IDK if I'm putting this in the right section but whats out there for the OBS 5.7Ls? I have a buddy that wants to keep his 350 like H/C headers exhaust stall but what gains can he really get?And how can it be tuned? thanks

 

what year is it?

 

Bingo. We need to know if it's toilet bowl injected or the ever wonderful Vortec CSFI.

 

its a 1991

 

Oh it's not so bad, lol. The heads, intake and cam and entire exhaust system in the TBI trucks are junk if power is what you are after.

Goals are the biggest thing I guess. And he will need to spend some dough to keep it TBI and support any amount of power. Most guys switch to a high pressure pump ( Like a Walbro 255) and then regulate it down to whatever you need. The more pressure you put behind the injector the more it flows. And switching to a 2" base on the throttle body portion itself is a good idea.

Some say use the 454 TBI ( 2" bore on the base)..... and that is fine if you can get one. Even so they don't flow enough fuel to support a ton of power either with only 13 psi behind them.

The larger injectors that they use almost become a must though. 80 pph injectors with 20 psi behind them can probably flow enough for around 400 HP. Then you basically will want that pressure vacuum referenced so it doesn't choke itself to death at idle.

Go to www.thirdgen.org for more TBI stuff. That is where the info is at if you want to play with it.

Tuning, well I would learn how ( like anything else I do) and use this:

DynamicEFI

Otherwise you need to buy a socket, blank chips and start burning them. Waste of time nowdays IMO. 91 should still be rocking the old 7747 ECM and it's pretty well supported.

Heads, cam, intake, stall and whatnot are dependent on weight, intent and goals, just like anything else. It's a Chevy 350 in there....... you can buy anything you can think of for them. Hopefully it's a roller block ( not all 1 piece seal blocks are) as the TBI truck V8's all ran flat tappet cams stock. If not just get a Vortec block ( casting number ending 880), or an ending 638 casting number 1 piece block and add the roller goodies.

The Vortec truck engines are all roller cam. As are all passenger car TBI engines or TPI engines. You can probably find enough wrecked engines in a pick and pull to get the cam retainer plate, spider assembly, lifter retainers and even lifters if you want from. Probably LT1's too or the Caprice L99 4.3 LT style engine.

LS and Gen 1's use the exact same roller lifter BTW.

It would be cheaper to LS swap the truck if he wants to make power nowdays, but if this is what he wants, it still can be done!