Fun on the Flow Bench
Besides dyno testing the new Vortec Bow-Tie heads on a ZZ4 crate engine, McLaren performance also put them on a flow bench. Not surprisingly, the high-velocity, high-volume design of the heads produced very good numbers. The heads used in the test were early production examples, not prototypes. So, results should be similar with off-the-shelf parts.
Here's how the numbers looked on the intake side:
 
SMALL-PORT HEAD
Lift CFM
0.100 67
0.200 136
0.300 182
0.400 223
0.500 251
0.600 240
0.700 240
 
LARGE-PORT HEAD
Lift CFM
0.100 63
0.200 134
0.300 181
0.400 227
0.500 258
0.600 255
0.700 261
 
The heads are comparable until about 0.400-lift, where the runner size of the large-port head really starts to pull its weight. For comparison, we've seen flow numbers on the Edelbrock Performer RPM aluminum heads that show a intake maximum flow of around 228-230 cfm. The Performer RPM had 64cc chambers, 170cc intake runners and 2.02/1.60 valves.
In our opinion, the iron Vortec Bow-Ties performed extremely well on the flow bench. In our opinion, the iron Vortec Bow-Ties performed extremely well on the flow bench.
SOURCE
GM Performance Parts
www.gmperformanceparts.com
McLaren Performance