I have reviewed all of @bbirdwell’s excellent threads about fuel pump relay woes and the treasure trove of technical info and schematics. The massive amount of documentation and cataloging is impressive and very helpful. Despite that, I have questions. I am a mechanical engineer and have a bit of wrenching experience but have never had to mess with fuel systems (graduated from Miatas this year, had to fit 2 car seats...).

I plan on running VRP’s dual Walbro 274 pump setup and want to make sure my wiring is up to snuff https://www.vrpspeed.com/product/stgfpu/. I have reviewed the current vs flow diagrams and see that each Walbro pump would (theoretically) max out at 22A apiece, more likely ~15A continuous. So 44A total peak continuous current with more likely ~30A continuous operating. https://aftermarket.tiautomotive.com...Flow-Curve.pdf

1. Is there anything wrong with running a honking big 120A relay and using the stock wiring otherwise for higher current pumps? I read on one of the FB groups (I know, I know...) about someone using a 120A relay such as this, but for stock pumps
2. What is the benefit to running 2 relays in parallel over one with similar capacity such as in bbirdwell’s two 40A relay schematic? Redundancy? More heat rejection? https://mbworld.org/forums/attachmen...954d1496340044

3. Do I just need to stop being lazy and wire each pump individually? Or is that overkill/is factory wiring sufficient? Pull wire from the battery to a distribution block, split to dedicated circuits with their own fuse+40A relay, then pull new wire to each pump individually? Something nice like this? https://on3performance.com/products/...ler-wiring-kit According to a bunch of the charts on here https://circuitblaze.com/automotive-wire-amp-chart I need to pull new wire for this amperage…This would also require me to ask VRP if they can leave the pump power wires out of the connector so I could wire individually…

This post started out as a short DM to bbirdwell with a few questions but as I typed this out, my questions kept growing. Would love some wisdom from the community! Scary for a long time lurker stepping into the light…

 

I just finished replacing the stock fuse holder with a marine-grade fuse holder with 8-gauge wire. It works yet if I were to completely rewire the fuel pump electrical circuit I would modify my plans (yet again!).

I like the idea of direct connection from the battery to a fuse block (100 or 150 amp fuse feeding the fuel pumps' circuit). From the fuse block to the inline fuse, the relays, and the fuel pumps I would use 10-gauge stranded wire doubled up (i.e. power and ground connections are usually one wire each; I would double up each to as to use two wires each). Two each 10-gauge wires twisted and crimped together at each connection. Copper barrel connectors and a *good* crimping tool. I successfully inserted the 8-gauge fuse block into the circuit but in hindsight I think I would do it differently.

My dilemma, 10-gauge wire tends to overheat at any connection and shed insulation; 8-gauge wire is a PITA to route into the circuit. So...two each 10-gauge wires twisted together at the ends and crimped copper connections with shrink tubing over the barrel connectors. This would be my recommendation. I still believe a 120-amp relay is overkill. I just checked my 70-amp relay today and it registered at 43 degrees F above the trunk ambient temperature; actual reading of 148 degrees F. on a 91 degree F afternoon.