Fuel tank in a 1969 Chevy Nova
Image/Wayne Scraba

In Part 1 of Hidden Assets, we covered the design and installation basics of Holley’s HydraMat fuel pickup system. Now I’ll show you how I installed one in the gas tank of my big block-powered 1969 Nova. It isn’t a hard process, but it does require some planning and patience. Let’s get to it.

The Tank

The process began with selecting a new gas tank. I chose a steel tank that is a dead ringer for a production line tank. Summit Racing offers one from Auto Metal Direct that is virtually identical to mine. The gameplan here was to build a fuel delivery system that wasn’t visible on the outside of the car. This isn’t my first rodeo at building a tank with hidden pickups, but it was definitely my first attempt using a HydraMat as the basis for the fuel system.

I spent quite a bit of time determining how to get the big 15 x 15 inch square HydraMat in the tank. It was clearly much too large to fit through the sender hole in the tank–my forearm won’t even. Besides, I needed plenty of room to access and install the pickup and return plumbing along with an external high flow vent.

My solution was pretty simple: cut an access hole in the top of the tank and seal it with piece of metal and a fuel-safe gasket of some sort. I used a baseplate gasket for a Holley 4500 Series Dominator carburetor to do this. The inside dimension is sufficiently large that I can reach inside the tank to hook up the fittings, center the HydraMat, etc. I used the gasket as a template to cut a hole in the top of the gas tank and to make a cover plate out of 0.090-inch thick aluminum. I drilled a series of mounting holes around the outer edges for mounting screws.

Tank Fittings

I mounted the fittings for the pickup, pump return line, and vent near the top of the tank on the forward wall. It’s possible to do this because the external fuel pump I used (a Weldon A600 from Summit Racing) is designed to pull a prime. It’s no different than a stock tank arrangement where a mechanical fuel pump draws fuel out of the top of the tank from the pickup in the sender assembly. The idea won’t work if your fuel pump needs to be gravity fed.

I used a -10AN stainless steel bulkhead fitting for the feed line and -8 AN stainless fittings for the return and vent lines. Installation consisted of cutting appropriately sized holes with hole saws, adding a set of stainless bulkhead nuts on the inside to retain the fittings, and then TIG welding the bulkheads to the outside body of the tank. Cutting and modifying the tank for the bulkheads and the access panel didn’t take that long. On the other hand, cleaning the filings out of the inside of the tank was pure drudgery.

Some may question the need for a vent line, but I use one. A stock system which doesn’t move huge volumes of fuel relies on a tiny hole in the gas cap for venting. Novas and other cars with low-mounted filler necks and vented gas caps are notorious for spewing gas out the back when you get on the throttle. By using a separate high-capacity vent and a non-vented gas cap, my car doesn’t gush raw gas out the back on acceleration.

Installing the HydraMat

The HydraMat replaces the sending unit assembly as a fuel pickup, but I needed the sender to activate the fuel gauge. I modified it by cutting off the original fuel pickup tube from the sender assembly and capping the line. The float and sending unit still function as normal so the gas gauge works.

If you try this for your tank, keep the location of the sender and the float in mind when figuring out where to place the HydraMat. Given the float location, I mounted mine slightly offset to the passenger side rear of the gas tank. This ensures the sender float doesn’t get tangled up with the fuel pickup line at the top of the HydraMat.

Installing the HydraMat inside the tank was next. I rolled it into a tube shape and carefully inserted through the access hole in the top of the gas tank. I taped off the edges of the with a lot of duct tape so the relatively sharp edges of the opening wouldn’t slice the HydraMat—or my arm. You can unfurl the HydraMat once it’s in the tank and adjust the location by hand.

As mentioned in Part 1, the HydraMat is held in place with rare earth magnets on each corner. I chose to install the magnets before it was installed inside the tank. I think it’s easier than installing them after it’s inside–you might be surprised at how tenacious four little magnets can be. I did use a big wooden dowel to slowly coax the HydraMat into place.

Fuel Line Plumbing

My setup requires two fuel lines inside the tank–one for the fuel pickup and one for the fuel return. You must use fuel-safe hose for both of them.

My HydraMat has a large 1/2-inch NPT fitting (most are smaller). The feed line runs from that to the -10 AN bulkhead fitting. That required a length of 5/8-inch diameter hose. There aren’t a lot of options for hose that size that can live submersed in gasoline, so I used Tygon tubing. It’s a yellowish flexible plastic hose that is compatible with most fuels, including those that contain alcohol.

(EDITORS NOTE: Summit Racing offers Pacific Coast Engineering (PPE) submersible fuel hose in 5/8-inch diameter that will work for carbureted applications).

The return line was made using 1/2-inch Tygon tubing. I directed the return line away from the fuel pickup point. It’s also a good idea to keep it submerged in fuel if possible. If it’s left wide open, the spray raises havoc with the gas in the tank, basically aerating the fuel supply.

I used Earl’s Performance Super Stock Hose Ends for the pickup and return lines. They have a barb end that is pushed into the hose. I secured the hose to the fittings with a pair of stainless steel hose clamps on each end. Here are the fittings I used:

• Pickup Line: 90-degree -10 AN fitting with 1/2-inch to -10 AN adapter at the HydraMat outlet, -10 AN straight fitting at the bulkhead

• Return Line: straight -8 AN fitting at the bulkhead

The supply (feed) line from the tank to the Weldon electric fuel pump is -10 AN stainless braided hose. The return line from the pressure regulator is -8 AN hose. Because the HydraMat acts as a prefilter (before the pump), you only need a fuel filter after the pump. I used a big Holley HP Billet Fuel Filter.

With all of the lines inside the tank installed and double-checked, I put the top inspection plate on the tank. This setup requires a non-vented cap that fits very tightly on the filler neck. You might have to try a couple of different caps before you find one that fits properly.

Once complete, the system is all but invisible from the outside. Does it work? As mentioned in that first article, Heck ya! Fuel pressure is absolutely stable throughout the RPM range. It doesn’t spew gas out the back and it’s possible to run the car hard with a quarter-tank of fuel or less. Check out the accompanying photos to see how I did it.

1969 Nova gas tank
Here’s snake’s eye view of the fuel tank on my Nova. No visible sump. No visible lines. No visible pump or filters. And it flat-out works. (Image.Wayne Scraba)
Fuel tank cut to fit Holley Hydramat
I started the project with a new tank. The hole I sliced in the tank top is what I use to install the HydraMat and associated plumbing. It had to be sufficiently large so that both the HydraMat and my arm could fit inside the tank. It also had to be fuel safe and easy to get. A base gasket for a Holley 4500 Dominator carburetor worked perfectly. (Image/Wayne Scraba)
Gas tank hole cover and gasket
I used a sheet of 0.090-inch thick aluminum sheet to make the access cover. The outside diameter matches the Holley base gasket. (Image/Wayne Scraba)
Gas tank with Earl's Performance bulkhead fittings
Here you can see the three Earl’s Performance stainless steel bulkhead fittings I installed on the top wall of the gas tank. The -8 AN fitting on the far left is for the return line. The next one is a -10AN fitting for the fuel pickup line. The -8 AN fitting on the far right is for the tank vent line. (Image/Wayne Scraba)
Duct tape around hole in gas tank
I duct taped the sharp edges around the access hole before I installed the HydraMat. The shields both the HydraMat and my arm from cuts. (Image/Wayne Scraba)
Installing Holley Hydramat in a gas tank
In order install the HydraMat, simply roll it up and insert into the access port. I added the rare earth magnets that hold it in place in the tank. I think it’s easier than installing them with the mat in the tank. (Image/Wayne Scraba)
Fuel sender in a gas tank
The modified OEM fuel sender was temporarily installed. This allowed me to position the HydraMat inside the tank. The idea here is to install the mat so that the fittings clear the sending unit float. (Image/Wayne Scraba)
Fuel pickup line
I made the fuel pickup line from a 5/8-inch diameter, fully submersible Tygon plastic tube with
-10 AN Earl’s Super Stock fittings. The hose was secured to the tubing with double stainless steel hose clamps on each end. The -8 AN return line uses 1/2-inch tubing and one Super Stock fitting. The line simply lays on the tank floor. (Image/Wayne Scraba)
Access hole cover on gas tank
With the HydraMat and feed/return lines in place, I screwed down the home brewed access port cover. You won’t see it once the tank is in the car. (Image/Wayne Scraba)
Fuel sending unit installed
The modified sending unit was installed next. You can see the delivery port is blocked off. It’s also plugged internally. (Image/Wayne Scraba)
Gas tank vent line
The vent line routes to this fitting on the inner side of the driver rear subframe I fabbed a little L-bracket for vent line. You can’t see it but there’s a billet breather topping the fitting at the bracket. (Image/Wayne Scraba)
Weldon A600 electric fuel pump
The fuel pump is a Weldon A600. The self-priming pump is rated at 70 GPH of fuel flow and 100 PSI of fuel pressure. The feed line from the tank is -10 AN stainless braided hose and fittings. The return line from the fuel pressure regulator is -8 AN stainless hose. Because the HydraMat acts as a prefilter, I didn’t have to plumb a filter before the pump. I did plumb a big Holley HP Series billet filter further downstream after the pump. I was forced to loop the line around as shown because of the minimum bend radius for the -10 AN hose. (Image/Wayne Scraba)
Author: Wayne Scraba

Wayne Scraba is a diehard car guy and regular contributor to OnAllCylinders. He’s owned his own speed shop, built race cars, street rods, and custom motorcycles, and restored muscle cars. He’s authored five how-to books and written over 4,500 tech articles that have appeared in sixty different high performance automotive, motorcycle and aviation magazines worldwide.