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Originally Posted by Captainfab
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That's a great site and the reference I use often
Vortecs: 230/148 @ ~.475
Bowtie/Small: 245/160 @ ~.500
Bowtie/Large: 260/165 @ ~.500
Note that although the flow isn't all that much higher on the small-port bowties, the intake/exhaust ratio is FAR better. You can also see that lifting these heads to the moon doesn't buy much.
Also note that all Vortec designs have far better low- and mid-range flow than even most tier II heads.
There are two aspects to head selection: flow and intake runner size.
First selection is flow, and that's based on the HP you want to achieve. The very general rule of thumb is
HP = .257 * (intake flow) * 8 It's important to match the intake flow to the intake...a dual-plane manifold takes up about 25% of the intake flow, a tall single-plane maybe 10%.
Second is runner size, and the general rule of thumb is to
use the smallest runner size that will deliver the required flow.
As you work these numbers you find out pretty quickly why the big dollar heads are worth every penny.