If the manifold split was done properly there should be a blocker plate welded into the inside just behind the added outlet flange. If somebody just added a second outlet, it's eye candy and does little or nothing for the efficiency of the exhaust system.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!