| GM Vortec |
| Valve | Exhaust | Exhaust | Open |
| Intake | | Lift | w/ pipe |
| 0.050 | 40 | 25 | 25 |
| 0.100 | 70 | 48 | 49 |
| 0.200 | 139 | 101 | 105 |
| 0.300 | 190 | 129 | 137 |
| 0.400 | 227 | 140 | 151 |
| 0.500 | 239 | 147 | 160 |
| 0.600 | 229 | 151 | 162 |
| E/I | | 62% | 66% |
| GM VORTEC IRON 855 |
| Port: | 170 cc |
| Chamber: | 64 cc |
| Valve Sizes: | 1.94/1.50 |
| I Flow @ 0.400: | 227 cfm |
Here is perhaps the sleeper head among GM's factory castings. According to our sources, this head was designed after the LT1 aluminum head and offers better flow than the LT1 but only on the intake side, which we confirmed with our flow-testing. This Vortec truck head is also the same head used for the iron LT1 engine used in the Impala SS, just with a different intake-manifold-bolt pattern. Compare the Vortec flow numbers to the LT1, and you'll see the Vortec moves some air, especially in the midlift area. The small chamber will produce an increased compression ratio with an engine of 350 or larger, but that should work fine with race gas. This is a good head for situations in which iron heads are required. This Vortec head even outflows the now-antiquated iron Bow Tie head!