Ive watched the video closely and IMO they reported 400bhp seems very high for that level of manifold pressure, they admitted that the head didnt flow that well, this would have held it back. Bear in mind the barra turbo is around this power level and around that manifold pressure. It has a lot more tech than a slant. I have watched quite a few of these guys work and feel the numbers they give are inflated, they never use an air filter or a silencer, rarely drive a water pump, the test are in seconds only. As to what they did to the engine, thats great, anybody could do it. IN my Ford I run up to about 15psi (100kpa) manifold pressure, the cylinder head on my engine is considerably better than the slant, I run lpg so I can run 9;1, but IMO I think Im getting about 200kw and 500n/m which is a way short of what they are telling us. I would say they are getting about the same from the slant. Some of the NA hemi sixes get that power level.