Building a (Semi) Hidden High Flow Fuel Delivery System Part 2

Wayne Scraba

20 Feb 2020

Click Here to Begin Slideshow Last issue, we covered the heart of our covert fuel delivery system (the Holley HydraMat). This time, let’s dig into the nuts and bolts of the subterfuge – in particular, the gas tank. Here we began with actually picking a tank. For this application (and others), there are a number of different replacement gas tanks out there. As a result, there’s plenty to sort through and to think about. In terms of quality, some are ok, some are junk not even close to being “right” and at least one of them is very nice. That very nice one is a correct appearing tern-plated example from a place called Spectra Premium. Basically, it’s a dead ringer for a stock tank and the writer has used it on more than project (this isn’t the first time we’ve built a stealthy gas tank with hidden pickups, but this is the first using the HydraMat “advantage”). These tanks are made in Canada, but plenty of sources sell them in the USA (good examples include Summit Racing and Rock Auto). With a new Spectra Premium tank in hand, we spent some time determining where and how the big square HydraMat could be installed. It was way too large to fit through the sender hole in the tank and besides, we needed space to access and install the pickup and return plumbing along with an external high flow vent. The solution was to cut an access hole in the top of the tank. To get there, we made a pattern using a Holley 4500 carburetor base gasket as the template. The reason for this is because a carb base gasket is obviously fuel safe and is also easy to find; just about every universal Holley high performance “Trick Kit” includes one. Additionally, the “ID” of the 4500-series baseplate gasket is sufficiently large that one can actually reach inside the tank and adjust the HydraMat, tighten fittings and so on. With the template in hand, we simply cut out a piece of 0.090-inch thick aluminum and drilled a series of mounting holes around the outer edges. Again using the 4500-carb gasket as a template, we cut the top of the gas tank. This time, the hole matched the ID of the gasket. With the access port complete, we turned our attention to the pickup, return and vent fittings. Here they’re mounted high on the forward wall of the tank. We can get away with this because the big billet Holley mechanical pump we’re using can easily pull a prime. It won’t work if your fuel pump needs to be gravity fed. And if you think about it, it’s no different than a stock tank arrangement where a mechanical fuel pump draws fuel out of the top of the tank by way of the sender. In our case, one Earl’s #10 stainless steel bulkhead fitting is used for the pickup while a pair of Earl’s #8 stainless steel bulkhead fittings are used for the return line and the vent line respectively. Installing the bulkheads involved cutting appropriately sized holes with hole saws, adding a set of stainless bulkhead nuts on the inside to affix them and then having them TIG welded (thanks to Kory at Fisher Fab!). In the end, it didn’t take that long to cut up the tank and modify it, but cleaning the filings on the inside seemed like a forever job. We still required a sender for the car. There was nothing wrong with our example; it had been recently replaced. Although there are no photos of it, we cut the pickup tube off and capped the line. The float and sending unit still function as normal. But the location of the sender and in particular the float is what determined the location of the HydraMat. It was mounted offset slightly to the passenger side rear of the gas tank. In order to install the HydraMat, we first taped off the edges of the access port with duct tape (a lot of duct tape!). There are two reasons for this: We didn’t want to slice the HydraMat and we didn’t want to slice up our skin. Basically, an excess of duct tape is cheap health insurance. To install the HydraMat, first roll it into a tube shape and then insert it through the access hole. Unfurl the HydraMat after it is in the tank. In our case, once the HydraMat was more or less in place, we adjusted the location by hand. Our HydraMat is held in place with Holley’s rare earth magnet installation kit. As pointed out in our first segment, it takes a lot of force to move the magnets. As a result, brace yourself! You might be surprised at how tenacious four little magnets can be. Next up, we’ll look at how we plumbed the HydraMat internally, along with setting up a fuel return line and a vent fitting inside the tank. We'll finish looking at the plumbing in our final issue. Meanwhile, you can check out the progress in the accompanying slideshow:

Building a (Semi) Hidden High Flow Fuel Delivery System Part 2 — Click Here to Begin Slideshow Last issue, we covered the heart of our covert fuel delivery system (the Holley HydraMat). This time, let’s dig into the nuts and bolts of the subterfuge – in particular, the gas tank. Here we began with actually picking a tank. For this application (and others), there are a number of different replacement gas tanks out there. As a result, there’s plenty to sort through and to think about. In terms of quality, some are ok, some are junk not even close to being “right” and at least one of them is very nice. That very nice one is a correct appearing tern-plated example from a place called Spectra Premium. Basically, it’s a dead ringer for a stock tank and the writer has used it on more than project (this isn’t the first time we’ve built a stealthy gas tank with hidden pickups, but this is the first using the HydraMat “advantage”). These tanks are made in Canada, but plenty of sources sell them in the USA (good examples include Summit Racing and Rock Auto). With a new Spectra Premium tank in hand, we spent some time determining where and how the big square HydraMat could be installed. It was way too large to fit through the sender hole in the tank and besides, we needed space to access and install the pickup and return plumbing along with an external high flow vent. The solution was to cut an access hole in the top of the tank. To get there, we made a pattern using a Holley 4500 carburetor base gasket as the template. The reason for this is because a carb base gasket is obviously fuel safe and is also easy to find; just about every universal Holley high performance “Trick Kit” includes one. Additionally, the “ID” of the 4500-series baseplate gasket is sufficiently large that one can actually reach inside the tank and adjust the HydraMat, tighten fittings and so on. With the template in hand, we simply cut out a piece of 0.090-inch thick aluminum and drilled a series of mounting holes around the outer edges. Again using the 4500-carb gasket as a template, we cut the top of the gas tank. This time, the hole matched the ID of the gasket. With the access port complete, we turned our attention to the pickup, return and vent fittings. Here they’re mounted high on the forward wall of the tank. We can get away with this because the big billet Holley mechanical pump we’re using can easily pull a prime. It won’t work if your fuel pump needs to be gravity fed. And if you think about it, it’s no different than a stock tank arrangement where a mechanical fuel pump draws fuel out of the top of the tank by way of the sender. In our case, one Earl’s #10 stainless steel bulkhead fitting is used for the pickup while a pair of Earl’s #8 stainless steel bulkhead fittings are used for the return line and the vent line respectively. Installing the bulkheads involved cutting appropriately sized holes with hole saws, adding a set of stainless bulkhead nuts on the inside to affix them and then having them TIG welded (thanks to Kory at Fisher Fab!). In the end, it didn’t take that long to cut up the tank and modify it, but cleaning the filings on the inside seemed like a forever job. We still required a sender for the car. There was nothing wrong with our example; it had been recently replaced. Although there are no photos of it, we cut the pickup tube off and capped the line. The float and sending unit still function as normal. But the location of the sender and in particular the float is what determined the location of the HydraMat. It was mounted offset slightly to the passenger side rear of the gas tank. In order to install the HydraMat, we first taped off the edges of the access port with duct tape (a lot of duct tape!). There are two reasons for this: We didn’t want to slice the HydraMat and we didn’t want to slice up our skin. Basically, an excess of duct tape is cheap health insurance. To install the HydraMat, first roll it into a tube shape and then insert it through the access hole. Unfurl the HydraMat after it is in the tank. In our case, once the HydraMat was more or less in place, we adjusted the location by hand. Our HydraMat is held in place with Holley’s rare earth magnet installation kit. As pointed out in our first segment, it takes a lot of force to move the magnets. As a result, brace yourself! You might be surprised at how tenacious four little magnets can be. Next up, we’ll look at how we plumbed the HydraMat internally, along with setting up a fuel return line and a vent fitting inside the tank. We'll finish looking at the plumbing in our final issue. Meanwhile, you can check out the progress in the accompanying slideshow:

We began with a new Spectra Premium gas tank. These tanks are extremely close to a production line piece and the quality is great. The access hole in the top is obviously not stock!

The size of the access port was actually determined by the size of a Holley 4500 carburetor base gasket. These gaskets are easy to find and obviously fuel safe. Additionally, the access hole must be sufficiently large to install the HydraMat and at the same time, install and tighten the pickup and return lines.

We fabricated the access port cover from a sheet of 0.090-inch thick aluminum sheet. The OD matches the 4500 Holley base gasket.

The back of the tank was modified with three stainless steel bulkhead fittings. As you can see here, there’s a -8AN fitting on the far left. That’s the return line. The next fitting is a -10AN fitting. That’s the fuel feed line. Finally, there’s another -8AN fitting on the far right. That’s the tank vent line.

We used stainless steel fittings from Earl’s for each of the bulkheads. To install them, an appropriately sized holesaw was used to make the opening. The nuts were tightened on the inside and local outfit, Fisher Fab TIG welded everything up.

Before installing the HydraMat, it’s a very good idea to tape up the sharp edges of the tank. We used lot of duct tape, but it’s cheap insurance! Your skin will appreciate it too.

Roll up the HydraMat as shown here and insert through the access port. With a sufficiently large opening it all goes together quickly.

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