can get the parts cheap, then why not? Being on 35s and armored up, it's just so slow. Obviously, it would still be slow with a 4.6, but if it makes merging on the highway easier, then it could be worth it. I'll try and see if I can find someone with a 4.6 to drive and compare how it feels to my stock 4.0, that's a good idea.

 

I used a shop out of SoCal that specializes in liners for LR blocks - Q&E. Would not use them to build though.

 

If I was in your boots I’d put in the 4.6 internals. Not quite apples to apples but my 4.6 GEMS P38 has considerably more power than my 4.0 Bosch D2.

 

Heads and block are the same for 4.0 vs 4.6. I put my old 4.6 Internals in a 4.0 block and everything worked. Pistons, rods, crank and cams are different between 4.0 and 4.6. I have read varying results on using 4.0 pistons in a 4.6. Some say its impossible, while others claim to have done it... Since the ECU between 4.0 and 4.6 are tuned differently, the car will run, but worse. You can reflash the ECU, but it would probably be easier to get a used one off of ebay.

 

When I rebuilt my 4.0 (and pinned the liners) I did a poor mans cam swap and put the 4.6L cam in it. seems like it has a little more pep, but clearly not like it would with a true aftermarket cam....but if anyone was wondering, it works just fine.

 

I'd consider looking at TWS Motors to source some parts. They're builds are extremely nice but really pricey, so not recommending them for a full build, but if you bought parts from them they would probably be happy to share info and recommendations. I know they work with Tornado Systems to do ECU re-flashes. You could probably pay them to send the ECU off and have it reprogrammed to be more suited to the 4.6 internals.

Having owned multiple 4.6 trucks and a 4.0 truck, I can definitely notice a difference but it is certainly not major. I can see how with a lift and armor any extra bit of power you can get would be nice. Would have been nice if they sold the 5 speed manual here in the US, that one extra ratio and less drivetrain loss from the torque converter would help acceleration a lot. I had a manual D1 and it was notable nicer and quicker on the road than a D1 with the 4 speed auto.

If I was in your shoes (and had some cash to throw at it), I would go with the 4.6 internals, reprogram the ECU, and consider a better exhaust header or at least a cat back system to take advantage of the reprogramming. I would also ensure taking into consideration that the 4.6 internals will generate more heat and pressure. The oil cooler from a 4.0 truck is a nice to have on a 4.6.

 

Thank you for all the info! I already had a set of long tube headers I got a good deal on I plan on using, and have no cats and an aftermarket resonator on it right now. Also my truck already has an oil cooler stock thankfully. The 5 speed d1s definitely felt faster, my dad had one at the same time as an auto and even with a higher mile motor, the 5 speed felt quicker for sure. And yeah I don't expect it to feel like a rocket ship with 4.6 internals, but anything extra could help. Mine scaled at a hair shy of 6k lbs, so it could use the extra power.

 

Before you spend all your time and money have you tried lighter wheels and/or tires? My D2 still has stock gearing but I did rebuild my 4.0 to 4.6 w/crower cam and when I run steel wheels with 33in MT its a lumbering, slow beast compared to running LR alloy wheels and good AT tires.

 

I'm on 17" BMW alloys and 35" MTs, but that won't be changing at all. I have a Honda I daily drive and a second d2 that's only on 31" ATs for light duty stuff, this truck is only for the hardcore stuff. But I don't have a truck and trailer, so I have to drive it to each park, most of which involve driving through the Appalachian mountains, so a power bump would be nice.

 

I don't drive our disco, my better half drives the disco. When it went down with a slipped liner I installed the 4.6 internals and cam into her 99 4.0 block.

Also did new rings, bearings (cam and crank /rod) and lifters.

Once back on the road she had no idea what I did other than fix the liner tick but the report was "wow this is faster and I'm getting better fuel milage"