There's no secret to doing it. Honestly, most people will cut too deep and punch a hole in the manifold so you will have to TIG weld it back shut if you cut through it.
FYI, You will spend a ton of money on buying grinding and cutting supplies if you do this yourself. You can also try using drill bits to start the process but you will break a few in the process and will need a lot of WD-40.
The cast aluminum will take you hours if not days to get it to the picture above,
That wasn't the final finished product either as it was smoothed and polished up even more by the owner.
FYI, You will spend a ton of money on buying grinding and cutting supplies if you do this yourself. You can also try using drill bits to start the process but you will break a few in the process and will need a lot of WD-40.
The cast aluminum will take you hours if not days to get it to the picture above,
That wasn't the final finished product either as it was smoothed and polished up even more by the owner.