well, IMO i think the only difference internally between the NA 3.1 and the Turbo 3.1 are the pistons and the oil pump. the heads (combustion chambers) are a little different however some '89 NA 3.1s got those same heads. the camshaft is the same as the NA 3.1. the connecting rods are the same. some people say the crank & block are stronger but there is no proof to back that up (at least i haven't seen any).
i bought a complete Turbo 3.1 for $350 from a local salvage yard. the engine came from a white TSTE. i pulled the heads and found a melted piston :( soo....i decided that i would just turbocharge the existing NA 3.1 in my 227,000 mile Cutlass! it runs great, so why not just throw all of the turbo parts on it while i get the 'real' TGP shortblock rebuilt?
i took the TGP heads to a machine shop for a valve job and new valve seals, cleaned the heck out of the engine, i'm installing a new Melling 95HV oil pump along with new gaskets and seals everywhere. then i'm bolting all of the external TGP parts onto it like the rear manfold, crossover (which was also rebuilt), turbo etc. i've already put the TGP radiator & intercooler in the Cutlass. i'm using a TGP engine wiring harness and have a modified TGP/5-speed chip coming from Jay so that takes care of electronics. i'm using a manual boost controller (grainger valve) and i won't run over 8psi with it. i think it will last until my TGP shortblock gets rebuilt. and if it doesn't, oh well i still have my other car i can drive :)
i agree with the others here about buying TGP parts seperately....i spent ALOT of money buying the TGP parts individually and then i found the complete TSTE engine in the local salvage yard for about half the cost. i ended up with enough parts to turbocharge two 3.1s!! (most of those extra parts are now sold however). definately buy a complete TGP engine if you can....better yet buy Skalor's Lumina! $800 is a helluva deal IMO.
good luck
