GMMAD has pretty much covered it. I have just built a fresh 350 for twin turbos going into a 68 Mercedes ( yes I know Im messed up!). Anyway here's what I did:
roller rockers, high tensile rod bolts, hypoeutectic pistons (need to get compression down to around 8.5-9:1), cam, valve spring upgrade, high volume oil pump (since my turbos are oil cooled), enlarged plennum, larger injectors (Im using a tuned port injection manifold, yours MAY not need it) and cam.
On the flip side, I have seen an LS1 twin turbod with stock block and heads (only mods were the injectors and computer) and running 14psi without problems however it blew a water line and you can imagine what happened.
Just remember though, its the same with superchargers...more air, more fuel, bigger bang, less engine life.
The other to consider (and its a pretty decent expense) is you will need a computer upgrade or mega dyno time to reprogram your stock computer - around 7 hours for a stock ecu, because the ecu's "brain" can only be programmed once. So the process involves getting the car on the dyno, setting up what looks close to right on the computer, then burning a new ecu chip, then try it out, make changes, burn a new chip, fit it and try again. Then if you change to larger or smaller injectors then you have to go through the whole proces all over agian.
Haltech make a great ecu (E8 or E6x) that will controlled a TT v8 holden nicely and the changes can be made "live" without having to burn a new chip everytime. It simply interfaces straight into a laptop and you can change whatever you need to.
If you're doing the mods yourself, bank on spending at least $3500 and if you get someone to do it, then at least $5000. Its a fair outlay and Im guessing that's why so many people go to a supercharger setup.
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