Are there any differences between Repro and Original Hi-Po exhaust manifolds, especially in the performance area? What can be done to increase the performance of the Repro's and/or originals? Thanks in advance.
I dont think there is a lot of difference, other than price.
All that you could do is gasket match them, or find some shop that could polish the insides by running compound or rouge (sp?) through them, but the increase in performance might be minimal.
The best process is called extrude honing. Check it out here http://www.extrudehone.com/ It is a bit pricey, but is very, very effective at opening and smoothing the inside of just about anything that can take the pressure. Hope this helps.