DIY DW400 Lowside Upgrade
 

My ZL1 ran out of lowside volume at around E40, so I decided to investigate retrofit of a DW400 into the stock fuel pump assembly. I purchased a new OEM fuel pump assembly, DW 9-403 pump and 9-1047 installation kit that worked out perfectly.

I went with the DW400 because it flows better than a Walbro 450 at 70 psi on E85, is a close physical fit, draws relatively low current for its flow, has an integrated check valve to retain fuel pressure, and includes a Venturi port for fuel transfer.

The stock pump body is 43mm and the DW is 46, so mild dremel work is required to make the pump fit in the stock assembly. Additionally the stock check valve / filter input feature is removed, but creates a nice feature hold the pump in place. I modified the bottom filter assembly to turn it into a retainer with clearance for the DW filter.

The only question at his point is if the FPCM will throw a code for the additional current draw. This pump will draw 17 - 20A at 13.5V

Great idea, looking forward to seeing how it works out!

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This is great!

Sooo I'm doing a little research and it looks like the ZL1 factory low side flows around 475 lph @ 0 psi. Do you think you will gain much fuel with thsy pump?

I think the more interesting question is: What does the ZL1 low side pump do at say 70 psi?

Unfortunately flow at 0psi isn’t relevant.... it’s flow at 50 - 70 psi that’s important.

The stock pump is likely closer to the Walbro 255 in terms of the volume curve with pressure.

You can get a good sense for what the DW400 might flow at 0 psi if you extrapolate the this flow curve down to 0, but what’s really important is the flow characteristic over pressure.

I think that might be the million dollar question..... I was only able to find data on the lt4 pump at 0 psi.....

Actually nvm.... doing a little more research, I found a flow rating of 300 lph @ 30 psi for the lt4 pump

That’s really good data - thank you. So assuming a flow over pressure curve similar to the DW400 (which might be optimistic for the stock pump considering a 7mm smaller inlet and 3mm outlet on the DW400) the DW flows ~32% more than the stock pump, which is exactly what you need for E85.

You found more data on the stock pump than I did and I appreciate that. Thank you.

Does the higher pressure ratings really matter though? I mean the low side is just supplying fuel to the high side, so as long as there is pressure behind it, it shouldnt change anything. It wont effect spray patterns or anything of that sort, like in a PI motor, if it starts running low at like 40 psi.

Post updates as it comes along.... I think you're onto something... a nice in tank pump would be a good fuel option for those who want to stay below 1000 rwhp or so

In my setup the lowside starts to run out of gas around E37 resulting in a scary fast loss of high side pressure. I lost approximately 1200psi on the high side when the low side was down to around 40 psi.

As a side note - the car is street tuned and this shows up in WOT 3rd gear (M6) but it didn’t show the same issue on the dyno.

Awesome work, you wonder why no one came up with this idea before and there is not a plug and play kit available. Please keep us posted if the pump helps the issue. cheers!