I don't have the 454 boosted yet, it will be. I've got two Vortec 454's, one in the truck the other one on a stand in the garage. The second one will get bored and stroked to 489 CID with forged parts, the top end will be Trickflow oval port heads with stainless roller rockers and a Lunati cam. On the exhaust side, hooker longtubes with electric cutouts. A stock intake manifold with 62# injectors is being modified with an intercooler mounted over it to be fed by a Whipple W200 (3.3L) compressor mounted on the passenger side. This will be driven by a dedicated 8-rib belt, the crank pulley for which I just got today actually. Running a 2-bar tune and 9-10psi of boost I expect 850HP from this.
I've been driving around with no boost for 14 months now and it's taking a toll on my happiness and sanity! I miss the sound but I miss the stupid amount of power that 383 made with the W140 on it most of all!

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"James B." '99LT_Tahoe4Dr2WD, Tuned L29 Vortec 454, 62#Injectors, Cutouts, 4L80-E 10.5"14bolt ,EatonPosi-4.56:1, Gear_Vendors, HydroBoost, (NEXT: Brodix heads, 230/240 cam, SS roller rockers, longtubes, THEN: Intercooled W200R-8psi in the future...)