As for the exhaust, you always lose torque when upgrading exhaust pipe sizing.

Not true and not applicable to turbodiesels. You could run the exhaust straight out of the turbo housing and have no decrease in torque. Turbos on diesels and gassers benefit from the lowest backpressure possible. This allows the turbo to spool up as quickly as possible. I am going to test my MB out of pure curiousity. I will drill/tap the exhaust pipe a few feet back from the turbo and put a pressure gauge on it and take it for a ride. I'll just stick a pipe plug in the hole when I am done. I'll let y'all know how it goes. BTW headers and big 3" duals work GREAT on NA diesels like GM 6.2's and IH 6.9/7.3's, increase in torque! RT

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