VORTEC HEADS

GM Bow-Tie Vortec PN 25534431 $580 each
Intake runner: 206cc
Combustion chamber: 65
Intake valve: 2.00-inch
Exhaust valve: 1.55-inch
Maximum valve lift: 0.545-inch
Material: cast-iron

GM Bow-Tie Vortec PN 25534421 $550 each

Intake runner: 180cc
Combustion chamber: 65
Intake valve: 2.00-inch
Exhaust valve: 1.55-inch
Maximum valve lift: 0.545-inch
Material: cast-iron

All concerned will be delighted to hear that the head includes intake manifold mounting holes for both early-model six-bolt and late-model four-bolt Vortec design. Mandated GM intake manifolds include a raised runner-type PN 10051103 (six-bolt type) or Vortec design PNs 12366573, 12496820, 12496821, 12496822, and 12499371 (four-bolt type). Though production cylinder head and intake manifold gaskets are acceptable, the hot squeal is Fel-Pro (PN 1142 for the MLS and PN 1289 for the intake). As per Scoggin-Dickey, pricing is: small port 4421 complete, $499.95; small port 4351 bare, $269.25; large port 4431 complete, $539.95; and large port 4371 bare, $293.25.

Differences in the intake ports are dramatic. The new design is taller, narrower, flows straighter into the valve, and has a 206cc volume (L31 ports are 170cc).	The old port has 30-year-old technology (see Flow Chart).	The new combustion chamber is markedly different than the old.

2.02-inch intake valves and 1.60 exhausts--with a 2-angle 45-degree valve job and no back cut on the exhausts.	New Bow Ties are the best 23-degree iron heads on the market."	GM Bow Tie port has definite D-shape, is raised up, and has a 77cc volume.

Original L31 Vortec casting. The new heads carry PN 25534371	New GM Bow Tie Vortec The 4371 castings have a much thicker deck than the previous Vortecs	The L31 exhaust port (top) looks like old tech;

Vortec Bow-Tie Brief
There are two versions of the new GM Performance Parts Vortec Bow-Tie cylinder heads: This one, PN 25534371 (bare) and PN 25534431 (complete), with the larger ports, and another with smaller ports, PN 25534351 (bare) and PN 25534421 (complete) with 185 and 65cc volume, otherwise, the architecture and improvements over the L31 design are the same. We will test the smaller version very soon in a dynamometer exercise. We were able to get an exclusive look at the big-port heads just as they were used in a NASCAR-type application.

Out of the box, they feature revised intake and exhaust ports and are machined for a 2-inch intake and 1.55-inch exhaust valves. The deck surface is 0.045-inch thicker than the L31s, and it has 65cc combustion chambers, a 206cc intake, and 77cc exhaust ports (see Flow Chart). The head is also machined for 3/8-inch screw-in rocker studs and a large valvespring pocket, and it will accept up to a 0.530-inch lift camshaft without modification. These castings are identified by the Bow-Tie logo below the exhaust port and the Vortec logo on top of the intake port area. The GM logo is also cast into the bottom of the intake port runners.

4000 RPM

431 TQ

328 BHP

5500 RPM

373 TQ

391 BHP

OE Vortec: PN SD8060A

Combustion chamber: 65cc
Intake runner: 170cc Intake valve: 1.94-inch

Exhaust valve: 1.50-inch

Advertised Airflow Measured at 28 inches of H20
Lift	Intake	Exhaust
0.100	66	57
0.200	129	101
0.300	186	136
0.400	219	149
0.450	225	150
0.500	216	155

CLEAN UP PORTED

4000 RPM

434 TQ

330 BHP

5500 RPM

377 TQ

394 BHP

Advertised Airflow Measured at 28 inches of H20
Lift	Intake	Exhaust
0.100	72	57
0.200	135	103
0.300	192	140
0.400	223	159
0.450	237	163
0.500	231	170

4000 RPM

434 TQ

330 BHP

5500 RPM

381 TQ

399 BHP

GM Bow-Tie Vortec PN 25534421
Intake runner: 180cc
Combustion chamber: 65
Intake valve: 2.00-inch
Exhaust valve: 1.55-inch

Advertised Airflow Measured at 28 inches of H20
Lift	Intake	Exhaust
0.100	71	53
0.200	139	102
0.300	182	131
0.400	224	146
0.500	248	161
0.550	250	164
0.600	240	165

5500 RPM 503 TQ 527 BHP

7500 RPM 443 TQ 632 BHP
GM Bow-Tie Vortec PN 25534431

Intake runner: 206cc

Exhaust runner: 77cc
Combustion chamber: 65
Intake valve: 2.00-inch
Exhaust valve: 1.55-inch

Large-Port Vortec Cylinder Head Flow
INTAKE		EXHAUST
Lift	Volume	Lift	Volume
0.200	128.6	0.200	100.8
0.300	188.4	0.300	138.6
0.400	234.8	0.400	154.4
0.500	257.2	0.500	152.5
0.600	263.2	0.600	163.8
0.700	269.1	0.700	167.0

4000 RPM

423 TQ

323 BHP

5400 RPM

373 TQ

384 BHP

Dart OE replacement Vortec
Intake runner: 165cc
Combustion chamber: 67cc
Intake valve: 1.940-inch
Exhaust valve: 1.50-inch

Advertised AirflowMeasured at 28 inches of H20
Lift	Intake	Exhaust
0.100	NA	NA
0.200	126	108
0.300	185	128
0.400	221	136
0.500	232	138

4000 RPM

437 TQ

333 BHP

5500 RPM

390 TQ

408 BHP

Edelbrock E-Tec
Intake runner:170cc
Combustion chamber: 64cc
Intake valve: 1.94-inch
Exhaust valve: 1.55-inch

Advertised Airflow Measured at 28 inches of H20
Lift	Intake	Exhaust
0.100	64	54
0.200	130	104
0.300	186	140
0.400	220	169
0.500	232	183
0.600	238	190