Be sure that the EGR is not enabling while you are under acceleration, as that will rob a significant amount of power.

Many people feel that the EGR is useless on a diesel, as the EGR simply restricts combustion, often harming efficiency and power. In a gasoline engine the EGR essentially simulates a smaller displacement, increasing efficiency.

How "free flowing" is your exhaust? Others have noted a significant gains changing from a stock exhaust to a 3" straight-through exhaust.

How bad is the exhaust manifold? Is it at all similar to the 617's?

Besides custom exhaust shops, a motorcycle shop is a good place to get small pipes bent into crazy configurations.

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$60 OM617 Blank Exhaust Flanges
$110 OM606 Blank Exhaust Flanges
No merc at the moment