Guys, looking to upgrade to a -8 feed with a walboro 455, when does the return line become a restriction? can I run a -8 feed with one or two 455 walboros on a stock return?

 

i would think anywhere thats smaller than the largest section of your system is going to be a restriction. fwiw i ran all an-8 lines into billet rails that look huge compared to oem to an8 return lines. no crossover for the rails did a y prior and ran 2 lines in and out

 

When I designed my fuel system I had the same question. I called magnafuel for advise and for info on the 4303 pump. The guy told me when they see problems with the FPRs is because the return line is to small or restrictive. I used 10an feed split to 8 before rail and return 10an. After reading about so many guys having to redo their fuel systems I figured "go big"

 

Generally the return is only going to be an issue when you've got HIGH fuel flow and the engine isn't using much fuel. I ran into this with a Supra that had 2x 255lph Walbro. When first installed fuel pressure was fine but after a month or three I noticed it was high at idle. Long story short the pumps broke in and out flowed the return at low demand, I was using the stock return. The solution was to stage the second pump as I entered boost, no more whacky fuel pressure issues and it would only go rich a split second as the second pump turned on.
If you're going to be running a new return line it need not be huge. You aren't returning all the fuel back to the tank, just what you don't burn and at idle or just off idle is when you'll be returning the most. I know some don't like it but staged pumps worked well for me on my Supra and with the right protections you can avoid issues if a pump fails while having a high flow system. I'll likely do it on this car too...

 

From experience on multiple cars, a -8 (splitting to 2 x -6 to rails) feed with a single -6 return is more than sufficient for 2 X walbro 450 pumps (that is 1100whp worth of e85 or 1300whp of race gas)