Marauder Returnless Fuel System


Well-known member
Jan 6, 2010
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Fuel delivery on a SC'ed engine is essential to avoid detonation. My initial SC'ed fuel delivery system consisted of a single GT fuel pump, 40amp BAP, and stock wiring. I'm making 13lbs of boost and @ WOT my FPDC is about 96%. It's not bad but I felt the need to lower the FPDC and upgrade the wiring at the same time. I used Brian's (Fordnut) delivery system as a template for my design.

This is Fordnut's design:

I made a few changes to his design to make it my own:
-dual FPDM's
-4lbs hobbs switch (WOT trigger)
-dual wiring to each GT pump (not paralleled)
-3 relays (1 for each FPDM and one for the BAP)
-separate 3/8" hard line to the rail (instead of the single 1/2")

I started with the wiring and added a new #8AWG primary wire with a 40AMP inline fuse from the power block to the trunk. It hits a 40AMP relay(triggered by the inertia switch) then runs into a 40amp KB BAP, then out to 2 separate 20AMP fuse holders. A second relay feeds GT pump#1/FPDM#1. The 3rd relay feeds GT pump#2/FPDM#2 (the relay can also be triggered on by a WOT signal). Currently I have the relays all on triggered VIA the inertia switch. The system can easily swap over to 4 different configurations

-Single GT pump/FPDM#1 with a BAP on @ WOT
-Single GT pump/FPDM#1 with a second GT pump on @ WOT
-Dual GT pumps/FPDM#1-#2 full time (no WOT trigger)
-Dual GT pumps/FPDM#1-#2 full time and trigger the BAP @ WOT
The WOT trigger is a 4lb hobbs switch. Here is a shot of the wiring upgrade. The second FPDM and BAP are wired on the back side of the trunk brace out of site from plain site.

Here is the new FPDM wiring harness

Here is a pic of the 3 relays

I kept 12awg wiring through the trunk and down to the fuel pumps. The stock fuel pump wiring was shield and drain so I did the same shielding for the new pair of wires feeding the second GT pump.

All the added wiring is 1/2 wrapped in electrical tape then protected with convolute tubing, finally tywrapped and fastened

The carpet is nice and flat after the wiring upgrade

The next bridge I crossed was increasing the delivery from the tank to the fuel rails. Having a wrecked Marauder in the back yard was a great help. I removed all the stock fuel lines from the tank to the engine compartment. Cleaned them up a little and installed them. The benefits in using these parts were great. They were free, have the correct bends and connections on each end, and will double my fuel capacity to the engine bay

I made good use of the stock rubber insulator's from the donor car

SS band clamps along with the rubber insulators made it easy to mount the new line to the existing 1/2" vapor recovery line

The new hard line is nice and tight on all ends

The front hardline dropped right in. The rear one took a little work to figure out. Once I held my head in the right position it dropped right in.

The stock fuel filter has to be relocated up higher to make room for the second bracket. I had to cut the right side of the donor fuel filter bracket so it would fit within this area.

The combined lines run into the engine bay and plug directly into a modified -8AN Y block. This block makes use of the stock quick connect fittings and parallels my dual fuel lines to the fuel rail.

The SS braided line going to the hat has a OEM connector that I didn't want to cut so I made an adapter that plugs into the braided line and converts it to 3/8" hose barb. I cut the connector off the donor hat and flared it for a hose clamp.

Now the plumbing is done I got started modifying the fuel hat. Here's a pic of the stock hat with a single GT pump

Instead a taking a chance and deflecting the metal (attempting to weld to the fuel pump hanger bracket) I decided to use nylon locking nuts/bolts, and teflon spacers to hold the two together

3/8" teflon spacers were used to get the proper alignment:

I added a PPRV for a total of 2. The PPRV's were kept in line mainly in the event one pump fails to prevent back feeding fuel into a disabled pump. The car will still be 100% drivable in the event I loose 1 of the pumps. The PPRV has a built in check valve and it also has a blow off valve built in.

Now to the fun part! I needed to add a new fuel line and a new pair of wires through the hat without the possibility of a fuel leak, the options are few in this department and was definitely one of the biggest obstacles. Racetronix has a bulk head wiring harness. That's about it!

The problem I had with this harness is the connector has a push on one way clip that holds it in place. You push it tight with a flathead screwdriver and hope for the best. I found a company that makes a true bulkhead fitting that also has provisions for a pair of 12awg wires with -0- chance of a fuel leak.

The wire that passes through the tank cannot be standard off the shelf stuff. Teflon coated PTFE certified wire is the only way to go. This stuff is military grade wire that will not wick when submerged in any grade of gasoline

For the fuel pass through I wanted barbed fittings on each side of the modified hat to accept 5/16" I.D. submersible fuel hose. The bulkhead is a -6AN and the blue fitting on the outside of the hat was special ordered from Australia (I couldn't find a US seller with a -6AN to 5/16" barbed 90* fitting)

Here's the hat completely modified with dual hangers, dual PPRV's, corrugated hose deleted, dual GT pumps, and dual wiring +-/+-

I installed a smaller sock on the pumps to ensure they will ride on the bottom of the basket inside the tank

The modified hat dropped right into the tank no issues at all.

To connect the 90* barbed fitting on the outside of the hat to my homemade fitting for the stock OEM SS hose I used a short piece of submersible fuel hose and put a piece of nylon braid around it to protect it from the elements.

Currently I have the system setup to run the 2 FPDM's and the 2 GT pumps full time. This is more than enough fuel for my current power level. I still wanted to make it easy for upgrades in the future so I plumbed a hobbs switch inside of the pillar pod. The switch is set for 4lbs of boost and I wired the dry contact of my 40amp BAP. I soldered up a manifold for the nylon hose feeding the boost gauge/hobbs switch.

I wrapped the hobbs switch in rubber insulation to prevent it from clacking around in the pillar pod. The N/O contacts on the switch are run behind the lower gauge

Gen1 Aeroforce Interceptor, Auto Meter Boost, Innovate A/F gauge

With 2 GT pumps, dual FPDM's, full wiring upgrade, and a 40amp BAP this design should support any returnless system making up to 700HP/700TQ. I don't see my Marauder ever going past 575HP so I have plenty of room to grow.
I barely crack 90% FPDC @WOT with just the dual FPDM/GT pumps (no BAP) :fy:
Last edited:


4 Doors 4 Life
Mar 21, 2004
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NW Indiana
Dude that is so over-engineered my head is pounding

Next time you run a Hobbs switch, keep it in the engine bay and connect the ground wire for the relay to it. It's much simpler that way, and cleaner


Well-known member
Jan 6, 2010
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Currently my setup is running twin GT pumps with dual FPDM's Zack.
At my power level they provide more than enough fuel @ WOT without the use of the hobbs switch (I installed the switch for future upgrades). The switch is a trigger for my 40amp BAP so its just a dry contact (no need to run a ground).

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