Okay.. I know this has been covered quite a bit and a few have done it, but I can't find anything. I have an 02 Disco with a Bosch 4.0 engine without the secondary air. Man... it's a dog. I'm just about to flip 260,000 miles. YAY.. I'm never getting rid of this thing, I love it! I've swapped out the transfer case to an 04 transfer case. Now, I think I want to upgrade the engine to the 4.6. Question is... since I don't have secondary air, if I dropped in a 4.6 would I have to add the secondary air or can it be swapped without it. I believe all 4.6's had secondary air.
Is there a noticeable gain in power from the 4.0 to the 4.6? Or would a fresh 4.0 be good enough. I think I'd have to replace the ECU with a 4.6 ecu. Any guidance, thoughts..?...

 

A heads up.... if you go with the 4.6L engine .... you may need to replace the 4HP22 with the 4HP24 to handle the additional torque

 

If you have a good block you can swap internals over from a 4.6 into the 4.0 block and just need a 4.6 computer I believe. No issues with SAI from my understanding when going this route. Also a good time to try and swap in a cam and squeeze a few more horses out of the motor.

 

Not all 4.6L engines came with SAI. I've worked on a 2003 that didn't have it.