Interesting. So despite the theoretical benefits, all show and no go as suspected.
Then, why do some manufacturers install those exhaust systems on four cylinder cars but then conceal them behind the bumpers? The engineers must have seen some kind of actual benefit for those won't they?
(Pictured current generation Honda Civic)
Also, I suppose that the actual benefits of a true dual exhaust vary whether there is one exhaust manifold (inline engines) or two exhaust manifolds (V or boxer engines).