Tech with Jeff: How to Build a RestoMod Fuel Delivery System

Here’s the challenge: design a fuel delivery system that can feed gasoline to an 800 hp engine using an in-tank pump that is stealthy quiet and does not require a return line back to the tank.

But hold off before you break out the catalogs, pen, and paper. You don’t need to design it because the work’s been done for you – mostly by the new car companies! Think about it, automakers are building cars with 500-775 hp they must feed with sufficient fuel – by a system capable of 100,000 miles worth of durability.

This is Carl Casanova’s ’68 Camaro which has run in three One Lap of America events in the last five years, as well as being his fun-run cruiser. One Lap is a 3,700-mile, 7-day, 9-track cross-country competition through 12 states that emphasizes reliability. This kind of torture is why Carl created the VaporWorx system.

When Carl Casanova first decided to convert his 1968 Camaro into a road-worthy, supercharged, Pro Touring car with big power, one of the demands for his car was a rock-solid fuel delivery system.

He investigated how the OE’s were doing it, and quickly realized their returnless system was the best way to approach the problem. Even today, most aftermarket companies shy away from returnless systems. Instead, most recommend building a full-return system, because the return-style mechanical-pressure regulator is easier to control.

There’s nothing overtly wrong with a return style system, but one drawback to consider is that fuel pulls heat from the intake manifold fuel rails and delivers heated fuel to the fuel tank. This eventually raises the overall fuel temperature in the tank, especially at lower fuel levels.

According to Carl, most electric fuel pumps are only about 33-percent efficient, so anything that can be done to reduce heat means less fuel temperature increase and greater efficiency.

Plus, all aftermarket return systems require some type of reservoir or specific pickup system.

For example, the popular “pump on a stick” systems work well, but exhibit a weakness linked directly to the fuel level in the tank. First, as the fuel level drops, the pump must work harder to draw fuel into it. The second weakness comes from fuel slosh while cornering or accelerating, as it can uncover the pump inlet even under mild performance conditions. Holley’s Hydramat helps these situations, since it rests on the tank floor, but still does not cure low inlet head problems at low fuel level.

Fuel pumps are great at pushing, but less efficient at “pulling” or drawing fuel into the pump. Any design that improves inlet flow is advantageous. Ideally, the pickup to the fuel system will always be immersed in a standing level of fuel much higher than the pump inlet. This is one aspect of fuel delivery that is generally overlooked, yet absolutely critical to efficient fuel-pump performance.

The OE’s quickly determined that return systems added too much heat with higher emissions due to evaporation. The extra fuel line and connections also potentially added to both emissions and complexity to the fuel system.

Returnless systems are simpler and less expensive to build but demand a more complex fuel-pressure-management system. The better way to regulate fuel pressure is by managing pump speed through a process called pulse width modulation (PWM). In a traditional fuel-delivery system, the electric fuel pump runs continuously at maximum output. This works – unless the engine demands a very large pump to feed an 800 or 1,000 hp engine that must also run for long periods of time on hot days.

The main issue with continuously running a high output pump is that for a majority of the time, street engines operate at part throttle.

A typical, high-output fuel-injected engine might sip fuel at five percent of the total volume required at wide-open-throttle (WOT). That means that a pump running at full capacity will return 95-plus percent of the fuel at part throttle. That creates wasted effort and tends to over-heat the fuel.

The first thought would be –  just feed less voltage to the pump and slow it down. Unfortunately, that doesn’t work, as all automotive fuel pumps are designed to run at 13.5 volts. Operate one at 6.5 volts and it will quickly overheat — and likely fail — but there is a solution. Pulse width modulation can accomplish the goal of running a pump at low output without damaging the motor.

The engine in Carl’s Camaro is a worked-over LS6 that makes around 650 hp to the flywheel using a 1.9L Magnuson supercharger. This requires not only a muscular fuel-delivery system, but the module must also match the fuel pressure to the boost curve. The Camaro uses the CTS-V pump.

Here’s how it works

Imagine you are riding a bicycle on a level-grade bike path.

To maintain a constant steady speed, you can pedal constantly with very light effort. Or, you can pedal slightly harder, but only for half the normal revolutions, and still maintain the required constant speed. So let’s say for every 10 seconds of ride time, you only pedal for half the time – or 5 seconds. That would be a duty cycle of 50 percent. A PWM-controlled fuel pump can operate the same way. When demand is low, the pump’s electronic controller will feed 13.5 volts to the pump in pulses for half of a given amount of time.

On a voltmeter, this would read 6.75 volts, but the meter is really averaging the voltage reading.

This oscilloscope image illustrates how PWM works. The vertical pillars represent a square wave voltage signal of 13.9 volts. The horizontal scale is time in seconds. Note that the vertical elements represent one-third (33 percent) of the total time, which means the pump is being energized at a duty cycle of only 33 percent. This creates a mean voltage of slightly over 4.5 volts.

The real message to the pump can be seen on an oscilloscope where 13.5 volts is applied for a short pulse then dropped to zero and then a 13.5-volt pulse is applied again. This kind of voltage control is not harmful to the pump, because the armature is likely still spinning when the PWM signal is re-applied.

PWM control eliminates the need for a traditional external fuel-pressure regulator (there is, however, a pressure regulator built into late model fuel modules to prevent over-pressure), but does require a sensitive fuel-pressure sensor. This sensor is matched with a device that can generate a PWM signal that is commanded by the fuel-pressure in the system.

This might look like some kind of essential component out of the Millennium Falcon, but the reality is far more practical. This is a late-model, Gen5 ZL1 Camaro fuel pump module and is the heart of the VaporWorx fuel delivery system.

This is how the OE’s control fuel in modern high-power cars and that’s what Carl decided to create for the fuel system he calls VaporWorx.

Parts List

Description GM PN AC Delco PN Source Price
LS3 Camaro pump module 19208719 M100080 RockAuto $126.79
ZL1 Camaro pump module 19260557 MU2101 RockAuto $196.79
CTS-V pump module 19207950 M10235 RockAuto $345.89
VaporWorx control kit, Camaro    N.A. PWZL13B-23IT Vaporworx $429.00
RetroWorx tank adapter panel    N.A. RWTAK Vaporworx $199.00
VaporWorx QD adpt. to -6AN    N.A. FPOFGMQCAN6 VaporWorx $13.49
VaporWorx Fuel Mod. plug kit    N.A. FMPLUGKIT VaporWorx $13.00


He quickly learned that GM, for example, makes an extremely well-designed fuel module that contains the fuel pump – negating the need for any kind of internal tank baffling or sump.

Next, he needed a fuel-pressure sensor, something that GM has built for years. The last piece required for his VaporWorx kit was a stand-alone controller that would take fuel-pressure readings from the sensor and feed high-power commands to the fuel module.

These are the two VaporWorx PWM controllers. In the upper left is the standard single-pump version with the twin-pump controller in the foreground. Note the placement of the small potentiometer in the upper left-hand position of the twin-pump controller. Once the system is installed, all you do is set the idle fuel pressure with this adjustment and the controller handles the rest. The single controller operates exactly the same way.

This demanded the only major non-OE component, a PWM controller that Carl had designed by a wizard electronics expert. Now, with 7 years of durability testing of his own, along with hundreds of kits sold, the system works.

Besides the PWM controller, the heart of any fuel delivery system is the fuel module. Carl specifies three different GM modules for nearly any requirement from very low horsepower (Carl has plumbed a VaporWorx system into a four-cylinder MG with aftermarket EFI using a Gen5 V6 pump) all the way up to over 1,000 hp.

The included chart indicates which of these GM pumps is recommended based on your horsepower requirements.

OE Fuel Pump Recommendations

HP Rating Fuel Pressure GM Pump
Normally Aspirated
Under 600 HP 60 psi LS3 Camaro
Under 775 HP 60 psi ZL1 Camaro
Under 950 HP 60 psi CTS-V
Under 650 HP 60 psi ZL1 Camaro
Under 810 HP 60 psi CTS-V
Over 810 HP 60 psi Custom twin modules and/or DW300 pumps.


The beauty of this system is that the pump(s) are contained within the module body and are always fully immersed in fuel even when the fuel level is near empty.

How the module accomplishes this is both innovative and incredibly simple.

Let’s say we load a module into a new, dry fuel tank. As you can see from the photos, these modules are designed to operate within a height of 5.5 to 7-inches in height and are spring loaded, which ensures the module seats firmly on the fuel tank floor. Adding a couple of gallons of fuel to the tank and a small, one-way foot valve, allows fuel to enter the module reservoir.

This is a Rick’s stainless-steel tank with a recessed mounting position that allows the tank to sit flush with the floor. The fuel-pressure sensor is also mounted in a T-fitting directly off the outlet. Note also the standard cam-locking ring that seals the top of the module to the tank. These rings are standardized by the OEM’s.

Once the pump is energized and begins making pressure, a small amount of high-pressure fuel is internally bypassed and used like a siphon pump to fill the reservoir from the fuel in the tank. Even with a very low liquid level, this jet-pump assembly pulls fuel from the tank and fills the reservoir to overflowing, ensuring the pump inlet is always covered as if the fuel tank was full. This also maintains a vertical load of fuel over the pump inlet which improves pump efficiency and minimizes cavitation.

One of the best ways to ensure reliability with any fuel-delivery system is to use the highest-quality fuel line available. Carl recommends using a PTFE line. Yes, it’s more expensive, but this material offers the best resistance against failure due to exposure from heat and pump fuels that can affect reliability. There are several companies offering PTFE fuel line such as Earl’s, Aeroquip, TechA/FX and others.

The module also uses a mounting ring which is standardized throughout GM, Ford, and Chrysler fuel modules. This mounting ring locates the module in the tank, which is then locked into place using a standardized OEM cam-locking ring.

Carl recently designed his own 3/8-inch, quick-disconnect adapter that screws together on the fuel output line on the GM and Ford pump modules. This is a foolproof design that will not leak and doesn’t require a special tool to disassemble it.

There are several companies that make fuel tanks for popular performance cars like the first and second-generation Camaros and other cars that will accommodate these fuel modules, making it very easy to convert to a VaporWorx system.

The above description applies to all the fuel modules except the 2009-14 CTS-V, which uses a twin-pump design which increases its capacity. This module was intended to feed the supercharged 6.2L CTS-V engine, rated very conservatively at 556 hp. It is designed so that both pumps run simultaneously. Though it has the highest-flow rating of any GM fuel module, with PWM control its service life is extremely long.

If a stock CTS-V module does not offer enough capacity, Carl can adapt these high-output Deatschwerks DW300C pumps, but they do pull much more amperage. This is important, because the electrical system must be able to deliver adequate amperage and voltage to supply the rated output.

Gen5 and Gen6 ZL1 Fuel Module Performance Data

Performed by RC Engineering in Torrance, CA

PSIG Amps Lbs/Hr Gal/Hr. Ltr/Hr CC/Min BHP at 0.5 BSFC BHP at 0.6 BSFC
45 14.9 463 77.2 292 4869 926 772
50 15.3 436 72.7 275 4585 872 727
60 16 391 65.2 247 4111 782 652
65 16.4 368 61.3 232 3870 736 613
70 16.8 344 57.3 217 3617 688 573

PSIG – gauge pressure

Amps – amperage required to run the pump

Lbs/hr – pounds-per-hour of fuel delivered by the pump

Gal/Hr – gallons of gasoline per hour

Ltr/Hr – liters of gasoline per hour

CC/Min – cubic centimeters of gasoline delivered per minute

BSFC – Brake Specific Fuel Consumption. This is the amount of fuel, in pounds, required to produce one horsepower for one hour. Naturally aspirated engines = (0.5lbs/hp)/hr, Supercharged up to 800hp typically (0.6lbs/hp)/hr.

BHP at 0.5 BSFC – brake-horsepower potential at a brake-specific fuel consumption of 0.5

BHP at 0.6 BSFC – brake-horsepower potential at a brake-specific fuel consumption of 0.6 used for supercharged engines


For even a daily-driven performance street car, this pump module would last near a lifetime of driving. Carl says this OE pump will easily feed up to 75-supercharged-horsepower on gasoline. Above that level, the OE pumps could be upgraded or a custom twin-module system could be created.

The only other major component you would need, besides the fuel module and the VaporWorx electronic-control system, would be a fuel tank. Most ‘60s -‘70s muscle car tanks are usually not quite deep enough to accommodate the fuel-pump module height requirement, which starts at roughly 6.5- inches.

This is a Rock Valley (my bad on the name) stainless steel tank for a C1 Corvette using a Ford fuel module and controlled by a VaporWorx PWM system. The module requires a minimum of 1.5-inches of height clearance, unless the top is recessed as in this application.

Several aftermarket companies like Rick’s Tanks, Rock Valley, and even Detroit Speed offer tanks for specific vehicles such as early Camaros, Chevelles, and other cars. A stock tank could also be modified to accommodate a late-model module by using a VaporWorx weld-in mounting ring.

This cutaway of a Rick’s Tanks tank shows how the module sits in the tank. This optional system includes corner siphons and dams that reduce fuel slosh. This would be for a high-end, Pro Touring handling effort and would not necessarily be necessary for a typical street car.

There’s far more to returnless PWM systems than we can fully detail in this story, but VaporWorx offers more details and information on its website. Carl encourages potential customers to do their research with regard to other systems to compare the benefits of a VaporWorx system. That was exactly the effort we made that led us to this story.

The VaporWorx approach is not the least expensive so it probably isn’t for everyone. But for the discerning builder, long-distance hauler, and autocross/track day enthusiast, there are certain benefits you won’t find anywhere else.

About the author

Jeff Smith

Jeff Smith, a 35-year veteran of automotive journalism, comes to Power Automedia after serving as the senior technical editor at Car Craft magazine. An Iowa native, Smith served a variety of roles at Car Craft before moving to the senior editor role at Hot Rod and Chevy High Performance, and ultimately returning to Car Craft. An accomplished engine builder and technical expert, he will focus on the tech-heavy content that is the foundation of EngineLabs.
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