hey guys and gals i'v got a 4.2 with the howell tbi kit i was thinking of putting a spare turbo i have on the motor i dont know to much about the internal's of the 258 or if the tbi setup could handle the extra fuel requirements any thoughts would be great    thanks  

you should be able to run about 5 psi without any problems. depending on your CR's  

really i heard that the gm map sensor is good to 30 psi but i didnt think the tbi computer could add extra fuel for boost   so am i to guess pretty much i'm almost set fot the fuel aspect  ? is this the same tbi setup as the 4.3 turbo off of gm's early 90's blazers ?  

that may be but it take a bunch of tuning and lower compression to run 30#'

the 4.3 turbos are a rare bird,  

hell 5 psi sounds more then fair to me so do you think i'll have to do much tuning to account for the 5psi or the tbi will handle the fuel and i'll just have to dial back the timing to pervent knock  

using the low boost the computer may control the timing on its own to a point.