[GThound]

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	~ $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	~ $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	~ $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.

 

[GThound]

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.

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.

 

[DavidF1972]

This is something I will need to do as well... so I'll be watching you very closely... muhahahaha

 

[jayhawkjesse33]

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.

 

[GThound]

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.

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.

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.

 

[GThound]

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

 

[jayhawkjesse33]

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

You can probably buy the low pressure one for less and then buy the better Walboro pump and call it a day. I think the only difference is the pump, if memory serves me (too lazy to look it up!). That unit was so easy to work with and install. I purchased the hole saw off Amazon for less than $20 and it added to my tool collection.

 

[GThound]

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.

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.

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.

here are the two halves together

 

[DavidF1972]

How will it be sealed?? If running a rubber gasket you would need to allow for its thickness.

 

[GThound]

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).

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.

 

[The Scifi Guy]

Or you can save yourself a lot of unnecessary work and install an Edelbrock returnless fuel pump system, as I have done on my present car and the new one I'm building:

Universal EFI Fuel Sump Kit #36031, 35-90 PSI, 67 GPH/255 LPH

Universal EFI Fuel Sump Complete Kit w/pump, tank, lines, mounting kit.

www.edelbrock.com

 

[DavidF1972]

or silicone seal.

If just using a silicone sealant, I would use 3M 5200 it's fuel proof. I would also consider using blind holes for the threaded part. Since the tank is inside the car you don't want to take a chance with fuel wicking up the threads.
Don't mind me, I'm just thinking outloud

 

[jayhawkjesse33]

What your doing is basically what Holley already did. Thick, compressible gasket (up to 1” of surface variance). Find the right part of the tank, which I did and be done with it all.

 

[GThound]

Or you can save yourself a lot of unnecessary work and install an Edelbrock returnless fuel pump system, as I have done on my present car and the new one I'm building

Seems like another good option to add to the matrix, although even pricier at $500.
Very nice engine compartment!

 

[GThound]

View attachment 444191
What your doing is basically what Holley already did. Thick, compressible gasket (up to 1” of surface variance). Find the right part of the tank, which I did and be done with it all.

By the way the ports are pointing, Did you run the fuel lines up the passenger side?

 

[jayhawkjesse33]

By the way the ports are pouring, Did you run the fuel lines up the passenger side?

That was just a test fit.

 

[GThound]

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.

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.

 

[LynnB]

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."

 

[GThound]

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.

 

[LynnB]

Nitrile.