The turbo block has two vents for the lifter chambers of the block that the non-turbo does not have. Figure 1
shows the rear lower extremity of the “V” of both blocks. The non-turbo
block is plain and just follows suit with the rest of the casting. The
counter bored and threaded hole (red circle) is where the camshaft
thrust bolt is installed. The turbo block on the right has a cast and
machined turbocharger mounting flange in the rear of the block at the
bottom of the “V” with oil feed and drain back in between the mounting
bolt holes. In the rear of the blocks you can see the last cam bearing
bore and the main oil galley plug threaded bore just above it and you
get a better view of the breadth of the mounting boss.
You also need to pay attention to the #1 main bearing housing bore
register in the block. If it has a center bearing tab locator (Figure 2)
you will use the three hole main bearing since that register also has a
groove cut into it. If it has the offset bearing locator tab in the
main bearing housing bore the block will have a plain single hole main
bearing bore register.
Turbo blocks also have piston-cooling jets/nozzles that feed off of the main bearings (see Figure 3). You may find non-turbo blocks that have been machined for these nozzles but actually have plugs installed.
Early 3208 non-turbo blocks had a slightly steeper main bearing cap
parting line angle. I was unable to determine a serial number break as
to when that happened but if you’re salvaging main caps for block
repairs you will want to be aware of it (see Figure 4).
One worldly piece of advice on main caps: they need to be tight in the
register in the main saddle. If you have a cap that is loose (one that
slides in and out with little or no resistance), it has stretched and
is out of round. If you have a main cap that is “kind of” loose but
still measures in spec, you will probably have a premature main bearing
failure at that location. If the caps are tight enough that you need to
struggle to get them out of the register, preferably having to wiggle
them back and forth, you will be perfect.
If you need to, reclaim the register area of the cap and mill the
register face back to a dimension that will keep the cap good and tight
in the block register. Then align bore the block, but remember that you
have a stacked gear train with this engine, so you shouldn’t be moving
centerlines if you want your gears to work.
I know that this information is a “feel” dimension and I have not given
you a specific press fit but I am unaware that there ever was a
published specification, I can only share a “school of hard knocks”