OK - you asked for it - here is the whole conversation - great info. Part 1:
The ( Hammil ) Builds Involved Using the crank, rods and heads from a D1 or 4.0 D2 and a custom grind cam, along with Bee hive or short coil valve springs to prevent coil binding,, Special machine work on all of the sleeves after first decking the block.. I personally like the pan and front cover set up on a D2 better than the steel pan on the D1,But it also depends on which truck you are putting the finished engine in.. You can change the bore slightly and have forged pistons custom made for less money that stock rover parts, There are 4 or 6 tricks of the trade that can be done this way and you end up with a very low residual friction engine, that makes 90% of available torque only 300 or so rpms off of idle ,climes to 100% and then holds that torque up to about 4,000 rpm after that they go a bit flat.. They end up being extremely durable ,and drive out like a coiled spring on the low end.. The builds is expensive to do, The D1s and D2s may be getting to old for this to be practical any more.. But would still be very viable for a 90 or 110.. It will work Gems or Bosch either way..
Well I think most guys think they should build for horsepower, When realistically what your really need with this sort of vehicle is useable torque.. I Have built a couple dozen highly modified engines, looking for only 2 things, (1) useable torque, and Durability.. This is a really great way to go except for the guy that wants to tow a Fairley heavy trailer at 70 MPH, You have to sacrifice the high end a bit in order to get the low end torque.. If you are ok with that and don't mind not having high side gains this will be good for you. .But if you want an increased high side you should do an LS swap.. With Gems and Bosh aside, the late 4.0 and 4.6 blocks are identical, The only difference is that by that stage Rover was owned by ford, and some thing were already slated to be discontinued, To bridge the gap ford Invested is sonogram testing equipment, and every block was tested by hand, the testing was somewhat subjective, and resulted in the block being identified by simply putting a dab of paint on the engine block Vallie above where the cam runs, The best of the blocks with the least amount of core shift were chosen to become 4.6 liter engines, ones that did not make the cut for that became 4.0s and ones that did not make the cut for that became new replacement short and long blocks both 4.0 and 4.6..Yep the sold the worst of the blocks as new replacement engines... Go figure why so many were prone to failure???
So in theory if you are building an engine a 4.6 that has never been replaced with a factory new short block should be the best block to choose, But at the same time that block has been tutored with the heat produced by the 4.6 builds.. Guys don't really understand the thermodynamics involved... A 4.0 and 4.6 have exactly the same bore and even run pistons and ring sets with the same part numbers; to get the extra .6 liter the 4.6 has a longer stroke and as such shorter rods, Which in turn messes up your rod to stroke ratio which is a whole other story about what not to do when designing an engine.... Just sticking to the thermodynamics for now, the crank and rod configuration in a 4.6 allows the piston to be powered father down the cylinder sleeve, and actually allows the (Fire deck ) of the piston to be shoved down into an area of the block that is no longer exposed to cooling water on the outside, as a result, ( ON PURPOSE, AND WITH FULL UNDERSTANDING OF THE ENGINEERING STAFF ) that small area of the sleeve routinely ran as a hot spot under load..
This caused thermo stresses in this area of the block that eventually end up causing swelling and or the start of a thermo crack. This is basically why most of the 4.6s ended life with slipped sleeves, Usually on the 2 or even 4 rearmost cylinders, as they were farthest from the water pump and could run quite a bit hotter.... In short, a 4.6 Block was the best of the blocks available when the left the factory, But after being exposed to thermo stresses for 100,000 miles maybe not so much.. If you already have a 4.6 block it is definitely worth cutting out the rearmost sleeves, then hitting those counterbores with a sunet hone, just ever so slightly, in an effort to just clean it up enough to measure the ID at several places while keeping careful notes, And also looking for cracked areas running vertically, up the back side of the aluminum.... Generally speaking although a 4.6 block was in theory a better block when in left the factory, a block from a well maintained 4.0 will be in better condition and is a better candidate for a new build.. I Have all of the information in my notes someplace, but I could not put my hands on them easily, I will try to look them up if you have more questions.. But anyway there were I think 4 generations of Buick / Rover alloy blocks.. Very early blocks had 14 head bolts per side which did not work out so well, early blocks were also 2 bolt main cap configuration and early blocks had NO reinforcement across the cam Vallie.. If you plan to keep the rig indefinitely, I would start with a block that was originally 4.0 or a very well checked out 4.6 You will want a block with 10 head bolts per side, 4 bolt main caps and the 3 cam Vallie braces.... If you hold it to 4.0 liter you can actually builds a really good and very durable engine for a D1 or D2..I can give you more details later if you want...