Editor’s note: This month’s article showcases the unique fuel system our Project Unfair Camaro will need to power a 1,400hp monster while still being street-friendly, serviceable, and reliable. The tank fabrication takes place in John Parsons’ small shop near Orlando, Florida. —Jim Campisano
With Project Unfair, the drivetrain system is being asked to perform in many different ways: street driving, road racing, autocross, standing-mile, and drag racing. Each type has a unique set of requirements for maximum performance and reliability. This month’s article will focus on how to supply the engine with fuel using the latest in fuel delivery components and electronic control systems.
Project Unfair will cover the vast differences in operating environments that are needed in today’s high-horsepower, multi-use, pro-touring type cars—and then some. It will use very little fuel while cruising down the highway and idling but will need a very large amount of fuel when it comes time to make an 8-second quarter-mile pass or 200-plus-mph top-end run. It also needs to be able to perform well at lower fuel levels on a road or autocross course when the fuel sloshes from side to side.
On EFI cars, if the pump ever runs dry, the fuel pressure will fall and the engine will stop running. Under boost, the effects are much worse: Catastrophic engine damage can occur due to a lean condition. Keeping the engine supplied with enough fuel at all times is a must. Standard pump-on-a-stick or other aftermarket designs just won’t do for Unfair, nor will having it break down on the side of the road due to an overheated or vapor-locked fuel pump.
After battling various fuel-related problems over the years, car owners John Parsons and Frank Serafine (owner of Prodigy Customs) turned to VaporWorx, a new company dedicated to solving difficult fuel delivery problems.
Borrowing the technology of today’s supercars, Unfair will be using dual Cadillac CTS-V fuel modules to do the pumping. The fuel module is an integrated fuel pump and surge reservoir. When fuel runs away from the module during hard cornering, the reservoir keeps the pumps submerged in fuel. A series of venturi pumps draw in fuel from the main tank to keep the reservoir full and overflowing with cool fuel. The modules are spring pre-loaded to the bottom of the tank so the venturi pumps can capture all of the available fuel in the main tank.
The supercharged engine in Unfair will also require a method to increase fuel pressure as boost rises. As manifold pressure increases, it pushes against the fuel injector outlet, reducing the amount of fuel coming out of the injector. The more boost from the supercharger, the harder the fuel system has to work to overcome manifold pressure to inject fuel into the intake port. The pressure range from idle to full boost could be more than 30 psi: from negative 14 psi at full engine vacuum to more than positive 16 psi at full boost. It’s a significant problem because the more boost there is, the more fuel the engine needs.
In order to keep the pressure across the injector constant, a rising-rate fuel pressure system is used. This is usually done with a mechanical fuel pressure regulator, but for Unfair a VaporWorx system will be used to control the speed of the fuel pumps and maintain proper fuel pressure.
Using a combination of MAP and fuel pressure data, the electronic systems will change the speed of the fuel pumps to maintain the necessary fuel pressure. This reduces the amount of heat added to the fuel load, increases the fuel pump life, and reduces electrical power demands. During cruise conditions the pumps will need 2-3 amps with an average output voltage of 6V (see sidebar), and they will consume 15-20 amps at an output voltage of 13V at full boogie.
Since the electronic control system does not need a bypass return like mechanical regulators, only a single pressure line from the fuel tank to the engine fuel rail is needed. The two 3/8-inch outputs of the modules will be tied into an AN10 “Y,” and a 5/8-inch fuel line will be routed to the fuel rails. No external filters are needed since the fuel modules have them built in, so the plumbing from the tank to the engine will be a snap.
The tank construction consists of 0.125-inch 5052 aluminum sheet with custom VaporWorx mounting rings to hold the fuel modules. The rings allow the use of the OEM sealing O-rings and cam locks so that repairs and replacement parts are easy to find.
The fuel level sensor wiring will pass through a bung made to house a hermetically sealed bulkhead that encases an 80-psi-rated PTFE covered wire. Standard wire cannot be used since it can wick up the wire and create a leak. John’s own II Much Fabrication tank vent system will provide fuel slosh control, filtered air, and eliminate fuel smell.
Follow along now as John shows how he integrates a custom aluminum fuel tank with VaporWorx parts and GM CTS-V fuel modules.
The fuel control system for Unfair is complicated by the need for the car to have multiple personalities. On one hand it needs to be able to cruise nicely, but when pushed hard, the fuel demands increase dramatically. During cruise the fuel pump may only need to deliver 4-5 gallons/hour @ 42 psi, but when running an eight-second pass, it will need 135 gallons/hour at 70 psi. By using a fuel control system that utilizes pulse width modulation (PWM), Unfair can have the best of best worlds.
Pulse width modulation is a very fast-acting electronic switching mechanism. The pulse is a square wave function where the switch is either on or off. In the on position, full battery voltage is applied to the pump. The switching function time is called the duty cycle. If the switch is turned on for 50 ms, then off for 25 ms, and repeated, the duty cycle is 66 percent [50 ms / (50 ms + 25 ms)]. By switching the fuel pump on and off very quickly, the pump only sees battery voltage when the PWM switch is on. Unlike a rheostat that would reduce voltage and increase amperage/heat, PWM simply reduces the speed of the fuel pump without the heat.
GM uses PWM technology in mass production. The new Camaros, CTS-V Cadillacs, and many others use similar PWM technologies. Why would GM choose to use a more complex fuel delivery system? The answer has two parts. The first is reliability. By slowing down the pump, wear is decreased and the chances of a warranty return are minimized, plus the pump noise is significantly reduced. The other is that the car can also have a dual personality like Unfair. Turn down the fuel pressure and flow during cruise and idle, then increase them to give the fuel injectors greater fuel delivery capability.
However, OEMs integrate the engine PCM and the fuel system control module (FSCM) to make it work. The FSCM is not programmable, so making the needed changes for Unfair would not be possible. That’s where VaporWorx comes in. The VaporWorx kit is a stand-alone system that requires no PCM commands to operate and can be tuned to suit the engine needs. The fuel pressure sensor output can also be monitored using the Stack instruments (Super Chevy, July ’11) to display actual fuel pressure and set alarm limits. This will also allow data logging so that fuel vs. MAP pressures can be compared and engine tuning changed as needed. The average output voltage of the PWM controller can also be monitored. Though not the true voltage, most sensors cannot react fast enough to the PWM signal and hence display an average voltage. This will give a good indication of how close the battery voltage matches the output of the PWM controller.