I am a compulsive modfier of cars, starting back with my dad's '59 Anglia. So when i was up at the used NASCAR place up in NC a year ago, picked up a used VDO fuel pressure gage for a few bucks. Then, ran an AN four line to the gage (no isolater at first), put it in a black autometer cup, mounted in under the dash, passenger side, aimed up at me. But found the fluctuations of the mechanical Carter pump made the needle fluctuate so much it was useless. I ran the fuel off an AN adaptor at the end of my braided SS fuel lines.
So, i got a short AN female/female adaptor, put a 22 gage hypodermic needle (about the size of a large human hair) in it, and filled the adaptor with fuel proof JB weld. Since then it responds very quickly, and without any needle fluctuation . Basically, nice dampening of the needle fluctuations.
For those who cringe about not using a pressure isolater, if i crash, my engine i am sure will die, (mechanical pump), and the only gas that may get into the cockpit is via a 22 gage needle, i doubt more than a thimble at most. If i crash hard enough to tear off my gage, i have lots of things to worry about. An isloater would be appropriate for an electric pump, and larger lines into the car.
Anyway, i think next to fuel level, and
oil pressure, a working in-cockpit fuel pressure gage is the most useful instruement in the car!
I refer to it all the time, when i start the car, especially when it is after a "heat soak", making sure sure the pressure continues to rise, because it it falters at 3 psi, I need to blip the engine immediatly to get some gas to the carb. When my fuel filter is becoming clogged, i can watch my fuel pressure drop down under WOT (wide open throttle), and know it is time for a fuel filter change. When i am idleing in hot traffic, i keep an eye on it to see if my carb is about to boil over.
So an in-cockpit gage is very useful and helpful to me. My Carter runs a steady 7.4 psi pressure, by the way.