exhaust manifold polishing

[JUNAID786]

a while ago i did a 4 into one header. the smaller diameter pipes gave me good low end torque and the 4 into one design made good top end capability too. i took them off this weekend and had a look at the design. here is what i found. the welds were good on the outside but inside there was a step. this was causing a rough idle and power loss from exhaust gas reversion. i also noticed that the exhaust ports were wider than the holes in the manifold