I understand the benefits and strong points of aluminum over iron heads, but how much better, if any, are the fastburns vs. the Vortecs? And how much room for improvement is there to port both sets of heads?

 

The fast burns are a fair bit better, due to improved combustion chamber design and more flow. Plus they don't need the amount of work the vortec's do to run a high lift cam. There is room for some porting, but not alot, it's been shown that the ports are pretty good already, and the factory valve job is close to perfect. Some pocket work and light porting have taken the vortec's up to 271 cfm on the intake, but if you mess with the combustion chamber shape or valve job you can ruin the heads pretty quickly.
John

 

Thanks. Exactly what I needed.