Freeing up the exhaust helps slightly, noteworthy gains if you have a California car with a plugged Trap Oxidizer. (The football shaped thing under the turbo.)

If you really want to go crazy with them, you can source a Bosch "M" injection pump and have Myna over in Finland rework it. There are some crazy people making these engines roar, but it's not cheap. The pumps that are stock on engines here in the USA are Bosch "MW" pumps, and not nearly as adjustable.

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-Josh
Testing the cheap Mercedes axiom, one bolt at a time...