The whole job was simple on paper: hold the same torque at higher rpm and the horsepower number takes care of itself. The hard part was getting there without leaning on more boost or blowing past the limits we set for cylinder pressure, turbine temperature, compressor discharge temperature, turbo speed, and injection duration. The key was the Banks-spec Comp camshaft. At higher rpm, the valve is open for less actual clock time even if the cam card duration number stays the same. That shorter open time hurts cylinder fill. We increased duration to recover that lost valve-open time at 3,809 rpm, which let the engine keep filling the cylinders well enough to carry torque where the stock cam would fall off. That cam change also let the rest of the system work better. The larger Precision turbo improved boost-to-backpressure ratio and engine scavenge, so the cylinders emptied and refilled more effectively. Even with slightly lower manifold air density and nearly the same boost pressure, cylinder fill improved and mass airflow climbed from 94.9 to 104.3 lb/min. That is how this stock-internal L5P went from 912 hp to 1,004 hp. We verified the whole combination with Banks iDash data logging. When you can see air density, pressure ratio, temperature, scavenge, and cylinder fill in real time, you stop guessing and start understanding why the engine made the power.
After more than a year of trying to break a bone-stock Duramax L5P, the team pushed the engine to a new target: 1,000 horsepower on untouched stock internals. The truck had already received major supporting upgrades, including an improved air intake, a Precision turbocharger, a Banks 5-inch exhaust, an S&S high-pressure pump, S&S injectors, and, most recently, a Banks-spec Comp camshaft. The objective for this session was simple but risky: make four-digit power without destroying the engine in the process.
The baseline for the effort was a previous 912-horsepower run at 3,447 rpm. From that starting point, the plan was to hold roughly the same torque at a higher engine speed. If the engine could maintain 1,389 lb-ft at 3,800 rpm, the result would be about 1,005 horsepower. That became the engineering target for the entire combination.
Before making the pull, the team established a set of red lines based on both engine durability and component limits. Maximum cylinder pressure was set at 260 bar, even though that is already far above the engine's original design level of 183 bar. Exhaust gas temperature at the turbine inlet was limited to 1,650°F. Compressor discharge temperature was capped at about 480°F. The air-fuel ratio target was no richer than 16.2:1, turbo shaft speed was limited to 125,000 rpm, and main injection duration was held to a personal limit of 40 degrees of crank angle. Injection timing was set at 23 degrees before top dead center, with a nominal on-time of 1,750 microseconds at 3,800 rpm.
Fuel supply details mattered because the truck had moved away from the stock Denso system. The setup used a Bosch-based S&S 12 mm stroker CP3 high-pressure pump, and unlike the earlier Denso arrangement that required much higher lift-pump pressure, the Bosch-based S&S pump was run at about 15 psi lift-pump pressure. Rail pressure was increased from 2,200 bar to 2,400 bar to support the higher power level while keeping injection duration under control.
To move from 912 horsepower to the 1,000-horsepower target, several key components were upgraded. The stock L5P camshaft was replaced with a Banks-spec cam developed with Comp Cams. The previous Precision 7675 turbocharger was replaced by a custom Precision 8085 unit. The boost-control system was also revised from a 3-port arrangement to a 4-port TurboSmart controller. On the fuel side, the stock pump was replaced by the S&S 12 mm stroker CP3, and the earlier 50% over S&S injectors were replaced with S&S 100% over injectors.
These changes were intended to support more airflow and fuel at higher rpm without changing the stock heads, stock valve gear, or the stock rotating assembly. That point was central to the test: despite the extensive bolt-on system changes, everything inside the engine remained factory except the camshaft.
The camshaft was the foundation of the entire strategy because the team needed to make the same torque at a higher engine speed. Gale explained that cam cards do not directly tell you valve open time in milliseconds; they describe valve events in degrees of crankshaft rotation at a given tappet or valve lift. Actual valve open time changes with rpm. For a fixed duration in crank degrees, the valve is open for less clock time as engine speed rises.
On the stock L5P cam, intake duration at 0.050-inch tappet lift was 155 degrees and exhaust duration was 164 to 166 degrees. At 3,447 rpm, that intake duration translated to about 7.5 milliseconds of valve open time. At 3,809 rpm, the same duration would only provide about 6.8 milliseconds. That loss of roughly 0.7 millisecond, or 10.3%, had to be recovered if the engine was going to maintain the same cylinder filling and therefore the same torque at the higher rpm.
Using that logic, the intake duration would need to increase from 155 degrees to about 171 degrees, and the exhaust duration from 164 degrees to about 181 degrees, just to match the earlier valve-event clock time. Gale noted that the final camshaft durations ended up larger than those illustrative numbers, but the key point remained the same: the camshaft had to restore valve open time lost to higher rpm. That increase in duration enabled the rest of the system to work.
The engine's power increase came not from making each combustion event dramatically stronger, but from maintaining the same strength of each event while increasing how often those events occurred. At 3,447 rpm, the V8 produced about 230 power pulses per second. At 3,809 rpm, that rose to 254 power pulses per second, an increase of about 10.5%. If each pulse could be kept equivalent to the earlier 912-horsepower condition, total power would rise accordingly.
That is exactly what the team set out to do. The camshaft, turbocharger, fuel system, and charge-air system were all chosen to preserve cylinder filling and torque at the higher engine speed. In the final result, the truck produced 1,004 horsepower at 3,809 rpm while essentially holding the target torque. For Gale, that validated the entire approach: maintain the quality of each power pulse, then increase the number of pulses per second.
The environmental conditions were not favorable. Ambient pressure was essentially identical between the 912-horsepower and 1,004-horsepower runs, but ambient temperature rose from a cooler condition to 89°F on the higher-power test. That reduced ambient air density from 72.5 lb per 1,000 cubic feet to 69.8 lb per 1,000 cubic feet. Even so, airflow demand increased from 1,309 to 1,494 cfm because higher horsepower at a similar air-fuel ratio requires more air.
The intake system used two large Banks L5P filters in parallel. Pressure drop through the intake increased only slightly, from 0.43 psi to 0.49 psi, while air temperature gain through the intake remained minimal at roughly 1 to 1.5 degrees. The intake system did impose a small density loss, costing about 7 horsepower at 912 hp and about 9 horsepower at 1,004 hp, or roughly 0.8% to 0.9% of total output. Gale noted that with Ram-Air, those values could become positive rather than negative.
The move from the Precision 7675 to the custom Precision 8085 was not about raising boost dramatically. In fact, compressor pressure gain was slightly lower on the 1,004-horsepower run, dropping from 47.1 psi to 46.4 psi, because the team was intentionally trying to control compressor discharge temperature. Compressor outlet temperature rose from 458°F to 489°F, slightly above the intended 480°F limit, partly because of the hotter day. Compressor efficiency changed from 73.1% to 71.9%, still a respectable figure for this operating range.
Despite the lower density produced by the hotter compressor discharge, mass airflow increased from 94.9 lb/min to 104.3 lb/min. That increase in mass flow was the real gain. The turbocharger's contribution to horsepower rose from 343 to 370 horsepower-equivalent, even though density was down, because the larger turbo supported more total airflow.
Downstream of the turbo, the truck used a Banks prototype air-to-liquid charge air cooler. Pressure loss across the cooler improved slightly, from 2.3 psi to 2.1 psi, right at Gale's preferred limit of about 2 psi. Temperature reduction across the cooler increased from 368°F to 387°F, and the resulting air-density gain remained nearly unchanged at about 108.4 versus 107.0 lb per 1,000 cubic feet. Effectiveness improved from 95.5% to 96.9%, and charge air cooler efficiency rose from 83% to 86%. Gale emphasized that the charge air cooler was contributing as much horsepower as the turbocharger itself, with horsepower-equivalent gains of 345 and 389.
Looking at the entire boost system from ambient air to the intake manifold, boost air density dropped from 213 to 206.1 lb per 1,000 cubic feet, and manifold pressure slipped slightly from 44.4 to 43.8 psi. Total system pressure ratio changed only marginally, from 4.08 to 4.04. Even so, the system remained optimized for sustained operation rather than brief peak numbers. Gale stressed that many impressive compressor-map pressure ratios exist only momentarily, whereas this program was built around repeatable, sustained running.
The larger turbo and revised system improved the relationship between compressor work and turbine backpressure. Booster backpressure ratio moved from negative 1.4% to positive 12.5%, meaning the new setup reduced the penalty of turbine-side restriction relative to compressor-side pressure gain. Engine scavenge ratio also improved substantially, from negative 3.4% to positive 8.7%, indicating that intake manifold pressure had moved from being lower than exhaust manifold pressure to being favorably higher.
That improvement showed up directly in cylinder fill. Cylinder fill percentage increased from 82.4% to 85.2%. Although manifold air density was lower, the engine filled the cylinders more effectively, so actual cylinder air density remained nearly unchanged at the higher rpm. With similar cylinder air density but more engine cycles per minute, displaced airflow rose and mass airflow increased from 94.9 to 104.3 lb/min. That is why torque stayed essentially constant while horsepower climbed.
The final dyno pull produced 1,004 horsepower, surpassing the original four-digit goal while the stock-bottom-end L5P survived. The measured values did brush past several red lines: cylinder pressure reached 262 bar, turbine inlet temperature hit 1,672°F, and compressor discharge temperature touched 489°F. However, turbo shaft speed remained comfortable at 107,000 rpm, and main injection duration stayed within the intended limit at 37.4 degrees of crank angle.
For Gale, the result was a tribute both to the Duramax platform and to the engineering path used to get there. The stock-internal L5P handled a level of cylinder pressure and airflow far beyond its original design target, and the combination of camshaft timing, larger turbo sizing, improved boost control, increased rail pressure, and larger injectors achieved the intended outcome: nearly identical torque at higher rpm. In practical terms, that meant more power pulses per second without sacrificing the strength of each pulse.
The test also clarified what made the combination work. The camshaft restored valve-event clock time at elevated rpm. The larger turbo improved flow range and turbine matching. The charge air cooler preserved density with very high effectiveness. Together, those changes improved scavenging and cylinder fill enough to offset lower ambient and manifold air density. The engine made 1,004 horsepower not by brute-force boost alone, but by sustaining airflow quality and combustion conditions at a higher engine speed. Gale closed by noting that the engine had not yet failed, but eventually it would. The open question was what the next step should be: compounds, water-meth, or nitrous.