Originally Posted by: HK1837 
Hi all
Does anyone have any original HDT info that spells out what HDT did to the VH GroupIII engine? There is heaps of info for the optional 5.0L engine but not the 4.2L one. HDT claimed over 150kW for it, standard ones were only 115kW DIN with dual exhaust.
HK1837... from my HDT parts fitments listings, basically 4.2 and 5.0 GrpIII engines got the same mods (I say this excluding anyone asking HDT to do specials)
bar these -
4.2 engines kept the std valve size but DID get the revised HDT throating used on 5.0 engines
4.2 engines kept the std GMH inlet manifold (5.0 had manifolds port matched)
4.2 manual engines did not get the HD driven clutch plate
4.2 (all) and 5.0 auto engines did not get the modified distributor
all else.. exhausts, air cleaner, chrome items etc are all shown as being fitted to both
and curiously (or not!) no changes are shown to the valve train or camshafts (and timing chains) as fitted in the factory
note 4.2 and 5.0 engines had different Quadrajet carbs ex GM Holden but both are showing metering rod and
secondary rod changes for the factory parts
(IMHO, there is an error in the HDT listing... it says secondary jets are changed. That is impossible .. so I have said secondary rods which are changeable)
also the power rating is HDTs measure under the old 'gross' horsepower method I am thinking (no alt, water pump, pwr stg belt etc)
HTH
