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