Maybe the old Vette exhaust manifolds were, I seem to recall that they were larger then the stock type rams horn manifolds on the rest of the cars. Maybe somebody here remembers what years or a more specific application?????? As far as which would perform better, depends a lot on what all is done to your engine. If your looking for any kind of significant gain over the stock manifolds then it would seem modifying the front tube on a set of long headers would be the way to go. I've seen the horsepower claims on shorty headers somewhere, maybe on one of the header companies sites?????