I am going to port and polish the inside of my v12 exhaust manifolds, prior to getting them ceramic coated. I want to do this prior to my 6.0 going into my convert. At this point I am going to smooth out all of the rough casting surface and open up the output portion, as it is a tad bit smaller than the actual opening going into the downpipes. The inlets look to be the correct size, the gasket just needs to be opened up a little bit.

Anybody have any previous experience or recommendations. I know Alan Scott's TWR book stated that porting the manifolds produced some sizeable gains, but they ended up cutting them open and welding them back together, and he doesn't go into much detail. I only plan on doing work that I can reach into, I will not be welding any cast iron here.

Thanks!!

 

Extrude honing is the way to go if you ask me. It gets the closest to actually mimicking flow

 

Alan Scott also cut open the intakes, heavily modified motor!
Just match the ports on the head, and your downpipe and you should be good to go!

 

I do porting and can tig weld castings, I might play around with old manifolds and see if I can't them opened up.

I'm going with full sheet metal intakes similar to the ones aj6 came up with but with better shapped plenums.