If you have ever questioned whether custom tuning is worth the time and money compared to the stock tunes that come loaded in your truck, this video is going to answer it with real testing and real results. We took our VP44-powered 24-valve Cummins, nicknamed Willard, and put it through a full round of street driving and dyno testing to show you exactly what happens when you move from stock QuadZilla box tunes to custom written tunes that are tailored to your truck’s setup. No hype, no guessing, just straight results from the street and the rollers.
This truck has already seen a few upgrades in its build. We’ve added fueling improvements through the Quad module, we’ve swapped out the turbo for our Aggressor 60/64, and we have a solid transmission under it to hold the power. In our last video, we asked you guys whether we should throw injectors in first or test custom tuning first, and the overwhelming answer was tuning. So that’s what we did here. The goal was to see if tuning alone could improve throttle response, spool up, drivability, and ultimately power, even with stock injectors still in place.
On the street, the differences were noticeable right away. With the box tunes, drivability wasn’t bad, but there was a delay in throttle response and the boost-limited fueling created lag you could feel every time you tried to get moving. When we switched over to the custom files, the truck picked up pep. It felt sharper off the line, throttle response improved, and it carried itself better through the gears. It wasn’t a night-and-day transformation, but when you drive these trucks every day you notice the difference between “good enough” and “dialed in.” That’s what custom tuning gives you.
Then we put it to the real test on the dyno. With the QuadZilla box tune, Willard made 351 horsepower and 810 lb-ft of torque. Respectable numbers for the setup, but when we loaded in Griff’s custom street tune, the truck laid down 375 horsepower and 827 lb-ft of torque. That’s a solid 24 horsepower and 17 lb-ft gain just from the tuning change. The dyno graph told the same story we felt on the street, quicker spool up, stronger torque curve, and cleaner fueling all the way through. The truck responded sooner, carried power better, and stayed smooth without haze or smoke.
This proves a simple but important point: stock or box tuning can only take you so far. Those files are written to be “one size fits all” with stock parts, but once you start changing turbos, adding injectors, or chasing real performance, they no longer match what your truck needs. Custom tuning fills that gap. It lets you get the most out of your setup while keeping it clean, reliable, and fun to drive. Whether you’re towing heavy loads, daily driving, or just wanting more out of your Cummins, a proper tune makes a world of difference.
Our goal with this truck is 500 horsepower, and with injectors going in next, we’re getting close. But this video proves that even with stock injectors, the right tune can wake up a build. If you’re running a VP44 truck or any diesel that’s been upgraded past stock, custom tuning is not just worth it, it’s a must.
Make sure you subscribe to Power Driven Diesel, drop a comment on what you want to see next, and follow along as we continue building Willard into a true powerhouse. Injectors are up next, and that’s when the real fun begins.
Power Driven Diesel is a specialty performance shop engaged in the engineering and development of high-performance turbo diesel technologies.
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