Under Pressure: How S&S Feeds An Extreme Diesel Race Engine

Your father’s diesel engines were known for being dirty and loud, and while unrivaled in longevity and efficiency — at least relative to their spark plug-equipped counterparts at the extreme end of the spectrum — they weren’t exactly all-out performers in the racing world. But diesel performance has come a long way, thanks in part to the efforts of companies like S&S Diesel Motorsport, who have driven technological leaps in fuel systems and engine management systems. The result are efficient, clean-burning, and quiet race engines capable of producing the kind of horsepower to run with their gas and methanol-fueled competitors.

“There have been diesel engines for decades, but previous generations all had mechanical fuel systems — in the early 2000s the OE’s were met with further emissions requirements and reduced noise, and that drove the technology to these electronic fuel injection systems,” explained S&S co-owner Luke Langellier.

Langellier formerly specialized in engine development and performance calibration at Cummins, while business partner Andrew Stauffer was an engineer working on fuel systems at Bosch; the two combined their skills into a potent combination at S&S. Today, the company specializes in common rail, electronically-controlled, high-pressure fuel systems for modern diesel engines — fuel pumps, injectors, and relief valves for everything from 50-state-legal street vehicles to 3,000-plus-horsepower, competition-specific applications. It also delves into the electronics side, including engine control units, power distribution modules, relays, and complete wiring installations.

The cars of S&S customers and development partners Jeremy Wagler (left) and Ben Shadday.

Thanks to its innovative, industry-renowned products and services, S&S was chosen to play pivotal roles in what may soon become the first 3-second, diesel-powered machines in the world.

These cars, innovative in their own right, have S&S’s fingerprints all over them, from the fuel pumps and injectors to the wiring harnesses and the MoTec electronics that provide the instructions to it all. These include the Pro Modified-style 1963 Corvette of Done Right Diesel’s Ben Shadday, which was a project that included considerable support from Tony Derhammer at Hammertech Race Cars, and a screw-supercharged dragster owned by Wagler Competition Products’ Jeremy Wagler.

Shadday’s and Wagler’s machines are both fresh projects, only making their first runs this spring. The Corvette features power from an all-billet Cummins 6.7-liter-based mill built upon a Wagler block and cylinder head, with a Garrett GTX55 turbocharger. Wagler’s dragster, meanwhile, sports power from a GM Duramax LBZ-based engine, with a Wagler billet cylinder head and a prototype PSI supercharger built specifically for the needs of diesel applications. Both are rather extreme, showcasing the outer limits of diesel engine performance — and those outer limits include the fuel system and electronics, which are as cutting-edge and refined as they come. As such, what better way to provide a glimpse into the world of high-end diesel performance than with these machines.

Under Pressure: Common Rail Diesel Fuel Systems

Diesel engines, devoid of any external source of spark for combustion, operate by compressing air in the cylinder to such a degree that air temperature rises rapidly, thereby spontaneously igniting the fuel introduced into the engine. It is, in simple terms, self-ignition. In order for this process to work efficiently, the fuel has to be injected at a high pressure so as to atomize in the combustion chamber. And unlike a conventional gasoline or methanol fuel system that may require 150-200 psi at peak (with port fuel injection), fuel is forced into a diesel engine’s cylinders at more than 30,000 psi on the top end, and that creates unique demands of fuel system components not found with a Hemi or an LS. Even the latest direction-injection LT and Coyote engines are only operating at around 2,000-3,000 psi.

Wagler's screw-blown Duramax (left) and Shadday's turbocharged Cummins.

Modern diesel engines use what is known as common rail, which involves the use of a high-pressure fuel pump that feeds into a rail, which is essentially an accumulator, and delivers the fuel to the individual injectors. High-pressure common rail, or HPCR, is essentially identified as a high pressure pump and a common accumulator. This is a departure from older, mechanical systems that would have as many plungers in the pump as there were cylinders, and a fuel line from the pump to each individual injector. Each time a plunger would generate pressure, it would fire that cylinder. Common rail, though, relies on one high-pressure pump that feeds to the rail — the fuel is then deposited through a ‘jumper line’ to the individual injectors and into the cylinder. The fuel pressure is always there at the injector, and the conditions that are calibrated into the ECU instruct the injector to fire at the appropriate time.

A common rail fuel system is a really obedient creature — it just does what it’s told. – Luke Langellier, S&S

“The beauty of this is that it’s fully flexible — you can have different startup injection timing versus RPM versus fuel quantity versus about anything you want,” Langellier explains. “It can also be used with different injection pressures as another ‘lever’. This is used widely in racing and OE; in different situations you want different rail pressures, which alters emissions characteristics and power and noise, depending on the pressure and timing and everything that you’re at.

“The common rail system can also fire multiple injection events in the same cycle, and that’s how the vehicles have gotten so much quieter,” Langellier continues. “Engine noise since the early 2000s has gone down drastically, and that’s related to not just one injection event — one loud bang as the piston approaches top-dead-center — but actually it’s being able to inject what’s known as a ‘pilot injection’, which is a small fuel quantity while the piston is coming up to get the fire lit. You get less of an abrupt combustion noise that way.”

Langelier adds, “a common rail fuel system is a really obedient creature — it just does what it’s told.”

The heart of the common rail system on these cars is Bosch’s heavy-duty and high-performing CP3 fuel pump. These were found in all 2001-10 Duramax and 2003-2018 Cummins vehicles. But these aren’t any ordinary CP3, as S&S fully strips them for modifications from top to bottom to increase output at high RPM, well beyond their stock capability. It also adds “direct-feed” blocks that it manufactures, optimized for drag racing.

“The CP3 base pump design is used all over the world on a lot of different engine platforms — it’s a really robust pump design. It’s pretty heavy, forged body…it’s a stout pump, but it has to be to withstand such high pressure,” Langellier says.

A lot of common rail applications using the CP3 operate at 1:1 with engine speed and essentially use the camshaft as an idler. “There’s a lot going on, and obviously the pump RPM is changing dramatically as it’s going down the track, shifting gears and everything, but the pressure is — assuming it’s a well-controlled system — whatever we command it to be,” Langellier says.

A 14mm CP3 high-pressure pump with SP-3000 supply pump (low-pressure) on the front.

The fuel system on these extreme machines utilizes not one, but two CP3 pumps, spunin reverse rotation through a gearing system driven by the camshaft inside a Wagler-designed front cover. On the Corvette, a smaller “lift” pump, or supply pump, is operated via the dry sump oil pump gear, drawing fuel from the tank at low pressure to both CP3’s. Wagler’s dragster features a small Waterman supply pump. In factory form, CP3’s have a gear-driven suction pump on the front for drawing fuel, but S&S performs a “delete” on that operation. Fuel pressure from the tank to the CP3 is low enough (perhaps as low as 15 psi, but upwards of 200 psi on these race machines) that flexible braided line can be used, but from there on, hard-line is required to cope with the eye-popping pressures. At about 2 millimeters in wall thickness, Langellier says these hard alloy lines (made by a third party) are rather impressive pieces in their own right.

The CP3 pumps are inlet controlled, meaning at the inlet of the pumps are fuel control actuators, which are electronically-controlled metering devices (similar in theme but not in function to a fuel pressure regulator). These actuators are a current-to-flow device, or volumetric flow-based. The two CP3’s are arranged in a “common manifold” configuration — a basic term Langellier uses likening it to a twin-turbo engine where each turbo feeds to a common intake manifold — but each feed to the common fuel rail.

(Left) the Waterman supply pump and two CP3 pumps on Wagler's dragster, and the high-pressure lines from the two CP3's on the front of Shadday's Cummins (right).

From there, the fuel is fed to the rail or rails (Wagler’s Duramax V8 engine has a rail for each bank) and on to the injectors. Because Wagler’s car has a rail on each side,  the two rails are tied to their own CP3, but a hard line behind the supercharger ties them together so that the pressure is equalized across the entire system.

While the goal — again, in a well-controlled engine — is to supply only the amount of fuel the engine needs, some diesel applications will have a spring-actuated relief valve on the rail to allow excess fuel to subside. 

A fuel rail from Wagler’s Duramax V8 engine.

Shadday’s car actually features two electronically-actuated (by the MoTec ECU) relief valves that send low-pressure fuel back to the tank in the event of a pressure over-shoot.

The CP3, in addition to its high-pressure side, features a gear-driven low-pressure feed pump on the front. In a factory Duramax configuration, for example, there is no electric supply pump, so the gear pump on the front has suction on it to draw fuel from the tank. That small pump further compresses the fuel to the case pressure, which feeds fuel into the pumping elements to help produce the extreme pressures. Factory Cummins applications have an in-tank pump.

Fuel pressure at idle is generally low, as the engines run better at low pressure, but in action, pressure rises exponentially under load — the Ordnance 2500 bar fuel injectors in Shadday’s car delivering as much as 36,259.43 psi.

Wagler’s dragster is a slight departure from diesel norms, as its large PSI supercharger cannot run “dry” and requires constant lubrication — as such, it features four Billet Atomizer injectors positioned at the top of the supercharger, between it and the hat, spraying a water/methanol mix. Controlled by the ECM, the mixture is being pulsed depending on the load on the engine


While its capabilities are multi-faceted, S&S is perhaps best known for its fuel injectors. In a diesel application, injectors face incredible demands, and as such, are impressive feats of engineering. And in an extreme diesel race engine, the injectors are to the CP3 as Batman is to the Robin, the Bonnie is to the Clyde — both are just as important as the other, and neither can do its job optimally without the other.

In addition to the very creation of these injectors, S&S takes great pride in its testing and calibration procedures, delivering as perfectly-matched a set of injectors as you can buy.

The Ordnance LE-T installed in a Wagler DX460 billet Duramax.

For most of its applications, S&S starts with a brand new, Bosch-based injector, and fully strips it…Langellier noting that in OE form they won’t deliver nearly enough fuel for the needs of race engines. When S&S is done with them, they are highly-modified, fully custom injectors. S&S uses an injector that is purpose-made in form and fit for the engine platform — this is because in a direct-injector setup, the injector mounts in the cylinder head itself and they are designed in tandem…it’s not an “upstream” injector arrangement like most gas engines where the injector is in the intake manifold.

A Duramax LBZ injector.

Wagler’s dragster uses a Duramax LBZ-based injector, while S&S turned to its aforementioned Ordnance 2500 bar injectors for Shadday’s Cummins. Langellier explains the latter is a higher pressure-capable injector with lower leakage going back to the tank, meaning you can make more power with the same pump output. The Ordnance units are a high-end injector, based on an original Bosch unit.

Because diesel injectors are under such high pressure at all times, and because they have to operate so quickly, the injectors are designed differently than a gas or methanol part.

Langellier explains, “The needle itself that opens and closes and allows fuel to be injected is not directly coupled with the solenoid. It would take too large of a solenoid, and be too slow to react to directly control the needle with solenoid electromagnetic force. Instead, it’s a pressure balance. The needle is held closed with hydraulic pressure created by the fuel pressure. There’s a small valve above the control rod and needle, and when the ECU commands to fire that injector, the solenoid opens a tiny valve which relieves the pressure on the top side of the needle. Pressure in the nozzle then is able to lift the needle and inject fuel through the nozzle directly into the combustion chamber. There’s pressure on the top and the bottom of it, and the whole thing is controlled based on how much pressure we allow on the top or bottom of that needle. That’s what causes it to move up and down and inject fuel at precisely the right time, and for the proper duration of time.”

The Ordnance injectors mounted in the Cummins cylinder head on Shadday’s Corvette.

Langellier adds that they are “pretty cool units, because they have to inject so fast. It has to be dead-on and really consistent so that they start fast the right time in relation to where the piston is, and it’s got to be the right duration of time. I’m a little biased, obviously, but they’re really a work of art, to operate at those speeds. This is an engine running at 5,000 rpm, and the injector is able to inject multiple events within the same cycle.”

“With any of these injectors, the tolerances and the precision required at these kinds of pressure levels and requirements is crazy. It’s to micron-type level in clearances and dimensions,” Langellier says. “Really, really subtle changes or adjustments to different parts of the injector will affect the output of the injector in different ways. There are different areas within that you would adjust or change, be it a slightly different shim or spring force, or changes to flow. We have specialized equipment that only looks at the quantity of the fuel injected, but it also looks at the rate at which it was injected. This is what really differentiates us — we look at not only whether you really got the same amount of fuel per cylinder, but since it’s direct-inject, it really matters the amount of time that fuel was injected in.”

S&S’s most advanced test bench can measure up to 10 injection events per simulated combustion cycle and can also measure the complete injection profile, or “rate shape.” It is also outfitted with a custom large volume rail that S&S calls “the bomb.” It provides enough volume to offset the fluctuation in rail pressure when the injector is fired. This allows for more accurate and steady pressure to be measured.

S&S refers to this measurement of rate and time as “rate shape.” 

As it’s starting to inject fuel, S&S can see, exactly as the injector is opening, the type of speed it’s starting to inject fuel at, as well as the peak flow rate, and the speed at which the injector is closing. Through its experience, its equipment, and detail-oriented technicians, it has mastered this principle, and the precision of the final product shows.

Nitrous oxide

Wagler’s and Shadday’s cars, along with other extreme diesel competition vehicles, utilize nitrous oxide systems that are typically plumbed into the intake manifold, and while this is usually viewed as (and ultimately is) for power enhancement, there’s a qualified explanation for it.

The nitrous lines (black lines) plumbed into the intake manifold.

“A diesel engine wants to run really lean compared to gas, typically,” Langellier explains. “The air/fuel ratio that a diesel engine runs at is much more ‘air’ than gas engines, so you really can’t go too lean. On gas cars, lean is mean until you melt something down, but on a diesel you really can’t do that in normal conditions. Most gas stuff runs at 14:1 or 15:1, and a diesel could be 30:1.”

Because a diesel engine effectively wants all the air it can get, the nitrous oxide acts as an oxygen carrier, providing more oxygen to burn during spool up to help with turbo spool at the starting line, and additional oxygen everywhere else on the racetrack.Beyond that, it is also a cooling agent — when the pressure change happens and nitrous changes form, it is super-cold, enough to freeze up lines. In a lot of cases, racers aren’t using intercoolers or cooling the intake charge in any fashion because of the extra weight and complexity, so the nitrous cools the incoming air.

Here you can see the plumbing for the NX nitrous oxide system that is plumbed into the supercharger intake manifold, along with the nozzles in the top of the supercharger for the introduction of the water/meth mix on Wagler’s dragster. Langellier says the further upstream the nitrous can be introduced on a diesel engine, the more time it has to cool the intake charge.

In a supercharged application like Wagler’s, a water/methanol mix with a separate MoTec-controlled set of fuel injectors and mechanical pump is plumbed into the top of the supercharger to cool the rotors. This was a unique project for the team at S&S and Wagler to undertake, and of course, its role presents some added challenges for a tuner, with two forms of fuel entering the combustion chamber.

“We’re introducing two different fuel sources, rather than just one — two fuel systems that combust at different conditions. One of them being direct-inject, and one indirect-inject. The direct-inject side of things, you don’t have to worry about it detonating unless you just advance the timing too far, but on the methanol, we have to be conscious of boost, compression ratio, timing, and rail pressure. Because if we run any of that too far off what it wants, we can create a pre-ignition, detonation type of scenario where the methanol is lighting off before we want it to, and creating excessive cylinder pressure and damage. So it really becomes a balancing act of methanol-to-water ratio, methanol quantity, boost pressure and compression ratio, and ignition timing.”

What S&S has learned on the racing side of the coin in developing fuel systems for extreme applications like these, has helped drive research and development on the parts it makes for your vehicle, and vice versa. S&S remains a brand that emphasizes street performance in diesel-fueled daily drivers and tow rigs, and its efforts have helped contrast today’s diesel engines from those of the past — as clean, quiet, efficient, and supremely-powerful machines.

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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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