rising rate fuel presasure regulator
 

will a stock 420sel gain any horsepower from a rising rate or a higher pressure fuel pressure regulator?

No! The CIS injection will actually deliver less fuel with higher system fuel pressure given no other adjustments are made. Don't ask about other adjustments, if you need it explained you do not know enough to modify your CIS without digging an expensive hole for yourself. (not a personal attack, just the cold facts):o

Fuel delivery isn't holding back power in your 420SEL. Limited ability to breathe (in or out) is probably the biggest detractor. Gross tonnage of the SEL isn't helping either. I'm sure there are a few tweaks that may pick it up a little but would probably add up to barely noticable. The 420SEL was engineered to be a comfortable luxo-liner, not a pavement burning hot-rod. Transforming one into the other is going to take a butt load of re-engineering with ever diminishing returns of dollars v/s hp.

I figured so, but I read about then in a bosch book about CIS and it talked about them, and a buddy of mine had an extra one, and I wasn't sure if was worth it to purchase it from him.