Why change from OEM you may ask ?, crawl under your truck have a look see, if you have stock and it is free of holes count your blessings, as you are getting full drive energy to the turbo, if not
you ARE losing performance even little holes=lost performance.
Notice the bends, are they smooth or crinkled up in the radius, crinkle = non laminar flow which in itself is a loss but can be lived with for most 6.5s, but hidden from view with a GM style x-over is double walled construction, a few of those double walled X overs have collapsed internally and that can't be lived with.
Visually you can't tell if it's collapsed, a simple test is to run a golf ball thru it if it passes all way then you probably are not restricted in flow, what isn't known is when/if it has collapsed later down the line after passing the "golf ball test", or how would one know if the inner liner let go and cause what Hank has going on in this thread
http://www.thetruckstop.us/forum/showthread.php?t=14852.
Hank is a machinist and can easily tell cast from steel, or other debris material; but it did get me to wondering the "what if" scenario when I 1st saw it.
These GM manifolds are getting some years on em now, how many times can the inner core be exercised hot-cold before cyclic fatigue takes it's toll, so performance gains aside, as a longevity insurance option to turbo health I'd be looking at a new x-over, last production for these was 2000, it's 2010 now 10+ years of thermal cycles if you have the factory one
You see in the attached photo an example of a "good" GM X-over (low miles for sale) if you really want it
I have kept for nostalgia I guess
