(moved from diesel discussion)

I haven't done this myself, am working on one though. The common knowledge here seems to be that the 603 pump should be able to put out enough fuel for around 200hp. The 606 pump depends on whether it is a 606NA or a 606turbo, the 606NA has the same elements as the 603 (5.5mm) where the 606turbo has larger 6mm elements.

Another factor might be the injection rate, which is determined by the profile of the cam in the pump. It is my guess that the 603.97x pump (3.5L) has a higher injection rate than the 603.96x pump (3.0L) due to the need for injecting more fuel in the same time frame, both for the larger dislacement and for the intended lower emissions.

I have not compared the cams in the pumps, would love to but the $$ involved in having them put back together properly is not in my educate the forum budget.

The deciding factor between 606 and 603 pumps might be that the 606 pumps require the electronics of the 606 engine and later cars. If you're using a 603 engine or a car that is pre-606, you're likely going to be using a 603 pump.

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Gone to the dark side

- Jeff