5.3 Silverado
If you want to keep the 5.3 and keep it N/A, get the best aftermarket heads money can buy and call a sponsor for a matching cam. Also 1 7/8" longtubes, 3" true duals, underdrive pulley, Fast LSXrT intake, electric fans, and an excellent street/dyno tune. 400rwhp is a more reasonable but still lofty goal.
If you don't already have them also plan on a built trans, 3600+ rpm stall, and some gears.
Thunderstruck's recommdations are spot on. Good heads, full bolt ons, good towing cam, etc. figure you're $4K in at that point. You're only $2K away from buying a 6.2L crate engine. If you're set on the horsepower and NA, then swap in a used bigger motor and start with a better foundation
Supercharging with a roots type like magma charger, not centrifugal, might be a very good option for your who goals, even though you said you don't want it.
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N/A is going to be a lopey, high stalled, pain in the *** that makes a large impact on fuel mileage and still comes up well under your HP goal. It probably won't be impressive in the low end and will need to rev hard to hit it's power potential.
Turbo will get you power and drivability and MPG efficiency but my own personal experience leads me to regard turbo vehicles as relatively unreliable and full of headaches so I would not want to dick with one for a daily driver.
Supercharger will get you loads of power/tq from off idle to the upper RPM and when you drive like a sane person remain relatively docile and efficient and you might actually hit your HP goal too. A magnacharger or similar like mentioned above is the best answer to this situation based on the information I have so far.
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My Gto had a maggie and it was a blast, makes loads of power right off idle if you want it to, or you can cruise around at part throttle and you'd never know it had a blower.
Still might be difficult to get 450 wheel with a 5.3 unless you pulley the **** out of it or you find a newer tvs head unit






