Having bought a sports manifold from a place who's name resembles an outside area you'd expect horses to be kept, It became apparent it wasn't well made, leaky welds etc. so we welded up the leaks and thought that was job done. Oh how wrong we were. Yesterday as we again tried to stop the blowing where the rear (N°4) flange meets the head by fitting yet another gasket, but first we decided to take the whole manifold off and check the trueness of the flange alignment. Sure enough both outer flanges where at an angle to each other meaning there was no way it was ever going to seal as there was gaps where both inner flange edges meet the head of about 1.5mm on N°1 & 4. So in the vice it went, one at a time we heated up N° 1 & 4 downpipes and twisted them to get the flange straight and level with each other. After getting them fairly close (less than 0.5mm gap) the offended part was bolted to a spare head using a rachet strap to pull the flanges in as the twisting had made the whole thing too wide to fit on the studs, it was then tightened down to pull it in contact with the head, all round the flanges. The pipes where then heated to red hot to relive any stress from the twisting and hopefully get rid of the last remaining 0.5mm gap.
After it cooled down it was then fitted to the head using the rachet strap to pull the two flanges in , inlet refitted and all tightened down. It's so much quieter now, so quiet that you can now here the diff whine. Deep joy followed by *+°$**§% as the diff will now need to come out. One last thing if you ever have to do this make sure you either remove inlet completely or disconnect the battery because when the two met yer accelerator cable becomes one with itself. resulting is a mad dash to fabricate a replacement cable from the cable in an old Izusu you happen to have lying around.
I've attached the only photo we took unless you want to see the gasket where it was blowing through.