Fp regulator mods

[Mike Pitts]

>--but how (and to what) are you venting the rest of the diaphragm 
>area on the fuel side of it?? 

Ahhh, good question!

This one is easy.  But to understand it, you may need to have a cut 
open Bosch regulator in hand.

On the fuel side, the fuel from the rail forces the diaphram up, which 
opens a puck that seals a pipe which leads to the fuel return line.  

Around this puck is a rather large diameter "slug". If I braze a pipe 
into the bottom half of the regulator of the same diameter as this 
"slug", and at the proper height (critical), the "slug" should act as 
a new seal.  Nothing fancy.  Just a brazed pipe about 0.95" O.D. in 
diameter and 0.80" in height.  This will remove 0.70 sq/in of fuel 
pressure exposed surface from the bottom side of the diaphram.  
This new surface area is approx. 57% of the original area. 

There are other concerns, like, will the slug act as a proper seal? 
This can be easily remedied by micropolishing its surface (2000 
grit paper on glass)

In answer to your question above, the "venting" is to the fuel return 
line, if you can even call it venting.  It's more like a differential of 
pressure between the inside the regulator and the inside of the 
fuel return line.

I do believe this will require a lighter spring -or- a ring of precise 
thickness made to act as a shim to raise the top of the regulator 
since the original spring will now overpower the diaphram and 
cause the base pressure to skyrocket given the reduction of force 
coming from the fuel side of the diaphram. I prefer the ring method 
so I don't have to go hunting down a perfect spring.  Making the 
regulator adjustable will help with fine tuning.

I liked the idea of adding larger or multiple diaphrams, but that's 
too complicated for this home project and frankly, beyond my 
skillset.

Thanks for the input and questions, keep 'em coming!
-Mike
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Mike Pitts
Delray Beach, FL
mpitts at emi.net
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