Internally, they are hugely different. Some Def things are... 1z/AHU injectors are set at a lower pressure... ALH are set at 220bar if memory serves me correctly. Also...internally, the pistons of the 1z are 1piece, cast units similar to the IDI TD pistons... 1z pistons also have a top ring that sits higher up on the piston than on the AHU/ALH engines...
With the AHU engine introduction the TDI pistons saw a significantly strong alloy introduced, brass triuons and thicker rings lands compared to those pistons in the 1z.
The blocks of the 1z and AHU are the same... very similar to the blocks used by VW for almost 30 yrs... mounting bosses for MK1, MK2 MK3 apps, all exist on both 1z and AHU engines... the water pump is external from the motor and belt driven
The block of the ALH was changed and lost the MK1 mounting boss for all four bolting mounts. The block is slightly longer in the main run than the 1z/AHU units. The block is supposedly "reinforced" in the ribbing more but uses the same internals as the AHU (1z exception because it has the cast pistons).The vac. pump is relocated and no longer the traditional vac. pump that is driven off the int. shaft on the earlier 1z/AHU motors and the water pump is internal, driven off the timing belt. The head is also different on the ALH motors, with the new block it has a wider "central galley" oil return in the head vs. the 1z/AHU built on the older style block that has a central relief galley and one that sits to the left on the front of the head as well. The valve cover on the 1z/AHU mounts similar to the AAZ cover (3 stud mount) whereas the ALH cover is all cast aluminum and mounts with several studs
Lets see...what else... well, 1z/AHU motors use a slightly different configuration for the injection pump.... a 7 pin pump vs. a 8pin (correct me if I'm wrong) on ALH pumps. Also, 1z/AHU motors use the traditional sprocket drive for the injection pump with a fixed sprocket . The ALH introduced the use of a pressed on hub to the pump and an adjustable sprocket that bolt to this up that allows for initial timing adjustments to be made WITHOUT having to take the pump loose at the front flange and back retaining bolt (like you do have to do on old IDI motors as well...)
The 1z/AHU was rated with 90hp and 150ft/lbs...the ALH 90hp and 155ft/lbs
1z/AHU used a wastegated Garrett turbo that was fairly small and with the ALH the movement was made to the use of the VNT 15.
As far as performance. Flat out...there is more programming options, etc. for the ALH just off the shelf...on the market. 1z/AHU programming for the electronics end of them....not so much. Also, the ALH engines are supposedly able to support more hp/tq as well. However, several nice AHU and 1z's have been built up (in my case, I did a 1z, but I replaced the weakest link...the pistons with modified ALH units) and perform very well... in many ways, I think easier to maintain with the external water pump, etc. Read about stories of those with ALH's that have had the water pump go and take the timing belt with it and in turn, wrecking the head, pistons, bent valves, oye.... lots of stuff. Most cases of that though is owner neglect...not paying attention to maintenence.
I'll reread to see if I missed anything
think i got most of it though..
Joe