the stock auto wont take too much more power but if your swapping in an ax15 thats another thing altogether. i might worry about the torque limits of the ax15 if you start making more power. as for actually making more power you can get a little more from the stock pump but if you want any real improvements you need to get a bigger IP and turbo. this applies doubly when towing with a manual since the long injection time of a maxed out stock pump pushes your egt's up quite quickly.

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1985 300D om617: 8mm M pump 175cc 5200rpm, holset he221w @ 30psi, large A2W ic, compounds on the way.
KD9AFT
A&P