Nick's Garage just dyno tested a 440 using factory HP exhaust manifolds, max wedge manifolds and headers.
Results:
HP manifolds---- 375 horsepower------ torque- 389
Max Wedge------ 410 HP ----------------- torque-446
Headers ---------- 419 HP ----------------- torque-463
The headers (1 7/8" tubes) increased 44 horsepower. Back in the day everybody claimed they only gave you 15 more horses.
All depends on the combination. Those dyno tests can be "rigged" by changing the camshaft. The results also will change a lot depending on the muffler and tailpipes that are used.
He didn't change anything on the engine except the manifolds. Go to Youtube and type in Nick's Garage, he's a Mopar guy too.
Andy's comment is valid... when you have a cam with a bunch of overlap, the power difference between manifolds and headers will be magnified - headers support scavenging and manifolds don't. As soon as I saw the vacuum gauge reading around 11 in-hg with a pretty lumpy idle, I knew you'd see a big difference. It was impressive to see the max wedge manifolds hang with the headers. When running a factory-type stock cam, I've seen engines only pick up 10-15 hp with headers on back-to-back dyno pulls.
