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1972 Chevrolet Corvette Scarlett Project Car - EFI Fuel System

In the Tank - Project Scarlett gets a new EFI fuel system

Jeremy D. Clough Jul 1, 2014
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It takes three things to make an engine run: fuel, air, and spark. While we had previously upgraded the fuel system to handle the Zex nitrous oxide system on the original small block, it became clear that our 600-plus-horsepower 416 was going to be a lot thirstier. This meant we needed a comprehensive replacement of the entire fuel system to something more EFI, and horsepower, friendly. As with the rest of the work on Scarlett, “we” consists of Tray Walden, owner of Street Shop, Inc., who has graciously offered his shop and services for the project, and me.

We started by replacing the fuel tank with a stainless one from Rock Valley that we ordered through Street Shop. It came with an Aeromotive A1000 in-tank fuel pump already installed and was significantly larger than the factory tank. Unlike the factory tank, which feeds from the bottom and doomed to leak at some point, the Rock Valley tank inlet and outlet are located on the top of the tank, and the pickup is protected by a swirl-shaped shield to keep it covered with fuel even while cornering.

A perfect storm resulted from the large size of the factory filler and the slightly constricted access to it that resulted from using a Le Mans-style filler. The raised height of the larger tank made it virtually impossible to line the filler up with the opening in the decklid. We could line it all up, but once we start cranking on the straps, the tank would rotate out of place, trapping the fuel cap. Ultimately, Tray welded up a narrower filler neck from a '54 and bolted that into place. Once tightened up, it all lined up perfectly.

Since we're using a FAST XFI computer, that is capable of running the motor on gasoline, LP, compressed natural gas, and E85, we purchased the GM flex fuel sensor required to run the motor in flex mode. Although I'm not dying to run Scarlett on E85, since you never really know what's coming out of the fuel pump anymore, it seemed like cheap insurance.

With everything in place and tight, we hooked up the positive and ground wires to a battery charger and ran the pump, and used the Aeromotive regulator to crank the pressure up to 65 PSI. We then inspected the new system for leaks and tightened where needed. With that, our C3 was one step closer to hitting the road.

Original Fuel Tank 2/23

01. Here’s the original fuel tank along with the steel straps, rubber boot, and drain assembly that went around the stock filler neck. Our Rock Valley tank came with new straps that had to be cut to length and shaped. We also opted to replace the decaying rubber bits with new reproduction pieces.

Factory Tank Rock Valley Tank 3/23

02. You can see that the factory tank is bit different than the new, larger, Rock Valley tank. Made for a fuel-injection equipped car, the Rock Valley tank came with an Aeromotive A1000 in-tank fuel pump already installed, as well as a bung for a return line. While the rest of our fuel system was AN, the bung was 1⁄2-inch pipe thread, requiring an adaptor.

Stock Fuel Gauge Sending Unit 4/23

03. Since part of the Rock Valley tank’s greater size is in added depth, using a stock fuel gauge sending unit wasn’t possible since the gauge would read “empty,” long before the tank actually was. Instead, we had a custom sending unit made that was the correct length for the deeper tank. Unlike the factory float-and-arm arrangement, the sending unit has a captured float design.

90 Degree Hose Ends 5/23

04. Clearance, always a problem with a Vette, was one of our concerns with both the feed and the return lines. To make sure we had enough room between the fuel tank and the body, we used 90-degree hose ends and checked everything with a straightedge prior to assembly.

Cork Gasket 6/23

05. We used the original-style cork gasket for installing the fuel filler neck, and stainless screws. While we started with the fuel filler neck that came off the old tank, only blasted and painted, clearance issues ultimately caused us to replace it with one Tray welded up using a narrower ’54 Corvette filler neck.

Fuel Tank Assembled 7/23

06. Here’s the fuel tank assembled and ready to go in. We made life easier by attaching the lines to the pump before putting the tank in place. That meant we needed to figure out the lengths of two hoses before installation so that we could install the fittings on the other ends. We could have just installed the new ends with the hoses hanging under the car, but, as you’ll see, it’s much easier to install the AN fittings on a bench. We also got the wiring ready to go. The Aeromotive A1000 pump will easily feed our hungry LS engine.

Tank Straps 8/23

07. In addition to setting up the new straps to hold the tank into place, we used a different crossmember that would accommodate the added depth of the larger Rock Valley fuel tank.

Speed Flex Hose 9/23

08. Most of the fittings and the fuel hose itself were provided by Earl’s Performance Plumbing. We used the Speed- Flex hose, which is ethanol-compatible, and black Ano-Tuff fittings to make sure the system would work with whatever fuel we put it in. In the -8 size, the hose came in 33-foot lengths, and we wound up with about 4 feet left over. We wrapped the hose with tape and used a cutoff wheel to get the hose to the right length.

Brass Fitting 10/23

09. The tape was left on until the brass fitting was fully seated. Take care with the braided stainless wrap since it can really tear up your hands.

Push Lock Hoses 11/23

10. The AN-type vise blocks really made this job easier, as did coating the threads with lubricant. If you want to save some money, and some hassle, Earl’s offers a line of push-lock hoses and fittings that work well for fuel lines.

Aeromotive Fuel Filter 12/23

11. Once we routed the “out” fuel line, we fed it into an Aeromotive fuel filter that we mounted to the frame crossmember. The rubber wrapped filter clamps were also sourced from Aeromotive.

Fuel Filter Framerails 13/23

12. From the fuel filter we ran the line along the framerails, over the transmission crossmember, and to the front of the car. We ran the feed line on the passenger side and the return on the driver side, and mounted both, using clamps to attach the hose firmly to the frame. Keeping the hose ends wrapped in tape is a good way to keep them from getting scuffed, as they’re going to have to go through some pretty tight places.

Vintage Air Firewall Plate 14/23

13. Once we got the feed to the front of the car, we split it with a “y” fitting so we could run a separate feed to each of the two fuel rails, eliminating the crossover. As with the frame, we used clamps to keep the fuel line in place. To keep the two lines separate, we used a pair of clamps mounted on one of the screws that passes through the Vintage Air firewall plate.

1972 Chevrolet Corvette Fuel Rails 15/23

14. When the motor was originally built, we used a crossover at the front of the motor to connect the fuel rails. While there’s nothing wrong with this arrangement, we decided to run a separate feed to each of the two rails. Once we had determined where the “y” was going to sit on the firewall, we built the feed lines that would run to the rear of the fuel rails. We used 90-degree hose ends on the fuel rail side of both lines, and a 45-degree for the one mounted to the bottom of the “y” to keep the two fuel lines loosely parallel.

Fuel Line Rear Feed 16/23

15. The rear feed into the fuel lines was easy compared to the front, where we had to route two return lines into the regulator, and mount the regulator somewhere that the bottom-exit return line could go to the flex fuel sending unit located behind the passenger-side fenderwell. While the option shown here, mounted directly to the rail, was appealing, once we put a gauge on the regulator we became concerned about hood clearance.

Mounted Regulator 17/23

16. After trying a few things we figured out we couldn’t mount the regulator directly to the fuel rail, so we formulated another idea. Tray carefully measured the bolt holes for both the throttle body and the factory mounting bracket that came with the regulator and fabricated a bracket that mounted the regulator to the two driver-side screws that hold the throttle body in place. In the final configuration, we mounted the regulator on its bracket just a little forward of the driver-side fuel rail, replacing a short aluminum hardline Tray had fabricated with an über-short length of braided hose between two straight hose ends. This gave us just a bit of flexibility so we could line up the regulator with the return from the other fuel rail and the return going out of the bottom of the regulator headed to the flex fuel sending unit.

Fast Xfi Computer 18/23

17. The FAST XFI computer we’re using has the capability to run the motor on flex fuel, and does so by using an expensive GM flex fuel sending unit. But, we wanted the E85 option, so we purchased the sending unit, the wiring pigtail, and the push-lock-to-AN adapter fittings.

1972 Chevrolet Corvette Inner Fenderwell 19/23

18. We mounted the flex fuel sending unit to the inner fenderwell just behind where the fender-vent attaches. Fortunately, a few of the holes already lined up, so there wasn’t much drilling. After everything was in place and thread-locked, we shortened the protruding screws and painted it black.

Flex Fuel Sending Unit 20/23

19. The plumbing for the flex fuel sending unit was mocked up using hardware we had on hand, and we carefully bent aluminum hardline into the correct shape. Since the inlet and outlet both used push lock fittings, we used adaptors so we could connect them to the AN fittings used in the rest of the system.

Stainless Lines 21/23

20. Here you can see the aluminum lines we used as templates and the finished stainless lines. We could have used the aluminum lines, but we liked the higher safety margin of the stainless lines.

1972 Chevrolet Corvette Stainless Hard Lines 22/23

21. Behold the finished stainless hard lines. The “in” line to the “y” at the top of the flex fuel assembly is the hose that comes down from the regulator mounted at the front of the engine, while the “out” line at the downstream “y” goes straight down the frame rail and returns to the fuel tank.

1972 Chevrolet Corvette Gas 23/23

22. Then it was time for the moment of truth. We put gas in the tank, ran the power and ground wires to a battery charger, and started looking for leaks. When dealing with fuel it’s a great idea to triple check each fitting and connection point, since a leak could ruin your whole day, or worse. vette


Rock Valley Antique Auto Parts
Stillman Valley, IL 61084
Earl's Performance Plumbing
Bowling Green, KY 42101
Lenexa, KS 66214
Street Shop, Inc.
Athens, AL 35611



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