I have HKS 67mm twin Exhaust (one exhaust for each turbo) from front pipe back currently suited where the std dump line up, not souch concerned woth size more so how it replaces cos i really dont want to replace my beloved exhaust...
would like something more free flowing as upgrading to -5s from R34GTR Turbos on my R32 GTR...
split dump (free flow) vs bell mouth design (turbine/wastegate turbulence)...Im still not sure which direction or if information ive been provided with is valid or not...
your dumps look closer to 70mm than 67mm does the reduction have a further negative effect???