Has anyone deleted the venturi jet pump in the factory 2G GSX fuel pump housing and replaced it with a low-pressure fuel pump? I've been spending entirely too much time calculating flow rates based on hose diameter on: https://www.copely.com/resources/tools/flow-rate-calculator/.

I've talked myself into getting rid of it and running an external fuel pump to transfer fluid across the saddle tank. My concern is that, at idle, the fuel pump will over-pressurize the factory 1/4" return line and create back pressure on the FPR. Second issue is, at full boost, the fuel pump would have to increase pressure to meet the 1-to-1 ratio and put the flow rating outside of what's required for my turbo. Most brushed fuel pumps flow significantly less at higher pressure especially above 80psi.

My E85 tune is in the highlighted box on the fuel pump map, that puts it really close to 500hp. The tuner stated that that I was running out of fuel up top as well, so it adds up. Let me know what you guys have done or if anyone has thought of doing this. I should be installing these parts over the next couple weeks. So I'll keep this thread updated.

So far my list of supplies ordered for the fuel system upgrade has been:
-6AN bungs welded to fuel pump housing
-6AN to 8AN 90 degree adapters
-8AN PTFE hose for feed and return lines.
10 Micron fuel filter (SF-601-010-08-BLK)
AEM 400LPH fuel pump
Aeromotive FPR A1000 FPR
Magnus fuel rail
Walbro GSL395 as a fluid transfer pump from driver's side tank.

Never heard of anyone doing it and personally I think it's kind of overcomplicating the fuel setup. I ran the Walbro 535 with the OEM venturi drilled out a little for more flow and it worked fine, car made 630whp on E85 on that setup.

I tend to do overthink things. The issue isn't during acceleration because there isn't a lot of fuel returning to the tank. It's really at idle when using a larger fuel pump . I've had issues on my spyder when I ran two 340LPH fuel pumps. I couldn't get the base fuel pressure down. Ideally I'd like to mimic the factory solution which decreases pump voltage at low-speed and idle, but all the pump controllers and brushless pumps that come with 2-speed controllers are rather expensive. Some of the brushless pumps even come with a separate outlet for the siphon. But yet again, pretty expensive.

You definitely want a larger return line, -6AN should suffice to keep your AFPR happy in your application. It would be interesting to see if having the transfer pump from the saddle will help with reducing cavitation in the fuel tank. Be sure to have more tank ventilation as you may run into a tank pressurization issue. The saddle tank is a hassle to deal with on higher power levels. On a single A1000, I would probably do -8AN feed to the rail.

Otherwise, depending on your power goals, I would rather modify the pickup assembly by drilling the bypass slightly larger, and then doing a bulkhead -6AN return, or just doing an aftermarket pickup assembly and running a -6AN feed (or -8AN) with anything at or larger than a 255HP in-tank pump to an in-line 255HP pump to -6AN feed to in-line fuel filter with straight inlet/outlet fittings to the fuel rail.

I was over-running the stock pickup assembly on -6AN feed 255HP in-tank / 255HP in-line on the stock return hard line at the firewall with a sleeved -6AN return from the rail around the 770AWHP range on race gas. I then changed to a Full Blown twin pump pickup assembly with side mounted feeds.

Next, I was over-running the stock fuel tank / baffle assembly (cavitation) around the 835AWHP range on race gas with a Full Blown twin 255HP in-tank pumps with side feed outlets on the pickup assembly, on -6AN twin feed / twin 255HP in-line pump with twin fuel filter setup to a single fuel rail (both feed lines going into each side of the rail with a center mounted -6AN return line to AFPR). The bypass was also drilled to help with transfer from the other side of saddle tank. With the twin pumps I had no issues, but with the 4x pumps running full time, I was then over-running the -6AN return resulting in unsteady base fuel pressures at the AFPR, and definitely running out of injector on 1350cc's at 43-55psi base pressures tested.

After this, I changed to a fuel cell with twin top-mounted -6AN feeds (instead of side mounted -- we ran into a flow issue, so we drilled / tapped the pickup assembly for top feed and plugged the old side feed ports), and a -8AN return as I was running twin in-tank pumps to twin in-line pumps on separate -6AN feeds to in-line fuel filters, then to dual fuel rails and 8x injectors). An in-tank to in-line twin pump setup will run at higher base pressures, or higher boost pressures than 90psi. The car was doing 1020AWHP on 48psi boost, so around 90-93psi fuel pressures maxing my single rail with 2200cc injectors on the primary fuel system. Duty cycle datalogs for the injectors were suggesting >100% based on pulswidth. The secondary rail with 1000cc injectors wasn't turned on for that dyno day, but it would have easily gotten much more as the setup was designed for 60-62psi boost which I did run several times in the past, I'm sure I could have gotten a couple hundred more awhp out of the car if I tried.

My setup was way over-complicated because we simply didn't have the pump technology back when I did my setup in 2010.

Nowadays I'd just go fuel cell right away either with a large in-tank electric pump to an in-line pump for power levels below 800AWHP or so. For power levels above that, I would go mechanical with a switched prime pump or have a high flow check valve in the system to keep line pressure easier for cranking/starting. The technology has gone so far for both electrical and mechanical pumps that we have many more options.

Be sure you have GOOD wiring that is large enough gauge for power AND ground wires from battery to the pumps, I saw the biggest gains there. I was running a 4 gauge power from the battery to a 4x 8-gauge distribution block mounted by my pump relays near my fuel cell, to 8-gauge power/ground to each relay and a short length of 12-gauge from the relays to each fuel pump. I did a similar setup using twisted 10-gauge to the in-line pump and that was really nice to work with, here is a link to the wiring I used - https://ebay.io/m/LAgFy2 -- Knukonceptz Karma twisted pair 10-gauge wiring.

I was using Signal Stat 192 5-pin relays to control each two fuel pumps (Relay #1 from battery was used to power Relay #2 primary fuel rail in-tank / in-line pumps, and Relay #3 was the secondary fuel rail in-tank / in-line pumps). Everything worked great for wiring.

This is some great info, definitely didn't think of all of the issues that you described. I also updated my original post as some of it wasn't incorrect.

I do plan on running 8AN from tank to rail and for a return, so I think I'm good there.

I didn't think about the vent, so I'll see if there's a place to drill for it. But I'll test it out first to see if I have any issues. Need to find a way to install a map sensor on the tank to monitor it.

I also didn't think about the cavitation issue, it's like a surge tank. I need a transfer pump that can keep up with how fast I'm emptying the bucket. Luckily the GSL395 is the same size as the GSL392 so I can easily swap them out. I'm only using around 300LPH at full power so the GSL392 can keep up without issue.

I'm dedicated to to keeping this car as streetable as possible so a fuel cell in the trunk is out of the question. I went don't that path with the my spyder.