The line between street car and race car has been continuously blurred thanks to drag-and-drive competitors. Dual fuel systems have become popular in the drag-and-drive world because it gives racers the ability to run different fuel on the street and in race mode. In this article, we’re going to take a look at what goes into building dual fuel systems for a high horsepower drag-and-drive application.

Dual fuel systems aren’t a new thing, however, drag-and-drive racers have used modern technology to elevate what you can do with these fuel systems. Many racers will use a dual fuel system to feed the engine basic 93-octane pump gas while on the street, and then be able to run methanol or another type of race fuel when it’s time to crank up the power.

Why Run A Dual Fuel System

Typically, vehicles in drag-and-drive events that are using dual fuel systems are making in the 1,500-to-3,000-horsepower range. These combinations are going to need a huge fuel supply when at the track to support that amount of horsepower, but when they’re on the street they don’t use nearly that much fuel. The type of fuel they use in race mode will also dictate the need for dual fuel systems. It’s not really economical or practical to log over 1,000 street miles during a drag-and-drive event while running on race gas or methanol.

“Unlike your typical track-only car, a drag-and-drive car is going to be running and driving a lot longer. That additional run time could be very hard on a mechanical fuel pump, especially when you add in the time spent idling in traffic. When you pair the mechanical fuel pump system with a fuel system with an electric fuel pump, you create a system that can support more horsepower and be very reliable,” explains Aeromotive’s Jackson Lueg.

Big 3 Racing’s Chuck Stefanski and his 1981 Pontiac Grand Lemans wagon have won drag-and-drive events. The Pontiac is powered by a big-block Chevy with a massive F-3 ProCharger hanging off the front of it. This potent combo runs in the low-seven-second range with the engine running on methanol in race trim. Stefanski’s car is the perfect application for dual fuel systems

Running a dual fuel system allows a drag-and-drive racer to optimize their race-mode fuel system. You don’t have to worry about driveability on the street, you’re just trying to provide the engine all the fuel it needs to make as much horsepower as possible.

We mentioned fuel mileage and availability being one reason why a dual fuel system is perfect for high-horsepower drag-and-drive builds. According to Stefanski, another reason is that running on pump gas when possible saves wear and tear on the engine.

“Running on pump gas at idle, while on the street driving, or moving through the pits saves wear on the engine since the methanol will wash your rings out. I’m also not contaminating my oil nearly as much with the methanol since we’re not running on it all the time. The system cuts down on maintenance and allows us to concentrate on other things during a drag-and-drive event,” Stefanski says.

Stefanski wanted to set his system up to make the change between pump gas and methanol automatically. So, when his Holley Dominator ECU sees a certain level of boost, it will stop feeding the engine pump gas and start the flow of methanol from the race fuel tank that Stefanski set up. This helps limit the amount of methanol the engine sees when it’s running. It also eliminates the need to physically change the fuel system over from street to race trim during a drag-and-drive event.

Street And Strip Solutions

Typically, the pump-gas side of the system is going to be the easiest to set up. You just need to know how much fuel the engine will need to run on pump gas. To find out how much fuel is needed you’ll use the formula to find the fuel consumption in lbs/hr of an engine, Horsepower x Brake Specific Fuel Consumption BSFC). So, if your horsepower goal is 800HP and the BSFC for the fuel is .55, the calculation would be 800 x 0.55. That would tell you that 440 lbs/hr injectors are required. You can learn more about what goes into this calculation here.

Once you have your fuel demand figured out, you can choose the right injectors and fuel pump to meet that demand. Injectors come in all sizes and shapes, so to find the right ones, you’ll need to look at their lbs/hr rating. This will tell you how much fuel they can flow. Fuel pumps will have a Gallons Per Hour (GPH) rating and will also list how much horsepower they can support. You’ll need to pay attention to the type of fuel the pump can support to ensure it will work with your application.  

You’ll also need to make sure the fuel lines you run will support the flow that’s required to keep the engine fed. If you’re at 350 horsepower or less -5AN will be fine. When you’re in the 350-450 horsepower range -6AN is going to be required. Once you step into the 450-650 horsepower range -8AN fuel line has to be used. After you climb into the 650-1,000 horsepower zone -10AN fuel line has to be used. If you’re going beyond 1,000 horsepower it’s time to look at -12AN and above fuel line depending on how much power is in play.  

For Stefanski’s fuel system, an Aeromotive 340 fuel pump was used on the pump-gas side. This pump made the most sense for the fuel system since it can support up to 1,000 horsepower and is very reliable. The 340 also provides versatility with how it can be mounted, this is important when you’re building a custom fuel system.

The Race Side Of Things

Now, the race-gas or methanol fuel system is going to be more complex. There aren’t any templates out there for these, each system is based on the fuel flow needed to support the engine. After talking with the team at Aeromotive, it was decided that a Lil’ Bertha pump from Waterman Racing Components would be the best fit for Stefanski’s application. These mechanical fuel pumps are highly customizable and can be built to fit any fueling need. An added bonus is the mounting options that Aeromotive offers that work with the ProCharger drive system Stefanski uses on his engine.

“We worked with Waterman to make sure we got the correct pump for the methanol side of the fuel system. They have a chart that takes into account what RPM you’ll be spinning the engine to and how much horsepower you plan on making to ensure you get the right flow out of the pump. Each pump uses different gear sizes for fuel flow. Since we need around 18gallons-per-minute they set our pump up with the 0.800-inch gear,” Stefanski says.

Plumbing The System 

The plumbing, regulator, and fuel filter side of the system is just as important as the pumps themselves. For fuel lines, you’ll want to look at a minimum of -12 lines to feed over 1,500 horsepower. To get the optimal fuel line size for your specific application you’ll want to see what the fuel pump company recommends based on what their product can support.

“Not all regulators are the same, there’s more to it than port sizes. It’s important to match the regulator to the pump and understand the volume potentially being bypassed at the regulator and returned to the tank. The appropriate spring inside the regulator is critical to getting the pressure where you need it,” Lueg states.

Lueg also goes on to explain more about the size of the filter and how much flows. “The volume of fuel moving in a mechanical system requires a massive amount of filter surface area. You need to make sure the filter is big enough so it doesn’t impact flow, while still protecting the injectors.”

All of that plumbing has to connect to something to feed the engine fuel. A well-designed system is going to have one larger tank that will be used for pump gas driving. You want to the biggest tank that will fit inside the space that’s available so you don’t have to stop as often when driving in between tracks. The race gas tank won’t need to be as large since it won’t be used as much. A five-gallon or less sized tank would be fine.

The right intake is a key component of a dual fuel system. Having dedicated sets of fuel rails that are properly placed on the intake runner is critical. This is going to let both fuel systems do their job and allows you to correctly plumb each side of the fuel system.

The final piece of the puzzle is the intake manifold. There are different styles of intakes available based on your power adder of choice, but Stefanski recommends using a true dual fuel rail setup.

“We learned that you really need to have two sets of fuel rails and two sets of injectors to help the system function at its best. I’ve seen setups that have 16 injectors on a single rail and two injectors per cylinder, but that doesn’t work best for these high-horsepower applications. I had Thomsen Motorsports make an intake for my engine that supported two separate rails and sets of injectors. That allowed us to plumb each rail with the correct-sized fuel lines, which is really important on the methanol side of the fuel system,” Stefanski states.

Injector selection really comes down to how much horsepower you plan on making and the type of fuel you’re going to run. Earlier we covered how you calculate fuel demand for the fuel system and that’s also going to tell you what size fuel injectors you need. The big difference between a normal fuel system and a dual fuel system is you’ll need to run the calculations for both the pump gas and race gas side of the fuel system. 

A high-horsepower drag-and-drive car will benefit greatly from dual fuel systems. When the system is properly designed and built it opens up just how hard you can push a vehicle without sacrificing its ability to be driven on the street.