Plumbing 101: Part 4

The fuel system in your car has to start and end somewhere. The best place to start laying out the system is the gas tank (whether it's a fuel cell or conventional gas tank).
Plumbing 101: Part 4
The fuel system in your car has to start and end somewhere. The best place to start laying out the system is the gas tank (whether it’s a fuel cell or conventional gas tank).

We’ve been taking a detailed look at plumbing your racecar or hot rod on these pages. We began the series by figuring out how AN works, and then we went on to examine fittings along with a couple of great examples of high quality hose. All of these components are geared directly at high performance applications, and all will work with common automotive chemicals. This time around, we look at the various ingredients of the fuel system. Essentially, in order to build something like a proper fuel system, you have to know where the plumbing starts and where it ends. Along the way, you’ll find that you also have to plug in pieces such as filters, regulators and perhaps return lines.


Fuel System Key Ingredients:

The fuel system in your racecar or hot rod has to start somewhere and end somewhere. No surprise, I’m sure. While we won’t dig into the details of the actual hardware here (we’ve covered it previously), we’ll give you some insight into sizing and component placement.

Key ingredients in your fuel system include the gas tank (or fuel cell), the fuel pickup, a mechanical or electric fuel pump, a fuel filter, fuel line and/or hose and sometimes a fuel pressure regulator. The performance of the engine and the entire car will dictate whether or not you need to upgrade to something like an electric pump with a fuel pressure regulator. And of course if your racecar or hot rod has an EFI setup, you’ll definitely need an electric system of some sort. We’ll get to the fuel requirements later, but where do you really begin? The best place to start is at the source – gas tank or fuel cell:


Gas Tanks & Fuel Cells…

What should you use – a tank or a cell? Really, it depends upon the car. With a true street driven car, three or even five gallons of gas won’t go too far. Race cars use large amounts of fuel in short periods of time. Street cars and dual duty street-strip cars demand this on occasion too, but they also have to deliver the fuel over the long haul. There are quite a few similarities, but plenty of differences.

There’s more too: Many fuel cells contain an internal foam bladder. The purpose is to prevent fuel from sloshing within the cell, and simultaneously minimize the possibility of a fuel explosion due to impact in a crash. Some of those foam bladders can be “eaten” by what we call “pump gas” today. If you’re using a fuel cell on the street, you should contact the manufacturer to determine if it is safe to use the cell with pump gas (if the gasoline is laced with alcohol, be doubly careful).

Fair enough, but what if you want or need to keep the stock tank? We’ve dug into this before, but when using a stock tank, consider using a high flow pickup/sending unit (RobbMC is a good example). Holley also offers a great invention called HydraMat®. Holley’s patent pending design solves the problems associated with traditional fuel pick-ups in stock fuel tanks as well as racing fuel cells. During hard cornering, acceleration, stopping, inclines and low fuel conditions, fuel runs away from the fuel pick-up, which introduces air into the system, resulting in poor engine performance and even stalling. Seriously, HydraMat is the fix.

Plumbing 101: Part 4
(Photo credit to Holley) Holley has come up with a clever innovation called a HydraMat®. It’s designed as a unique fuel tank pick-up. See the text for more info.

According to Holley: “Surface tension and fluid wicking are the secrets of the HydraMat, giving it the amazing ability to draw from nearly any area that has contact with fuel and then store it in its internal reservoir. As an area of the HydraMat is uncovered, the tiny pores of the media seal off through surface tension, forcing fuel to be contained in the reservoir and drawn from other areas of the mat where fuel continues to be available. The sheer size and coverage area of the HydraMat allows it to pull fuel from virtually any area in the tank or cell, eliminating the need for specialty reservoirs and pick up pumps saving cost and greatly reducing complexity.”

HydraMats are available in various sizes and shapes to fit a variety of stock fuel tanks and/or race fuel cells. Basically, you fit it in the base of your gas tank and plumb the pick-up to it. They can be affixed to the base of your tank with a click bond method or magnets. Holley offers both, along with special bulkhead plumbing kits. Here’s a link to a good video that shows how it works:


Fuel Pumps…

How much fuel do you need? According to Holley Engineering: “Typically, at wide open throttle, full power, an engine requires 0.5 lbs. of fuel per horsepower every hour. A gallon of gasoline weighs approximately 6 lbs. Therefore an engine rated at 350 horsepower will require about 175 pounds (29 gallons) of fuel every hour.”

(350HP x .5 lbs = 175 lbs of fuel 175 lbs/6 lbs = 29 gallons per hour)

Plumbing 101: Part 4
Consider the fuel pump you’ll need for your application – mechanical or electric. There are all sorts of different combinations out there, but before you plumb your car, you’ll need to “nail down” the pump location.

Holley states: “The relationship of pressure to volume is inversely proportional. That is, as pressure increases the volume will decrease, everything else being equal. A certain amount of fuel pressure is always required to maintain engine performance by assuring that fuel is available on demand. Also, other factors and conditions must be taken into account such as acceleration G-forces and friction within the fuel system itself. At the same time an adequate fuel volume is needed to ensure that the proper amount of fuel can always flow to the engine, especially during peak demand situations. A basic understanding of this critical pressure/volume relationship is needed when designing the proper fuel supply system for your vehicle.“

The bottom line here is, the fuel pump (whether it is a mechanical or an electric example), must be capable of supplying the demand of your engine at wide-open throttle. Several great examples are shown in the accompanying photos.

The type of pump obviously dictates the mounting location; keep that in mind when you’re laying out your fuel system plan. Mechanical pumps are installed on the engine and are designed to draw fuel, while electric pumps are typically installed at the rear of the car, where they push fuel.



Plumbing 101: Part 4
Another critical component is the fuel filter. Don’t bother with any of the small filters or the plastic jobs. You need something that will not present a restriction in the line. These big inline Holley jobs are perfect for the task.

Fuel is dirty. No surprise, we’re sure. You need to filter it, and it’s a good idea to use a high capacity in-line filter, or even a pair of them – one before the pump (pre-filter) and one after. Of course, there are a lot of different fuel filters available today. No secret. You can even track down jobs that are pure vintage in the looks department. Unfortunately, from a flow perspective, some of those vintage fuel filters don’t do so well. A good option is Holley’s latest line of billet in line filters. They’re huge capacity jobs machined for -8 AN and larger fittings. Holley’s filter easily disassembles, allowing you to access the internal wire mesh filter. Typically, these filters have a GPH flow rating of 260 or so gallons per hour. Obviously for the vast majority of situations, these filters will not act as a restriction in the system.



Before the fuel enters the fuel line or fuel rail(s) in your car, and ultimately before it reaches the fuel bowls or the fuel injectors, some sort of device is (often) necessary to harness the flow and pressure of the fuel. That job belongs to a fuel pressure regulator. For EFI applications, a regulator is mandatory. For carbureted applications with fuel pump pressures higher than approximately 7.5 PSI, a regulator is required too. For these carbureted applications, too much fuel pressure for a given needle and seat assembly can overload the needle and seat and may cause flooding or drivability problems. In the case of Holley examples (shown in the accompanying photos), each fuel pressure regulator is fully adjustable, so regulating the fuel pressure to fit your engine requirements is a simple task.

Plumbing 101: Part 4
For many fuel delivery systems, you’ll need a fuel pressure regulator. Typically, these are mounted on either the inner fender or right on the engine. This example is designed for a return line system.

When it comes to regulator mounting, choices are limited. Some racers mount them on the engine; some mount them on the inner fender well (citing engine vibration as the reason). Take your pick. We’ve done it both ways without ill effects.

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