Ed -

Yes, it's large by automotive standards for N/A engines..... but when you add boost, the fuel pressure regulator causes the pump to work harder and draw more current. As you know, with increased current comes voltage drop, depending on wire size and run length.

I see that Jeff Lucius checked the VR4 Denso pump at 15psi boost and found only 10.2-10.5v at the pump. I don't know what size wire is used, but it's probably AWG14. He does say that the run is about 12'. He does not mention testing for current draw, but in the article claims that the Denso pumps can draw more than 16A:

Stealth 316 page

According to tests run by RC Engineering, the Denso pumps also appear to be power hogs. Below is a link to the results of tests run on various pumps at 13.5v and 16.5v. I don't want to use a voltage booster, so I paid close attention to the area around 50psi on the charts, where my pressure will likely be under boost. If you look at the tabs at the bottom of the page, you can select the different pumps tested:

Pump Tests

I'm running a longer route than OE... up the driver side and across the top of the firewall to the relay behind the passenger headlight..... it's ~15' from the pump to the pump relay. If I run 14AWG, the voltage drop is 11.7% to the pump. However, you need to figure the voltage drop of all of the wires in the circuit - battery to relay/relay to the pump. Making it more complicated than perhaps it needs to be is the maximum wire size that will fit in the connector on the MegaSquirt relay board.

Unless I can step up a size in the relay board, I'll run 14AWG from the battery to supply the entire relay board (including the ECU). If I start with ~20A total (estimated) through that wire for 2', voltage drops from 13.6v to 13.4v at the relay board. 14AWG will run from the relay board for a foot or so before it's spliced into a larger wire to make the 15' run to the pump - so that's a loss of another .1v or now down to 13.3v. If I run 14AWG all the way to the pump, voltage will drop to 12.0v on a 15A draw.... certainly adequate. But, if I run 8AWG, the pump should see 13.0v minimum. <img src="/forums/images/graemlins/kewl.gif" alt="" />

Granted, that's not a lot of difference..... and the pump may never draw 15A, but it is a difference - and after my previous experience with the fuel system, I want as much protection as I can reasonably get.

In looking at the OE fuel pump electrical system and knowing the OE fuel pump was tired, I suspect that the entire system was inadequate - old pump, small wiring, restricted fuel flow and high pressure demand under boost causing more current draw causing reduced voltage and less volume = disaster!

I did go to West Marine - and got 8AWG sheathed duplex marine wire.... I know it's overkill (and very expensive).... but I know pump voltage ain't gonna kill the engine.

For splices, I use a metal sleeve (strip them from a standard butt splice)... crimped, soldered and covered with shrink tubing - adhesive filled where possible. <img src="/forums/images/graemlins/kewl.gif" alt="" />

Frank