Why not send you OE manifold off to a local machinist shop and ask them to port and smooth the insides.
Local machine shops are great and normally will do it for a good (cheap) price rather than having a “Walt Disney” tuner charge you for the same process.
Not only that it’s not going to crack, they should support 400bhp easy! ;-)
Lets be honest if you’re a bar mong, are you really going to benefit from a manifold that has probably been made by someone with the brains the size of a monkfish? :doh:
Great - it looks good, but you might as well heat wrap your OE manifold it would last longer and offer similar performance gains. :roll: