Why not just get a real bypass pipe from a 49 states car? It's already sized correctly and has the insulation wrap. The loss of insulation on that pipe is costing you dearly in turbo performance and underhood temps. The exhaust design on these engines is already profoundly stupid.

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Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)