We recently did a maxed out full port on the Sidewinders ( same head I believe) and the results were right at 313 CFM intake on a Very correct , calibrated, stingy bench.
I am sure as time rolls on and more heads are whittled on that it will get better but honest, this is a street strip head not intended to go toe to toe with Victors, Indys etc
It is designed to be an Edelbrock killer and I guess you need a "Sidewinder" to shoot at Stealths?
So far---I have done several strong street engines with these heads --ZERO issues--I love the casting quality and the seats and guides are some of the best on the market --ports are more equal on these than other brands as well.
We have a regular old 440 flat top headed to the dyno soon with a set and a hyd cam so will report.
I love the quality for the $$ and feel like they are the best answer out there for a street/strip big block--way less than Edelbrocks and IMO better overall quality than everything else.
Want to race hard and go really fast? Sure, there are better choices but these heads will do anything an Edelbrock Performer head can for LESS $$ and at 313 CFM--Surprise many a bracket racer!!
Now...spending the loot it takes to get 313 CFM range--on a street head? Well... that is up to the individual, and a real race head may be better choice but...the heads are VERY capable of some Serious HP!
So far....I LOVE these heads!