Follow along as we transform a stock 2015 GMC Sierra Denali into a 700HP daily driver that still passes emissions and tows 15,000 lbs reliably.
The Challenge: Big Power, Real-World Usability
Everyone wants a powerful diesel, but most "build" trucks end up unreliable or illegal. Our goal: Create a 700HP LML Duramax that remains emissions-legal, daily-driveable, and capable of serious towing. Here's how we did it.
The Starting Point
We began with a 2015 GMC Sierra 2500HD Denali with 85,000 km. Stock, the LML produces 397hp and 765 lb-ft. The truck was completely stock and well-maintained - the perfect canvas.
The Power Recipe
Tuning: We went with EFI Live by a reputable tuner who specializes in LML platforms. The tune optimizes injection timing and boost curves while maintaining proper emission system function. This alone added 80hp and 150 lb-ft.
Air Intake: Replaced the restrictive stock intake with a Banks Ram-Air. Cold air = denser air = more power. Simple but effective.
Exhaust: 5-inch turbo-back exhaust with DPF-back section. The stock exhaust is restrictive; this frees up significant power while keeping the DPF in place.
CP3 Conversion: The stock CP4.2 injection pump is a known failure point. We converted to a CP3 setup - more reliable and capable of supporting bigger injectors.
Injectors: Installed 60% over injectors. Combined with the CP3, this provides the fuel flow needed for serious power.
Turbo Upgrade: The stock turbo is surprisingly capable, but we upgraded to a 64mm drop-in replacement for better spool and top-end power.
The Results
On the dyno: 687hp and 1,247 lb-ft at the wheels. On the street: Seamless daily driving with stock-like manners until you put your foot down. The truck still passes AirCare, tows our 12,000 lb equipment trailer without breaking a sweat, and averages 19 MPG highway when driving normally.
Total Investment
Parts and labor came in around $18,000 CAD. That's significant, but you'd spend more than that on a lesser truck with similar performance. And this one is built to last.
Lessons Learned
Don't cheap out on tuning - it's the foundation of everything. Quality parts cost more but fail less. And always have a plan for emission compliance unless you're prepared for the consequences.
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Travis Andersson
Black Sky Diesel Team
Industry-leading diesel performance specialists based in Alberta. We share our hands-on expertise in diagnostics, tuning, and builds to help you get the most from your diesel engine.