Dyno programs are great directionally, but tend to be off from dyno numbers for any of a million reasons. I like to use the data, and it is really helpful to define the build, rather than determine the result.

The below is based on data from the local SuperFlow 1020 flow bench. Every bench seems a bit different - use the data for direction rather than for absolute comparison. Same situation really - more like a compass than a map. You need both to get anywhere.

Edelbrock's flow data for the unmodified heads is -ahem - "optimistic". The peak number they give is obtainable on our bench but only at a really high lift - well beyond the cam's range. We generally see around middle 250's at .600 lift.

Moderate bowl & detail work and a slightly larger valve will get you into the lower 270s - closer to the advertised numbers @ .600 lift. It takes a pretty nice porting job to hit 300 cfm onn these. We get to the middle 320s with extensive work - but that is cost prohibitive for a build at this level.

Based on my dyno testing - and dynos are like flow benches - the combination listed above will get around 475 horsepower with a 272 cfm head. Assuming a similar flow/horsepower relationship the additional port work could get to around 520ish. The next cam up is the 294S with 248 @ .050 and .605 gross lift - it will get you closer to that 550HP mark. Jay used the even larger 306S cam is his Car Craft article engine to get the "Hollywood" number for the magazine - but that'd cost torque downstairs and idle like a can fulla rocks....