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Discussion Starter · #1 · (Edited)
I need a high pressure fuel pump to supply the Holley Sniper Throttle Body Injection that I am planning to install on my Opel GT SLANT DRAFT manifold.

I considered just installing a fuel pump near the fuel tank, but have opted for an in-tank fuel pump module with benefits of: 1) runs cooler (hopefully lasts longer), 2) fuel return should be nice and quite, 3) cleaning and refurbishing the tank to prevent fuel pump failure, 4) addition of fuel baffle, 5) adding in-tank fuel filter mat before the fuel pump, 6) clean looking install.

The options I considered were.

Option
Cost
Comments
1. Holley In Tank Fuel Pump 19-350


Camera accessory Camera lens Cameras & optics Gadget Lens
~ $400​
  • Looks really good
  • Pricey!
  • Not sure how well it will conform / seal to tank
  • One of our fellow Opel owners had to replace pump
  • Does not have fuel baffle (see Tanks Inc option with fuel tray)
  • I don't have a 3.25" hole saw (I have a 3" and 4" hole saw)
2. Tanks Inc PA-2
Product Tool Wood Machine Rectangle
~ $225​
  • More affordable, but still expensive
  • Doesn't look as cool as Holley
  • Requires flattening area of tank ridges for good seal
3. Converting Ford F-150 in tank pump for Opel
Automotive lighting Auto part Machine Fashion accessory Aluminium
~ $100+​
  • Cool idea to repurpose OEM part to keep cost low
  • Don't like the look
  • Seal would be questionable
  • I would have to buy a $50 Rivet nut tool to add the threaded retainers inside the tank

After pondering these options, I am leaning towards designing and building my own in tank fuel pump module for the following reasons:
  1. I really want a good seal between the fuel tank and the fuel pump module
  2. I want to maintain tank rigidity, but don't want to weld a panel in my tank
  3. I don't want to spend a lot of money
  4. I could design access hole to use my 4" holesaw
  5. I love to design and build stuff
Let me know if you have other options or thoughts to consider.
 

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Discussion Starter · #2 ·
I am designing a top-plate that matches the corrugations in the top of the Opel GT gas tank. First I will prototype that out of plastic.
Below is the initial CAD drawing. It is circular as the other options listed above, but had the raised ridges to that will fit down inside the opel gas tank corrugations.
Headgear Circle Symmetry Jewellery Fashion accessory
Parallel Rectangle Circle Font Automotive lighting


Once it fits right, I will add some raised areas to drill and tap for the ports.Then, once I land the design comes the fun part, I will cast it out of aluminum!
There will be a circular bolt pattern, like some of the other options, but the bolts will go into a cast split ring that goes inside the tank and has the inverse of the corrugations above.
 

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Discussion Starter · #5 · (Edited)
I almost have the right profile in CAD (after half a dozen test prints) so that the aluminum top piece would fit the corrugations in the top of the tank.. I am a master of getting it wrong the first time, but learn my way there.
Wood Road surface Floor Line Asphalt


I just finished up a little more design work (see pic below on design 1). Hopefully you can see how the corregations on the bottom of the lid, line up with the tank grooves above.


Font Auto part Rectangle Cylinder Automotive exterior


Or I could use a little more aluminum (but I think my crucible should be if enough for the pour) and go for design 2 below. This one is thicker, has internal ports. This design is growing on me, it has the Opel logo on top (hope I got it right) and is a little reminiscent of the Opel gas cap. It might even be easier to cast as it is a similar thickness throughout and might be easier to grip in the vise when drilling the holes for the 1/4” NPT fittings.

Gesture Font Auto part Circle Diagram
 

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Discussion Starter · #6 · (Edited)
The seal between the tank and the pump is outstanding on the Sniper unit, I’ve had zero issues with that. Zero fuel smell, no leaking.
That is good news. Thank you for sharing your experience. It just may sway my decision. I may just end up coughing up the $300 and going with the Holley in tank pump.

[edit] Ooops, just realized that is the low pressure Holley in tank fuel pump. The higher pressure one is $370 + tax, closer to $400
 

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Discussion Starter · #8 · (Edited)
Here is the first half of the 3D print of the fuel module top cap sitting on the gas tank of my Opel GT. Should make for a nice tight seal.
Automotive tire Wood Automotive design Grey Floor


The whole module needs to go back a little further to reach the deepest part of the tank, so I shortened one on the backside runners with the belt sander to match where the tank groove ends. I may need to reprint it this piece before casting.
Grille Automotive lighting Headgear Font Circle


The second half of the model will connect to this half with 3mm stainless steel alignment pins to facilitate keeping the model halves aligned while packing the mold for the sand casting process.

Automotive tire Grey Table Wood Flooring

here are the two halves together
Font Circle Rim Logo Automotive wheel system

Automotive tire Tread Gas Automotive wheel system Wood
 

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Discussion Starter · #10 ·
How will it be sealed?? If running a rubber gasket you would need to allow for its thickness.
Yes, it will be either a rubber gasket or silicone seal. It will be a tight fit, so a thin layer should do it. The key to the good seal (in addition to the seal material itself) is to have clean flat surfaces and even pressure across the interface. Below is an initial design of the bolt-holder that will go inside the tank and receive the mounting bolts. Each hole will be drilled and tapped for 8 mm bolts.I went with 8 bolts (partially because of where they landed).

Yellow Window Circle Fixture Font


I am printing this now and hopefully have a chance to cast it this weekend (although no promises, given our crazy schedule). Then, I will either cut a notch out of it and sort of thread it into the 4" hole in the gas tank, or cut it in half with the bandsaw to be able to get it into the tank. I have yet to remove and refurbish the tank, so that test is a ways out. But, I could at least try casting and drilling and tapping the holes.
 

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Discussion Starter · #17 · (Edited)
Thank you for all the input, thinking, and options. I am going back to a simpler design (a glorified circle), but, still keep the cast corrugations and the 4" access hole using my current hole-saw. I will spend my money where it counts (on $100 on a Walbro fuel pump kit) and build the rest. I'll TIG weld a piece of alumium angle to the underside of the cap to mount the fuel pump and fuel tray. I replaced the 8mm' through-holes in the model with a 8mm tapered cones that should leave a nice mold impression in the sand for casting and act as a drill guide for the bolt holes in the aluminum. I am going to use the same approach on the lower mounting ring (see the cones where bolt holes were), as I could not get a good impression of those sand cylinders when packing up the sand mold last night. The small 3 mm holes are simply for removing the model from the sand and will not show up in the casting.

Slope Parallel Font Circle Symmetry
Slope Font Circle Parallel Diagram


In terms of ins and outs, I am thinking about just a fuel supply out, and a fuel return line. I will likely skip adding an addition vent, as the Opel fuel tank is already vented. I would add the fuel lines by drilling and tapping 2 holes in the inner part of the top cap for 1/4" NPT fuel lines. I will also drill smaller hole for a grommet for the 2 electrical wires to power the fuel pump.
 

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Discussion Starter · #19 · (Edited)
As far as I know, there is no silicone RTV sealant that is impervious to gasoline.

From the data sheet: "3M(TM) Marine Adhesive/Sealant 5200 is not recommended for use as a teak deck seam sealer. Extended exposure to chemicals (teak cleaners, oxalic acid, gasoline, strong solvents and other harsh chemicals) may cause permanent softening of the sealant."
So, what is the best option? Make my own gasket? Rubber? cork? I just ordered a replacement fuel sending unit gasket from Opel GT source and I think it is some sort of cork. I will have to take a closer look. I believe I have a sheets of Various gasket materials from a Felpro gasket kit and could make my own gasket if I know the most fuel impervious material.
 

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Discussion Starter · #24 · (Edited)
Here is the casting cleaned up a bit. It is proof that I need quality better casting sand, more patience, better model building skills, better mold packing technique. Or a combination of the above. The sand was too dry and breaking away at the edges, but I decided to pour the metal anyway. It looks like it could have been a steam/ venting issue. The good news it is oversized so Hopefully I can machine down past the imperfections and at the very least see how it drills and taps

Road surface Wood Automotive wheel system Asphalt Circle
 

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Discussion Starter · #27 · (Edited)
So next steps on this project…I need to decide / identify / source:
  1. Fuel fittings that will thread into the cast aluminum top and Connect to low pressure barb fitting internal and high pressure connection to fuel lines outside. Stainless? I am thinking maybe a street elbow screwed into the top, then, a barbed fitting onto that on the underside of cap to connect to fuel pump outlet
  2. Thread sealer: I am thinking permatex 85420
  3. How to seal flange bolts. I am thinking a nitrile o-ring on each of the 8 mm stainless socket bolts
  4. Nitrile rubber sheet to make the 6” diameter flange gasket
  5. 3D print and Cast the refined new bottom ring (Fun Foundry Day)
  6. Fuel proof electrical seal. Thinking about terminals that pass through plastic/rubber seal or moisture proof electrical seal, or a grommet and some sort of sealer.
  7. Siphon to drain fuel from tank (I am below a 1/4)
  8. Fuel tank sealer (I am thinking POR 15). It have never tried such a product
  9. Make fuel line material decision and procure new supply line. braided nylon? Aluminum hand form line? Stainless steel fuel line?
  10. Fabricate the pump bracket (Fun TIG welding day)
  11. Fabricate fuel tray (dub TIG weld day)
  12. Assemble the in tank fuel pump module
 
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