I just bought a walbro 255. Do I need to upgrade my FPR?

 

No (unless its different for an N/A). I've been running a walbro 255 without a FPR for 3 years.

 

It may be a little different for a NA. The following is from a good article, (link below), by Sean Cathcart, the piece is on adding NOS to a NA FC3S, but this portion points out the difference FPR between Turbo and NA...:

First and foremost, a nitrous inducted engine needs fuel. Every RX-7 running nitrous oxide must first upgrade their pump. The WALBRO drop-in pump is more than apt in this situation. In NA’s, this can, however, present a problem: The stock fuel pressure regulator is unable to compensate for the added flow of a higher volume pump at idle and low load situations. With this upgrade, the stock fuel pressure regulator cannot flow enough fuel out as is coming in, and the fuel rail pressure increases, causing the injectors to add more fuel than the ECU registers. Hence the car runs rich at idle and low load throttle. This can cause hesitation and a large lack of power on the bottom end of the cars, as well as compound a carbonizing problem already existing in the lower rpm range.

Turbo cars already have upgraded pumps, and although they run the same fuel pressure regulator, use a resistor pack to lower voltage to the pump at idle and at low rpm points.

In order for an N/A car to run properly with an upgraded pump, either the Turbo fuel pump resistor pack must be wired in, or an aftermarket, higher flowing fuel pressure regulator must be added. The latter is obviously better for overall tuning, but there is the added cost, not to mention the change in fuel system plumbing. Regardless of method chosen, this problem must be addressed.

From this article/site:

http://www.turborx7.com/nitrous.htm

-Rob