So I have a BB Olds 455. I replace the mechanical fuel pump with an electric one (cam was shot). I used a new electric fuel pump that I had on the shelf, Because I have the return line run, I'd like to use it especially being a Big Block in Miami, vapor lock is a concern. I did some searching on here and found many options and it seems the cheapest is a fuel filter with a return. I'm not opposed to that but, would it be any different if I simply put a T in the line before or after the fuel pump?
Your fuel pressure may drop with just a Tee, maybe not. changing the restriction on the return line will vary the fuel pressure also. The fuel filter with return might need it too, but they work well. It's a bit of trial and error but you can get it exactly were you want it. There are special fuel pressure regulators set up for use with return lines.
You want the return line to start as close as you can get to the carburetor. And go all the way back to the tank. The fuel filter with a bypass is a handy way to do it or you could just tap into the fuel line. You can put a restriction, like a carburetor jet into the return so you don't lose too much pressure. The return has 2 functions, one is to get rid of air bubbles and hot fuel before it vapor locks, the other is to allow the fuel to circulate so it doesn't get so hot. The gas you get today is made for fuel injection cars. They don't have to worry about fuel boiling or vapor lock. So, that is why older cars have this problem more than in the past. O ya almost forgot, a return will relieve pressure when the car is stopped so the fuel won't percolate and flood the engine while parked.
I soldered a length of 3/16 brake from my carb inlet pipe (soldered it in to make a T) then ran it back to the inlet side of the pump, where it was also soldered into a T, following the steel supply pipe. I soldered the both pipes together every 6-8-inches to secure it.. Started the engine with a pressure guage connected at the carb, and crimped the pipe slightly with side cutters until I got 3-4 lbs.. Worked like a charm..
when we were talking about his recently on another thread, I looked at a couple of the filters that have the return line fitting (wix 33041) and saw that the return line has about a 1/16" orifice in it. So, that might be about the right size for what you're doing. btw the number for the 3/8" line filter with return is 33040
Regardless of how you create it, a fixed orifice is only going to give you the pressure you want at one particular engine speed and throttle opening (load) when using a constant speed electric pump. Why not do the job right by placing a non bleed off filter upstream of the regulator and then use a regulator designed for a return line. That way you get a constant pressure at any engine speed or load within the pumping capacity of the electric pump.
Need to ask, where do you find the specs on these filters? i'm trying to find the part #'s that have the orifice in the return and the one's that don't. Wanting to experiment with both to see which works best.
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