What PSI is ideal for a pair of 40's on a 2056 engine?
Brian

I've read 3 psi is optimal

^^^

Pressure needs to be enough to flow fuel to keep the bowl full, without over-powering the floats.

3psi would be just fine.

I did some testing on my 1.8 with Weber rebuilt DCNF's a few years ago with Moprod low pressure pump mounted under the tank,holley low pressure regulator and gauge at engine.
I found this type of regulator won't go much lower than 3 psi,I noted a drop in pressure at revs I guessed this was the distance from pump to tank.
Set pressure at 3.2 psi and at stayed constant @ 3+,increased pressure to 3.4 and it went rich on idle,increased it to 3.5 and it flooded,coughed and stalled.
Some may have different experience but my test proved the needle and seats started to be overcome by pressure @ 3.4 psi,I'am sure this would apply to Dellorto's also.
I feel that's important to choose a pump that doesn't make too much more pressure that you need,my pump makes 6psi which is a good matchup for the holley low pressure regulator.

Interesting. I may dial mine down a tad from 3 (Dellortos).

I don't see any problems with <3 and the pressure reducing at WOT, as long as the engine isn't going lean (indicating the pump isn't keeping up with the flow through the carbs). After all, how much gph are we flowing with these engines? Probably not much. And, of course, unlike fuel injection the delivery pressure is not relevant to the running of the engine as long as the pump can keep the bowls filled and not over-power the float.

For reference I'm running a GM in-tank pump within a Fuelsafe cell, using a Holley 12-804 regulator.

Running mine at 3 . . . for years now.

2.5 is optimum, 3 is on the upper end and a weak needle valve will not hold it. I shoot for 2 PSI dynamic and its typically very safe.