ProMotor Engines: Engineering Reliable Horsepower from Road Racing to Top Fuel
Dennis Borem shares lessons from decades of NASCAR engine development, Trans Am competition and 12,000-horsepower nitro racing on EPARTRADE’s Race Industry Now
Building a race engine capable of producing impressive peak horsepower is one challenge. Building one that delivers the right power curve, survives its intended duty cycle and gives the racer a competitive package is another.
That distinction was at the center of a recent EPARTRADE Race Industry Now webinar, “Building Winning Road Racing & Drag Racing Engines: Engineering, Innovation & Performance,” featuring Dennis Borem, President & CEO of ProMotor Engines, LLC, and hosted by Joe Castello of WFO Radio.
Drawing on decades of experience spanning NASCAR Cup engine development, Trans Am road racing, vintage competition, USAC midgets and NHRA Top Fuel, Borem offered a detailed look at an engine-building philosophy in which horsepower, durability, precision machining and application-specific engineering are inseparable.
Horsepower With a Purpose
For Borem, an engine program begins by understanding exactly what the customer is trying to accomplish.
Road racing provides a particularly clear example. Unlike an engine built simply to maximize peak output, a road racing engine has to deliver usable torque and horsepower across a broad RPM range while surviving repeated acceleration, deceleration and extended periods under load.
Durability, Borem emphasized, is critical.
ProMotor Engines works with Trans Am programs ranging from sealed, cost-controlled TA2 engines to the considerably more powerful engines used in the upper levels of Trans Am competition. The difference illustrates one of the fundamental realities of race engine development: additional performance generally comes at the expense of operating margin.
Borem described every racing engine as having a figurative “fuse.”
A sealed engine designed to run multiple events can have a relatively long fuse. Move toward an engine producing 850 to nearly 900 horsepower, increase compression, optimize combustion and push RPM higher, and that fuse becomes progressively shorter.
The objective is not simply to make as much power as possible. It is to determine how much performance the application can justify while establishing an appropriate maintenance and service interval.
For one NASCAR-derived engine package, Borem described approximately 850 horsepower at up to 8,800 rpm as a durable configuration. More power is available, but achieving it can involve increased compression, improvements around the piston fireland and quench area, and reducing dead space in the combustion chamber.
The tradeoff is straightforward: more power can mean more frequent inspection and service.
Less Than One Percent: Engineering Consistency Into Spec Engines
In a sealed engine category such as TA2, the engineering challenge changes.
With strict limitations on what builders can modify, ProMotor Engines isn't attempting to find another 10 or 15 horsepower for one competitor. Instead, Borem said the goal is to keep engines extremely close in output.
ProMotor's TA2 engines are maintained within less than one percent of each other in power.
Once that consistency is established, maximizing performance becomes a combination of engine preparation, installation and trackside support.
Something as seemingly minor as a wiring harness positioned too close to a header can become a heat-related reliability issue. Identifying those details and helping racers extract everything available from a controlled engine package becomes an important part of the engine builder's job.
In less restricted Trans Am applications, however, ProMotor has considerably more freedom.
Intake manifold configuration can be used to tailor the engine's characteristics to a particular circuit and driver. At a fast track such as Road America, for example, Borem said a driver capable of exploiting the additional top-end power may benefit from a manifold worth another 10 to 15 horsepower higher in the RPM range.
At slower circuits, the priority can shift toward torque and corner-exit performance.
That makes driver feedback another engineering input.
“The more experienced drivers probably give you better input,” Borem explained, allowing the engine builder to match the power curve more precisely to how the driver uses the car.
Lessons From NASCAR's Horsepower Wars
Some of the webinar's most technical discussion came as Borem looked back at NASCAR engine development during an era when teams were aggressively searching for incremental horsepower.
Restrictor-plate racing created a particularly difficult engineering problem.
Borem recalled that an unrestricted engine producing approximately 750 horsepower could struggle to make 400 horsepower once severely restricted. That forced engine builders to rethink airflow and search for performance in areas that had previously received less attention.
One solution involved machined tubes installed beneath the restrictor plate in the intake manifold. ProMotor experimented with different radii and angles to manipulate airflow through the restricted opening.
Borem's explanation was simple: the device appeared to straighten the airflow, and more importantly, it made horsepower.
Compression ratios also climbed dramatically.
Before NASCAR established its current compression restriction, Borem said Cup engines were developed to approximately 19:1 compression.
Ring packages became another development area. Drawing on concepts familiar to drag racers, builders experimented with vertically gas-ported pistons and, in some applications, eliminated the second compression ring to create a two-ring piston package.
The objective was to reduce friction while improving ring seal.
Then came another important discovery: crankcase evacuation could produce measurable horsepower.
Finding 10 Horsepower in the Oil Pan
During dyno development, Borem's team experimented with aggressively evacuating the dry-sump oil pan.
They installed five bungs in the pan and connected a five-stage pump. During a dyno pull, the additional evacuation system was switched on.
The result was immediate.
The engine gained approximately 10 horsepower.
The concept was subsequently incorporated into the race car using an additional pump mounted near the rear differential with lines running forward to the oil pan.
It is an example of the type of development that defines high-level racing engine engineering. The improvement did not come from a larger carburetor, more displacement or a radical new cylinder head. It came from reducing losses inside the engine and improving the environment in which the rotating assembly and ring package operated.
Those lessons remain relevant today: horsepower can be found not only by producing more combustion pressure, but also by reducing the amount of power the engine consumes internally.
From Road America to 12,000-Horsepower Top Fuel Engines
Today, ProMotor Engines' workload spans an unusually broad range of racing applications.
At one end are road racing and vintage engines, including NASCAR-derived pushrod V8s that continue to compete years after their original professional racing careers ended. Borem discussed working with Joe Nemechek and supporting former NASCAR Cup cars now competing in historic racing, including a recent group of approximately 15 engines that went to Le Mans with historic stock cars.
At the opposite extreme is NHRA Top Fuel.
ProMotor handles Top Fuel short-block work along with block and cylinder head services, including work associated with Rick Ware Racing's nitro program.
The maintenance cycle bears little resemblance to endurance-oriented road racing.
After racing, short blocks return to the shop where run counts are reviewed and components are systematically inspected. Crankshafts are Magnafluxed for cracks, blocks and sleeves are inspected and repaired, main bearing alignment is checked, damaged components are welded when possible, and parts are re-machined for another service cycle.
ProMotor's capabilities include dedicated machining, cylinder head and CNC resources, allowing the company not only to build engines but also to recover expensive racing components that might otherwise be discarded.
During the webinar, Castello shared a comment from a racer who said ProMotor had successfully repaired a cylinder head that its manufacturer had retained for a year and ultimately declared unrepairable.
For Borem, that capability comes back to experienced people and knowing what can realistically be saved.
The Dyno Is the Final Quality-Control Station
Despite the enormous differences between a Trans Am V8 and a nitromethane-burning Top Fuel engine, Borem sees the fundamentals of reliable horsepower in surprisingly simple terms.
It begins with quality components, correct machining, disciplined procedures and meticulous assembly.
His description of internal engine clearance summarized the philosophy particularly well: everything inside a racing engine operates extremely close together, but those components cannot be allowed to interfere with one another.
Valve spring clearance is one example. At maximum valve lift, the spring operates near coil bind, but the coils still must maintain the intended clearance. Similar precision applies throughout the engine.
Clearances, machining processes and assembly procedures therefore become just as important as the parts themselves.
Once assembly is complete, the engine is blueprinted, checked and sent to the dyno.
With the exception of the nitro engines, ProMotor dyno tests every complete engine it builds.
The dyno isn't simply a tool for generating an impressive horsepower number. It is the final verification that the engine performs as intended before being installed in the race car.
“The dyno is kind of our best friend,” Borem said.
In Top Fuel, the racetrack effectively becomes the dyno. With roughly 12,000 horsepower involved, engine output cannot be separated from clutch application, traction and the rest of the vehicle. Making power is only part of the problem; successfully applying it is the larger engineering exercise.
Decades of Knowledge Behind Every Engine
Technology was only part of Borem's message.
ProMotor's capabilities are supported by an unusual depth of institutional experience. Borem noted that one of the company's engine assemblers has been with the organization since 1977, while his son has worked there for approximately 20 years.
That experience becomes increasingly important as the racing industry faces a shortage of skilled engine builders and machinists.
Borem sees opportunities across road racing, circle track, drag racing, vintage competition and grassroots motorsports precisely because many racers can no longer rely on the local machine shop or engine builder that once supported their programs.
ProMotor is also working to transfer that knowledge to another generation, including hiring graduates from technical training programs and investing the time required to develop their skills.
For Borem, technical ability and relationships ultimately reinforce one another.
“We can't do what we do without good relationships with people,” he said.
Reliable Horsepower Comes From the Entire Process
The discussion ultimately demonstrated why the definition of a “race engine” changes dramatically depending on the application.
A sealed TA2 engine must provide tightly controlled, repeatable performance over multiple events. A high-output Trans Am engine may be tuned around the torque and horsepower requirements of an individual track. A NASCAR-derived vintage engine combines proven architecture with modern preparation. A Top Fuel short block must survive one of the most violent operating environments in motorsports before being inspected, repaired and prepared to do it again.
The engineering principles connecting them are remarkably consistent.
Start with quality parts. Machine them accurately. Establish the correct clearances. Control ring seal and friction. Optimize airflow and combustion. Blueprint the assembly. Verify it on the dyno. Understand the duty cycle. And, perhaps most importantly, don't promise a customer maximum horsepower without explaining what that additional performance will cost in durability.
For ProMotor Engines, the objective is not simply finding horsepower.
It is building the right horsepower for the racer, the engine and the job it has to do.
For more information, watch the full webinar here.
