True SStreet: The Science Behind Street/Strip Fuel Systems

The fuel system: simple, yet in some regards, complex. In this text, we’re going to peel back some of said complexity, specifically in regards to engineering a fuel system for a high-horsepower, street and strip machine.

Our Project True SStreet is a street-and-strip 2010 Chevrolet Camaro that’s powered by a Chevrolet Performance LSX376-B15 crate motor topped with a 4.5-liter Whipple twin-screw supercharger, producing 1,025 horsepower at 6,600 rpm. That kind of power, plus the demands of stop-and-go driving places added importance on the fuel system. But as Weldon Fuel Systems’ Jim Craig notes, a fuel system isn’t a perfect science, and there’s no need to overthink it.

“We want to keep it simple,” Craig continues, as we delve into the topic of designing a fuel system for a street-strip vehicle. He explains that the first variable to cover is the type of fuel that’s going to be used in the car — is it going to be pure racing fuel, pump gas, or perhaps ethanol? This is key for a couple of different reasons: one, different fuels contain varying energy contents, meaning it requires more or less fuel to be flowed depending on the fuel choice. E85, for example, burns faster than gasoline, and the fuel system has to be able to keep up; second, the wrong fuel mated with the wrong fuel system components will corrode the internal seals and parts, leading to leakage and failures. 

“Is there a possibility of it being oxygenated, like a Q16? Or an oxygenated E85? These fuels can be a whole different animal, where you have to look at fuel pump sizing, fuel lines, and system components to keep the fuel from doing damage,” Craig notes. “If you run an oxygenated fuel, you can’t have any bare aluminum fittings in the system. Guys get away with the fuel rails, but as you’re moving the fuel through the system, the oxygenated fuel will corrode the parts. You’ll see a white powdery residue in the system.”

You always look at the total amount of fuel pressure, base plus boost, as where the total calculation comes from. When I size a fuel pump for a customer, I go to total fuel pressure. – Jim Craig, Weldon Racing

In regards to fuel choice relating to fuel system requirements, Craig noted the following math:

Producing 1,025 flywheel horsepower with the LSX376, our combination requires a minimum of 140 gph (gallons per hour) at 60 psi on gasoline to support said horsepower. Craig arrives at this number by figuring the maximum system pressure of 42 psi added to a hypothetical 20 psi of boost. If we were to switch to E85 or a straight ethanol fuel, we’d need to add 30 to 40 percent to that calculation to ensure the system — the pump, filters, lines — are sized correctly so we don’t shortchange anything.

While fuel flow calculators and varying formulas exist, Craig says he looks at a horsepower rating and then takes a more analytical approach to the elements in play. Using our example, a Whipple supercharger is regarded as an efficient supercharger, and at 10 psi of boost, Craig estimates it requires about 100 horsepower to turn the supercharger. As such, one would need to add about 10 gph to the calculation to account for the parasitic horsepower loss.

“Depending on the model and boost, you might be looking at upwards of 600 horsepower to drive the blower. If it were a turbo, there is no extra fuel needed, because a turbo is essentially free horsepower. If it’s nitrous, you look at the total amount of horsepower that you’re making. You always look at the total amount of fuel pressure, base plus boost, as where the total calculation comes from,” Craig says. “When I size a fuel pump for a customer, I go to total fuel pressure.”

“In regards to blowers, I suppose you could look at it as a percentage of your blower overdrive, but I still go to worse-case-scenario and at what total pressure?” Craig explains.

As you might surmise, a naturally-aspirated and turbocharged engine of roughly equal horsepower would have very similar fuel demands for this reason.

Weldon — and any fuel system manufacturer worth their salt — will generally factor a safety margin, if you will, into the fuel system for a given combination. This is done to account for system losses — the hoses, lines, and fittings — and the actual use of the vehicle. Drag racing applications are going to require more fuel for the potential of where the customer might go with the car, while someone with a pure street car may settle on a given combination and leave it alone.

“I throw about a 30 to 35 percent add-on to cover that,” Craig shares.

When it comes to fuel pumps, Craig says the key thing to look for is low amp draw at system pressure and also the flows at that given pressure. “Using our example, if the base is 40 psi and we’re putting 20 psi of boost to it, we’re at 60 psi. You have to look at what the flow is with that particular pump at 60 psi to make sure that you have enough pump to cover it. So the most critical thing in sizing a pump is flows and amp draws, at pressure. Because you can have a pump that’s advertised enough flow, but it’s at a lower pressure, and doesn’t show amps, so when you get to the required system pressure, there isn’t enough volume.”

In our build, we utilized Weldon’s D2035-A pump, which flows a minimum of 180 gph at 80 psi and draws in the neighborhood of 20 amps. At 60 psi, Craig puts the flow numbers in the vicinity of 200 gph. The less system pressure there is, the more flow you have — a fuel injected engine at 50 psi will support around 2,000 horsepower while at 80 psi that rating falls to 1,800 horsepower.

…let’s say you’re making 1,000 horsepower on the street, you need 140 gph … but that’s at 80 psi. Let’s back up the flow curve, and you’re at base pressure of 40 or 50 psi, now you’re moving 200-some gph through the system as soon as you turn the fuel pump on. You don’t need that on the street. – Jim Craig. Weldon Racing

Jumping over to the bypass regulator, a properly-sized return orifice (not an AN line size, but the internal diaphragm assembly that establishes the system pressure) is one of the keys that Craig notes when piecing together your fuel system. This orifice should adequately match the amount of fuel volume you’re trying to push through the system. “Ideally, with this engine you’d need to have at least a 1/4-inch return hole, or orifice, to accommodate 200 gph. As long as your return orifice is sized to the pump, .250-inch and higher, you’ll be able to accommodate 200 gph or higher through that orifice and still maintain your system pressure under wide-open throttle and no throttle. It essentially allows for fuel pressure response so you don’t have that drop-off in fuel pressure.”

Craig says ideally you don’t want to go under .200-inch return orifice with a regulator, as at that point that regulator may well become the restriction in the system. Commercially available, he says, it would be difficult to over-size a regulator.

Weldon markets one basic size of constant-flow regulator, with some variation in its makeup. Ours is the A2040-281-A-120, which is intended for fuel-injected engines and is adjustable between 28 and 110 psi. As Craig notes, most fuel injected engines are between 40 to 60 psi as a base. The regulator also sports a boost port to compensate for fuel pressure as your boost increases, and a .821-inch bypass return orifice, which Craig says is sized to maintain pressure operationally with any of Weldon’s electric fuel pumps.

Moving to lines and fittings, sizing is dictated by the volume of the pump. Upon determining what is the pump capable of flowing, Craig and his team then look at the size.

“If you’re trying to draw 200 gph through the system, you need at least a -10 line all the way through. If it’s above 200, you’ll want to go to a -12.”

Street Versus Strip

An electric fuel pump, as most know, runs at a constant speed, regardless of the fuel demands of the engine at a given time. It simply circulates back through the regulator to the tank and continues the cycle. In drag racing, where the engine may only run for a couple of minutes at a time, this doesn’t generally become cause for concern. But if you’re driving for miles — or perhaps hours — at a time, in stop-and-go traffic, well that’s a different scenario entirely.

You see, as unused fuel cycles back to the tank and continually moves through the system, it heats up, and if it’s a warm day outside, you can expect even greater heating of the fuel over time.

“What happens is, let’s say you’re making 1,000 horsepower on the street, you need 140 gph … but that’s at 80 psi. Let’s back up the flow curve, and you’re at base pressure of 40 or 50 psi, now you’re moving 200-some gph through the system as soon as you turn the fuel pump on. You don’t need that on the street,” Craig explains.

This is where a fuel pump controller comes into play, as it can be programmed to slow the pump volume down, thereby drawing less fuel from the tank when it’s not needed, and increasing it when it does.

“If you’re in traffic, you don’t need that pump operating at full speed. When it is, you’re pumping at that pump’s maximum volume. When it does, that fuel starts to get warm, and pretty soon the tank is beginning to get warm, the fuel can begin to boil, and you get into vapor-lock and other assorted issues,” Craig continues.

It takes a lot of fittings, swivels, and adapters to plumb a fuel system. Seen here is the wide assortment of pieces needed to plumb True SStreet, all from the folks at Russell Performance.

Craig recommends with any of their electric pumps (with the exception of their in-line pumps) the use of a fuel pump controller for street use, without question.

“There are other ways we’re skinning that proverbial cat now, where guys are making over 1,000 horsepower, and they’re keeping their stock tanks and pumps and then utilizing a secondary, auxiliary pump when they need it.”

To Overbuild or Not?

Back on the topic of matching a fuel system to your current and future needs, Craig said he always asks, “what is your plan? What are you going to do with this thing? Is it is a true street car, or are you going to convert it specifically into a racecar. What’s your power adder? Take a look at all of that and you can get an idea of where you need to be.”

This decision, as noted previously, is an important one, because if you were to oversize the system to allow for wide-open-throttle track use, but you’re only going to the track on rare occasion but mostly daily-driving the car, you’ll quickly drift into scenarios of overheated fuel and vapor-lock.

“A guy may never take his car to the track, but you can’t just size the fuel system for that. You have to take into account that he may take it to the track once, and you don’t want to burn the motor up because you don’t have a big enough pump,” Craig says. “But on the other side of the coin, you could go in with a large fuel pump to grow into, but if you go too big the heat problems will come sooner rather than later. Then the customer has more failure due to that, and it’ll be pump failures, because it’s cavitation and all kinds of gyrations within the fuel system. That’s where we have problems.”

Fuel choice, again, comes into play on this topic; many racers will tend to switch fuels from the street to the strip, and the fuel can greatly alter fuel system demands.

Can you get away with under- or over-speccing a fuel system for a given scenario?

“Sure you can,” Craig says. “I have import guys that do it all the time. They might drive on the street with E85 but when they get to the track they convert over to methanol. E85 uses twice the amount of fuel. So now they’re well within range, but they put up with it on the street. They understand the likelihood that if they drive it a little too long, they’re going to be encountering vapor lock and fuel boil and erratic pressure.”

Weldon generally aims to keep a fuel system spec’ed to the maximum horsepower of the engine, so that the customer isn’t over-fueled. Craig notes this is very much a case-by-case basis thing, depending on precisely what the customer intends to do with the car. In the event that engine or chassis dyno numbers aren’t available, he and his team can often take engine size and the power adder into account to estimate fuel system needs. 

“Many of the numbers we get are a bit inflated. They’re looking in magazines and coming up with numbers, but you have to be careful not to over-fuel a car. Some customers feel they can’t have too much fuel, but you definitely can. So we have to be realistic about that engine and what it’s producing.”

This comes down to not the pump, but the entire system — say for example you have a given pump but undersize the inlet line, will put a significant and damaging load on the pump. Or, if you used the proper -12 inlet line, but choked it down with only a -10 Micron filter, you’d run into similar problems.

“It’s not an exact science, and hopefully everyone has the same thought,” Craig states in closing. “There are just so many variables that come into play, with the fuels, the power adders, the customer, and you can’t sell them short and you can’t oversell them, because either way, it comes back and bites them. So you have to walk a real fine line, but enough to cover them if they’re going to roll to that next level. Because the guy that leaps and jumps, or runs E85 today and ethanol tomorrow, that whole combination changes completely — it’s like they turned the car over and dumped everything out and put something new in it, and everything changes at that point.”

Plumbing The Fuel System

Building an adequate fuel system for a street/strip machine doesn’t stop with the pumps, regulators, and filters — the hard parts, if you will. As Craig noted, sizing of your AN fittings and hoses is key to flowing enough fuel to suit the engine’s demands. But fuel compatibility and reliability are both key, as well.

For the fuel system on True SStreet, we turned to Russell Performance, a division of Edelbrock, for an array of hoses, fittings, and adapters to plumb the fuel system from the trunk up to the fuel rails and back.

We began with Russell’s Pro Classic II hose, a traditional-in-appearance hose made with an all-black nylon fiber braided outer cover over a Chlorinated Polyethylene (CPE) synthetic rubber inner line designed for abrasion resistance. Russell designed this hose with the intricacies of an engine compartment in mind, as the CPE inner liner sports a bonded, multi-braid stainless wire so you can bend it around tight radiuses without it collapsing.

The main thing that racers were after when they saw this hose line was weight. John Urist switched over and found they were 44-percent lighter than our old braided stainless hoses. – Smitty Smith, Russell Performance

The ProClassic II has a maximum working pressure of 350 psi and is compatible with gasoline, oil, and antifreeze. Those running methanol or E85 will, of course, want a PTFE-style hose (pump gas containing 10-15-percent ethanol is fine, according to Russell). The hoses can also withstand temperatures from -40 to 350-degrees Fahrenheit, meaning it’s right at home on mid-summer or mid-winter stop-and-go driving as much as it is on the dragstrip.

According to Russell’s Smitty Smith, it was discovered early on by R&D drivers like Billy Glidden and John Urist that any vacuum greater than 27-inches, the hose would collapse. And so they outfitted the hose with inner coils that act as wide-banded spring inside to prevent such scenarios.

The inside layer of the ProClassic II are made from extruded CPE synthetic rubber, while the outer shell is a high-quality nylon fiber braid for flexibility and abrasion-resistance.

The hoses come in -4, -6, -8, -10, -12, and -16 AN sizes, which mate directly to the crimp-on, full flow hose ends from Russell that we used in our build-up.

“The main thing that racers were after when they saw this hose line was weight. John Urist switched over and found they were 44-percent lighter than our old braided stainless hoses. Drag racers are ‘anal’ about weight, and John’s testimonial wasn’t half, but it was pretty close.”

Russell’s tapered hose ends — available in crimp-on and AN mechanical (we used the latter for our build) — are machined from aluminum and anodized black, which protects the material from erosion from methanol and E85. All of the ends are swivel in design, as well, so clocking them to navigate fuel lines around the engine bay are a cinch.

For our combination, we utilized -12 AN fittings and line from the tank to both the pump and the pre- and post-filters; from the post-filter to the Y-block up front is -10, at which point it’s necked down to -8 to the fuel rail inlet and -8 from the rails back to the regulator. From the regulator back to the tank is likewise -8.

Stay tuned, as now that we have the fuel system all wrapped, there are just a few additional projects to wrap up Project True SStreet, including the wiring, exhaust, the addition of a new driveshaft, and the installation of the seat and window net.

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About the author

Andrew Wolf

Andrew has been involved in motorsports from a very young age. Over the years, he has photographed several major auto racing events, sports, news journalism, portraiture, and everything in between. After working with the Power Automedia staff for some time on a freelance basis, Andrew joined the team in 2010.
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