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When you’re building a serious performer like Project Cobra Jet Challenge, keeping a steady, consistent flow of fuel to the motor is obviously very important. Simply getting the juice from point A to point B is not the only concern here – aside from the complications that can be caused by the significant lateral forces this car will generate, we’re also building the car to run on either pump gas or E85 automatically.
You may recall that the heart of the Factory Five Cobra Jet Challenge is a naturally aspirated 5.0-liter Coyote motor, featuring a 312ci Livernois block, Mahle pistons and host of other good-fast bits and pieces, all of which resulted in 624.9 hp, 462.3 lb-ft of torque the last time it hit the dyno, with peak power coming in at just under 8,000 rpm. It’s a healthy power plant to be sure, so we wanted to be certain that the fuel system would be up to the task.
To allow for our new fuel system, we cut out the factory rear cross-bracing in the Cobra to build a custom fuel tank mount. The car is normally designed around a Fox body Mustang factory tank that mounts from the bottom with straps. We are squaring up the new 3/4-inch tubes to the factory 1/2-inch tubes. The powder coated area normally triangulates from both sides to the rear of the car there. The bottom mount shown here is designed to protect the bottom of the tank that bolts to the frame and fits tightly to the tank itself.
Since the car is being flat bottomed and we needed clearance for the rear diffuser, we’ve mounted an Aero Tech Laboratories 12 gallon fuel cell in the trunk, which is supplemented by a fully optioned out Radium FCST, three AEM E85 pumps, an AEM flex fuel sensor, and an AEM filter. All of it is connected up using Russell hoses and fittings. Here’s how it all went together.
A Fuel Cell For Every Occasion
ATL makes the fuel cell of choice for many professional teams across various motorsport disciplines, including NASCAR Sprint Cup, Formula 1, DTM, and WRC.
We selected ATL’s 12 gallon Sports Cell because it’s a proven work horse. ATL’s design utilizes a hard rubber, seamless bladder that is fully approved to the FIA’s stringent FT3 specification. “The Sports Cell bladder is remarkably strong and demonstrates amazing flexibility and deformability in a crash situation,” says Daivd Dack of Aero Tech Laboratories.
The Sports Cell bladder is remarkably strong and demonstrates amazing flexibility and deformability in a crash situation. -David Dack, Aero Tech Laboratories.
Not only is it durable and safe, it’s also resistant to all common fuels including gasoline, diesel, gasoline / ethanol blends and even 100% ethanol or methanol, making it the perfect choice for our build.
The fill plate or lid of the Sports Cell is offered in standard form with a raised fill neck with a billet cap, roll-over valves under both the vent an the filler and two AN-style outlet fittings. They also offer quick-fill and remote fill options as well.
ATL High Pressure “Black Box” Kit (PN ATL-CFD-600-HP) is designed specially for use with fuel injection systems. It includes a 100 psi fuel pump, 3-door surge tank and the required fittings.
ATL supplied its Black Box for demonstration – a pump-equipped surge tank is mounted within the fuel cell and held in place by the safety foam baffling. These units offer enhanced fuel scavenging, particularly for fuel injected applications, as the trap doors on the collector box swing open under load (like when accelerating or when cornering) and then close to trap the fuel.
As for the internal foam baffling, ATL’s SF103 foam is for use with gasoline and gasoline blends up to E85. For 100% ethanol or methanol, ATL recommends using the SF110 foam. “Keep in mind that no foam is perfect with pure alcohol though. We still recommend checking it often for signs of deterioration and replacing it at any sign of break-down,” Dack cautioned.
A Surge Tank With All the Fixin’s
While we dig ATL’s Black Box surge tank, we wanted to make absolutely sure that the Cobra Jet Challenge wouldn’t run into any fuel starvation issues in the future, so we opted to swap in a Radium FCST. Radium’s fuel cell surge tank is trusted by professional motorsport teams worldwide and their development of the FCST is focused around curtailing the issue.
The FCST is not a glorified trap door box. It is the first of its kind to feature a true dual-chamber fuel tank utilizing a single lift pump and up to three surge tank pumps, all in a compact drop-in package. The 2.2-liter canister supports one, two, or three internally mounted surge tank pumps capable of up to 1,350 lph at 43 psi.
We found a large demand in motorsports to cure fuel starvation issues that result from fuel slosh. Since the inception of Radium Engineering, we have designed various fuel surge tank systems as a remedy. – JP, Radium chief engineer
Like ATL’s Black Box kit, since the FCST integrates the technology that Radium uses in their surge tanks within the fuel cell, it also keeps the plumbing and installation simple. The FCST will drop into all current fuel cells on the market (Fuel Safe, ATL, Pyrotect, Jaz, Harmon, etc.) that use the common 24-bolt, 6×10 fill plate flange. Current fuel cell owners can also reuse some of their existing components like fuel sending unit, vent valve, fill neck and cap.
For our build we were starting from scratch, so we picked up Radium’s fuel cell fill neck and cap (PN 20-0197), roll over vent valve (PN 20-0156), and 6AN Y-adapters (PN 14-0186). We also used premade internal and external wiring harnesses – one for the lift pump and two for the surge tank pumps, as well as their “Green Top” multi-pump fuel pressure regulator (PN 20-0100) and triple valve in-tank collector box (PN 20-0150).
The surge tank is slightly larger than the opening of the fuel tank bladder, so you need to do a little massaging.
Slick Coyote Fuel Rails
From a functional standpoint, the FCST and an external surge tank are identical, but by using the FCST the plumbing required is much simpler, using two fewer hoses (1-lift pump to FST, 2-FST to gas tank). The FCST can be configured with everything needed in order to make a drop-in installation in a fuel cell, with external wiring for fuses and relays being the only additional requirement.
Each of Radium’s Ford Coyote fuel rails uses a 0.69-inch internal bore with -8AN ORB threads. They feature 1/8-inch NPT and 3/8-inch NPT center ports for their fuel pressure gauges, fuel pulse dampers, etc. They also offer a PTFE fuel hose plumbing kit that connects to the OEM feed line.
We also wanted to add the ability to switch between pump gas and E85 more or less on the fly, so we added three E85 pumps, a flex fuel sensor and the requisite filter from AEM Performance Electronics. AEM’s fuel pumps have an internal construction that is specially designed to withstand alcohol contamination, with special attention paid to the armature, commutator and turbine components. Additionally, the end plates of all of AEM pumps are hard anodized, and the pump bodies (flux tubes) of their E85 pumps have an alcohol resistant coating.
And while AEM’s Infinity EFI system will work with any flex fuel sensor, for the sake of simplicity and reliability, it made sense to pick up the sensor from them as well. “We offer a flex fuel sensors because it is usually easier to get as many parts as you can from one source and we can offer them at a competitive price,” says Lawson Mollica of AEM Electronics.
There are a few other advantages as well. “You can get them with either AN or barb style fittings and we include a pigtail, which you might have to purchase separately if you get an OEM style sensor.”
A look at how the AEM pumps and flex fuel sensor integrate with the Radium FCST. The design of the system is very simple - the lift pump fills the surge tank (which automatically overflows back into the tank when full) and the two surge tank pumps serve as the primary means to pump the fuel back to the engine. Also included is Radium's fuel collector box that keeps fuel around the pickup with three check valve balls, which keep fuel from sloshing out around the turns.
Hooking It All Together
Since we’re running two different types of fuel and maintaining consistent pressure was a high priority, we reached out to Russell Performance to get all the plumbing we needed to connect everything up.
The biggest benefit of ProClassic II is the weight savings. It has the same strength and benefits of a regular braided line with integrated mutli-wire, but without the weight of the outer braided material. “We’ve had racers replace all of the lines on their cars with ProClassic II hoses and they’ve been able to remove as much as 18 pounds in weight,” says Eric S. Blakely of Russell Performance and Edelbrock.
Going with the ProClassic II lines and Full Flow hose ends were obvious choices for the Cobra Jet Challenge, not only because of the substantial weight savings but for their durable construction as well, both of which are particularly important considerations for a project that is being built for competition.
When you’re putting together a purpose built car like the Cobra Jet Challenge, small savings like this can start to add up, especially considering that much of the savings to be had at the outer ends of the car rather than in the center.
Fortunately that weight savings doesn’t come at the cost of durability, as the ProClassic II hose features a nylon fiber braided outer cover over a chlorinated polyethylene (CPE) synthetic rubber inner line for abrasion resistance. That CPE inner liner also incorporates a bonded multi-braid stainless wire that allows the line to flex more without running the risk of pinching the line. “It improves the bend radius with less possibility of collapsing when routing hoses in tight areas,” Blakely explained.
What’s more, these hoses are designed to work under some fairly substantial pressures of up to 350 psi and are safe to use with a wide range of fluid types, including oil, antifreeze, and various types of fuel.
As for the hose ends, we went with Russell Full Flow pieces. Not only are these ends reusable, they’re also made from aluminum so they’re light weight as well. The Full Flow ends feature a unique taper design that makes assembly, repair and maintenance quicker and easier, and they also offer 37° angled sealing surface which guarantees a positive anti-leak seal. These ends will also accept a wide variety of lightweight aluminum AN style adapter and carburetor fittings and have the added bonus of being interchangeable with many other manufacturers’ hose ends.
After hooking everything up and making sure everything went together as planned, we installed a shroud inside the trunk to protect of the top of the fuel cell from the outside elements. ATL supplied their fuel level sensor that bolts directly into the Radium FCST. Radium's fuel pressure regulator features an outlet on one side, with two inlets and a return on the other. The two AEM pumps feed the inlets from the top then the return below will feed back to the tank. This means we don't need to run a return line off the engine and the Radium regulator will maintain a static 57 psi of fuel pressure at all times. Once the fuel exits the regulator, it passes through an AEM fuel filter and a bulkhead fitting that channels the fuel up to the engine. Once there, it is split via a Radium Y-block into the back of the fuel rails and the front of the rails are capped with an o-ring plug.
With all of the components of this burly fuel system in place, the Factory Five Cobra Jet Challenge project now has a way to deliver both E85 and pump gas to that 5.0-liter V8 that’s free of potential fuel starvation problems, fits the dimensional constraints of the roadster properly, and is design to withstand the abuses of competition use. What’s more, much like the floating axles, pedal box and front suspension and brake installations on this project, the work was completed in a home garage.
Want to continue watching this project take shape? Be sure to keep up with the Cobra Jet Challenge on the project build thread and the Project FFR Cobra Jet Challenge Car page to see what’s next.
Inside the Radium FCST
- Fully assembled and wired from Radium with one AEM E85 lift pump and two surge tank delivery pumps
- Radium fuel cell fill kit
- Radium roll over vent valve
- Radium In-tank fuel collector box
- ATL fluid level sensor
