A correct turbo set up would gain sufficient boost at a low rpm. It all depends on turbo size and type. A larger turbo would act like the way you described but with two small twin scroll IHI turbos, that would give you some mean gains.

 

I'm guessing its going to be a twin turbo set up where there is one turbo for each bank/side of cylinders. However a sequential setup like the RX7 had would probably work like a champ for low end and high end torque transition.

 

Yeah I haven't decided on weather its going to be a sequential or just twin turbo yet. Routing both exhausts to one turbo is going to be hard, and with 2 GT15's they are going to spool instantly anyway. I'm planning on just flipping the exhaust manifolds and mounting the turbos on top. (2 passenger side manifolds)

 

This type of sequential turbos are used on the later RR's and are successful for initial and top end power. Out the outset they ran into some problems/difficulties but they are well sorted now.

 

My take, FWIW, is that the 4.0 twin turbo will be more exciting but problematical and the usual issues will prevail whereas MB diesel turbo is more reliable, longer lasting but less exciting to drive. Being I've done all the exciting driving bit I think I'd go for the MB turbo diesel.............I love oil motors and have now become a boring old f@rt who prefers reliability to performance.

 

The M617 is an "old engine" and 95% of turbo variant production came to the USA with auto transmission . (The normally aspirated units for the rest of the world). The engine was uprated in 1981 and phased out in 1985.

Not only is it "old " on specs but "old" in specification and power outputs emission etc --Good engine but nowadays a bit of an Ava Gardener now wizzen faced with sagged *****!

For an up to date MB power pack consider a Dodge Sprinter 5 cyinder diesel.
Plentiful parts and a lot easier to get than the olde M617 engine, plus it meets all Fed and Calif specs. I have one in a D2, using the NAG1 MB transmission al la Gelandewagen and close coupled to the LR T/Case.

Of course it comes with MB integrated PCM and Dodge Skreem module plus ancillaries to graft into the LR rig but is works quite well; with 26mpg US/gal and excellent acceleration leaving lots of stuff at the lights if that is your game.
Obviously makes the "Sport" domestic diesel truck crowd splutter as their stuff spools up, belches smoke and thinks about winding up the transmission to get a hard on and drive! I simply drive off like Fed Ex driver with lots of gray hair. No fuss no smoke and all very respectable like.
Should I state a Jay Lo or Beyonce style conversion with a nice tail----pipe that is !
But I am a bit old for all that at my age--I would be regarded as a dirty old man but I can still look!
Oyez que bueno!
T/V

 

If I went MB I would do a compound turbo setup and run 40 LBS or so. And turn the injection pump up to 11.

 

A 7.5 to 8.5 MM injectors on the injection pump would make that thing mean. There is a few videos floating around of a twincharged OM617 with 10MM injectors, and it was absolutely insane.