One thing to look at with the aftermarket muffler is if it's a straight through design. Turbo diesel's thrive on having as little back pressure as possible, which is why even the oem mufflers on a w123 turbo diesel are a straight through design. If you put on a chambered aftermarket muffler for a domestic V8, you're effectively bottle necking your engine even more than stock.

I personally prefer straight pipe, as the turbocharger itself does a great job muffling the sound, and the less restriction the better in our case.

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1981 300TD 4 speed manual
Euro bumpers, zender valance and skirts, H&R springs, billy HD's, leveled sls, real AMG Pentas 16x8 et11, vdo boost/egt gauges intergrated into ash tray, eurolights, led 3rd brake light