They have there place. I don't believe their recommended power rating at all. They will handle more than that easily, especially if they are used to feed a turbo or 2!QUOTE]
Here is a chart gleaned from a magazine article awhile back in which they used a 300HP 360 Magnum test "mule" to examine dyno results from a variety of cast iron OEM manifolds and several headers. In this particular test, the TTI stepped headers made more HP and torque than any of the others tested.
If you want to read the whole article online click on this link:
http://tinyurl.com/cebd32g
Here is just the chart:
