Hughes must have gotten the “really good” ones from Edelbrock.
The ones I’ve tested were more like 409@.800, on a 4.500 bore.
Exhaust was 240 without a tube and 273 with a 2-1/8” tube.
I would agree the numbers are a little happy! OTB - mine went right around 430 at .800 after being prepped - I have talked with the edelbrock designer on these and he even said much above 440 is the about the outer limits - but I guess with the right hand finish the right flow bench its possible. the hughes exhaust numbers - I would assume they ran those with a tube to get that kind of result - but I don't look at the exhaust side as real world indicator
