In this video, we put theory to the test and dive into the real reason why diesel trucks smoke, with hard dyno data to back it up. This is part two of our deep dive into diesel combustion, where we explore the relationship between air-fuel ratio (AFR), Lambda values, exhaust gas temperature (EGT), smoke output, and horsepower. If you caught our recent podcast episode where we explained the science behind diesel smoke, tuning, and Lambda strategy, this is the live-action follow-up where you’ll see how it all plays out on the rollers. We strap two high-performance trucks to the dyno, a P-pump mechanical build and a common rail monster, and walk through multiple fuel trims and tune-ups to find out exactly when smoke starts, how it impacts power, and what role nitrous plays in cleaning things up while keeping horsepower high.
From a rich 0.95 Lambda to an ultra-lean 1.5+ Lambda, we walk through the curve of power vs cleanliness and what happens when you chase one at the expense of the other. You’ll see real-world power loss as we lean the fuel out, EGT changes, boost behavior, and whether running cleaner actually makes sense in a racing application. We even show how much horsepower you can gain (and how much heat you can drop) with nitrous on a lean mid-power tune. Along the way, we cracked a block, blew a radiator hose, and still gathered some of the most valuable tuning data we’ve ever seen. This isn’t theory, it’s real-world performance testing with real trucks and real consequences.
If you haven’t yet watched or listened to the original podcast, “Why Do Diesels Smoke?” make sure to check it out. That episode breaks down the technical foundation of what you’re seeing in this video: from injection timing and fuel atomization to why modern common rails stay cleaner at the same AFR than older mechanical trucks. We’re not advocating smoke on the street, this is about understanding why it happens, how it affects performance, and what it takes to build a clean, powerful, and reliable diesel setup.
Whether you’re tuning a max-effort drag truck, dialing in your spool-up for sled pulling, or just curious how diesel tuning actually works at a high level, this is a must-watch. You’ll walk away with a better understanding of Lambda tuning, AFR strategy, and the real-world compromises between horsepower, heat, and emissions. Stick around, subscribe for more diesel tech content, and let us know in the comments what topics you want to see next on the dyno.
This dyno session started with a question — Why do diesels smoke?
We answered it with data. Now go deep with the full theory behind it.
🎧 Watch the full podcast here: https://youtu.be/kHxpHzEr3kU
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