will using a t3 to t4 adapter flange hurt performance?

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the turbo i have is a t4 turbine housing. now i have looked and looked for a t4 manifold , i have found very few, and the few i found are very expensive. so . i have a t3 tubular header. and i found a t3- t4 adapter flange for cheap

http://cgi.ebay.com/ebaymotors/T3-T...ryZ33742QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

now my question is , if i use an adapter flange will this hurt performance? like topend? or spool up? any input is required jk but it is very much appreciate, im going to continue looking for an affordable t4 manifold. but if i cannot find one i will buy an adapter plate and get a turbonetics t3 cast manifold. ( i really like those )

 

[compression]

if you look at the flange, it looks to have a smooth transition. if i had to guess it may hurt spool a little but help top end? or i dont know input is very much appreciated, need it be good or bad.

 

[2gGSX]

The neck down can be solved by some gasket-matched porting. My biggest issue, personally, with running an adapter plate, is that it introduces another point for an exhaust leak.