WHAT ARE THE APPROXIMATE HP/TQ LIMITS for VORTEC HEADS? well lets look at it!
approximate potential hp is found by this formula (.257 x max air flow x cylinders=potential hp) so .257 x 239 x 8=491hp potentially now figure about 90% efficiency is about max for most street combos and we get a reasonable figure around 442hp to shoot at, lets look at some combos,
STOCK vortec heads have a relatively small port size and 1.94" int/1.5" exhaust valves
valve lift figures over about .520 in mildly modifyed /clearanced heads or .450 in stock heads do little to increase flow, they were designed for massive torque in the 1000rpm-4500rpm range, minor mods easily increase flow to about the 4700rpm range, while EXCELLENT FLOWING HEADS FOR THIER PORT SIZE they are NOT RACING HEADS heres some combos useing vortec heads
from this sitehttp://www.ryanscarpage.50megs.com/combos1.html
keep in mind that torque peaks at almost exactlt the rpm where air flow efficiency peaks
Combo 73.
Combo 73 replaces the #441 heads and Edelbrock Performer RPM intake with GM L31 Vortec heads and an Edelbrock Performer RPM Vortec intake. The Vortec-style intake is needed because the Vortec heads feature intake bolt-holes that are vertical and not angled. A more aggressive cam is used on this combo. Another notable difference is that the Vortecs have smaller combustion chambers, which up the compression about 1.5 points. These upgrades produce 375 HP and 408 ft-lbs of torque.
Displacement: 350 cu. in.
Carburetor: Demon Speed Demon 750
Heads: GM L31 Vortecs, with 1.94/1.50 in. valves
Camshaft: Comp Cams Xtreme Energy 268, with 268/280° of duration, 224/230° of duration @ 0.050 in. of lift, and 0.477/0.480 in. of lift
Pistons: cast dished
Rods: stock
Crank: cast
Timing: 35°
Comp. Ratio: 9:1
MAX HP: 375 @ 5700
MAX Torque: 408 @ 4300
Combo 78.
Combo 78 comes from pages 65-68 of the April 2001 issue of Chevy High Performance.
GM Vortec cylinder heads are used with a Comp Cams Xtreme Energy 262° camshaft to produce 390 HP and 426 ft-lbs of torque. These numbers are made with 87 octane, while most of the combos on my site used 92 or 93 octane gasoline. Again, I am not sure how much of a power difference the lower octane makes.
Displacement: 355 cu. in.
Carburetor: Demon Road Demon 625
Heads: GM L31 Vortecs, with 1.94/1.50 in. valves
Intake: Edelbrock Performer RPM Vortec
Camshaft: Comp Cams Xtreme Energy 268° hydraulic, with 268/280° of duration, 224/230° of duration @ 0.050 in. of lift and 0.477/0.480 in. of lift.(Corrected valve lift with 1.6:1 rockers is 0.508/0.512 in.)
Rockers: Comp Cams roller, 1.6:1
Headers: Hedman Elite 1 5/8 in.
Pistons: Speed Pro dished
Rods: stock
Crank: Scat
Distributor: Pertronix HEI
Timing: 36°
Comp. Ratio: 8.75:1
MAX HP: 390 @ 6000
MAX Torque: 426 @ 4000
Combo 83 is much different than the previous two combinations. The heads are swapped for GM L31 Vortecs, and 1.6:1 roller rockers are used. A Holley 750 cfm carburetor is used, and the power jumps to 375 HP with 413 ft-lbs of torque.
Note that this combo is very similar to another combo from a separate test, Combo 78. Combo 78 has 2 less compression points and a slightly less aggressive cam, but it still makes 15 more HP and 13 more ft-lbs of torque. This is interesting, and it shows the variations between engines and dynos.
Displacement: 350 cu. in.
Carburetor: Holley 750
Heads: GM L31 Vortecs
Intake: Edelbrock Performer RPM Vortec
Camshaft: Federal Mogul, with 214/224° of duration @ 0.050 in. of lift and 0.472/0.496 in. of lift.(Corrected valve lift with 1.6:1 rockers is 0.503/0.529 in.)
Rockers: roller, 1.6:1
Headers: Hooker 1 5/8 in.
Pistons: Speed Pro forged
Rods: Federal Mogul
Crank: Federal Mogul
Distributor: HEI
Comp. Ratio: 10.6:1
MAX HP: 375 @ 5400
MAX Torque: 413 @ 4300
Combo 84.
Combo 84 takes the previous combo and swaps the cam to one with more intake duration. The result is a loss of 11 HP and 29 ft-lbs of torque. This loss is very large for only a 10° change in the intake duration at 0.050 in. of lift. The small increase in valve overlap usually does cause the cylinder pressure, and thus the peak torque, to drop. However, because of easier breathing, the peak power usually increases with such a change. The power increase did not occur with this combination though.
Displacement: 350 cu. in.
Carburetor: Holley 750
Heads: GM L31 Vortecs
Intake: Edelbrock Performer RPM Vortec
Camshaft: Federal Mogul, with 224/224° of duration @ 0.050 in. of lift and 0.480/0.491 in. of lift.(Corrected valve lift with 1.6:1 rockers is 0.512/0.524 in.)
Rockers: roller, 1.6:1
Headers: Hooker 1 5/8 in.
Pistons: Speed Pro forged
Rods: Federal Mogul
Crank: Federal Mogul
Distributor: HEI
Comp. Ratio: 10.6:1
MAX HP: 364 @ 5900
MAX Torque: 384 @ 4400
Combo 89.
Combo 89 replaces the L98 heads with L31 Vortec heads. These heads require a Vortec-compatible intake manifold, and an Edelbrock Super Victor Vortec single-plane is used with this combination. Apparently, this Edelbrock intake is similar to a single-plane GM intake, the Eliminator, with PN 12496822. This head and intake swap produces 20 more HP and about 380 ft-lbs of torque.
Displacement: 350 cu. in.
Carburetor: Demon 750
Heads: GM L31 Vortec, with 1.94/1.50 in. valves
Intake: Edelbrock Super Victor Vortec
Camshaft: GM steel roller, with 0.474/0.510 in. of lift.
Rockers: GM stamped steel, 1.5:1
Exhaust: Hooker headers and 3-chamber Flowmaster mufflers
Pistons: GM
Rods: GM forged
Crank: GM
Distributor: HEI
Timing: 32°
Comp. Ratio: 9.5–10.0:1
MAX HP: 376 @ 5600
MAX Torque: 380 @ 4700
Combo 99.
Combo 99 uses Vortec heads and a bigger cam than Combo 98. The heads are pocket ported, and this helps the engine to make 409 HP and 427 ft-lbs of torque. The torque peak occurs at 3500 RPM, but the power peak is at 6000 RPM. The torque peak is only at 58% of the power peak, instead of the normal 70-80%.
Displacement: 350 cu. in.
Carburetor: Holley 750 double-pumper
Heads: GM L31 Vortecs, pocket-ported, with 1.94/1.50 in. valves
Intake: Edelbrock Performer RPM Vortec
Camshaft: Comp Cams Xtreme Energy 268 hydraulic, with 0.478/0.480 in. of lift and 224/230° of duration @ 0.050 in. of lift.
Exhaust: Hedman 1 5/8 in. headers and Borla XR-1 mufflers
Distributor: HEI
Comp. Ratio: 9.4:1
MAX HP: 409 @ 6000
MAX Torque: 427 @ 3500
notice that depending on the cam and other parts used the engines all peak in the 3500rpm-4700rpm range now heres better flowing heads,on a 383 requireing more airflow, notice that altho the rpm range is similar the power potential is greater 
Combo 71.
Combo 71 comes from pages 84-94 the March 1998 issue of Super Chevy.
Combo 71 discusses a 383 cu. in. small block that makes 525 HP and 535 ft-lbs of torque. The engine has great heads, a very healthy street roller camshaft, and a stout bottom end. The camshaft has a lot of valve lift, with 0.614 in. of valve lift on the exhaust side and 0.592 in. on the intake. This engine is still very streetable—the compression ratio is only 9.4:1 and the heads only have 190 cc intake runners. With more of the racing treatment, this engine could have easily made over 650 HP. Of course, only street engines are shown here.
Displacement: 383 cu. in.
Carburetor: Barry Grant Silver Claw 750
Heads: Air Flow Research 190, with 2.02/1.60 in. valves, 190 cc intake runners, CNC porting, and extra hand-porting
Intake: Edelbrock Performer RPM
Camshaft: Comp Cams hydraulic roller, with 235/242° of duration @ 0.050 in. of lift, and 0.555/0.576 in. of lift (Corrected valve lift with 1.6:1 rockers is 0.592/0.614 in.)
Rockers: Comp Cams 1.6:1
Pistons: TRW forged
Rods: Lunati 5.7 in.
Crank: Scat 8060 cast
Timing: 36°
Comp. Ratio: 9.4:1
MAX HP: 525 @ 5800
MAX Torque: 535 @ 4200
THE SHORTER ANSWER IS VORTEC HEADS ABOUT REACH THIER MAX LIMITS AT 440HP/4700RPM 
