Audi Control (fuel) pressure regulator Mod. for 1.8L VW's?

[Caddyman3]

I'm told installing an Audi fuel pressure regulator on VW engines is a common modification. Why do this? What Audi CPR is right mod for a 84 1.8L JH engine? and will this affect fuel economy of the vehicle. This engine is currently in an 83 caddy if that makes a difference.

[ps2375]

I think that mod was done when adding a turbo, as Audi made turbo CIS injected motors. That is the only reason that I know of and have heard of doing this mod for.