To VGT or Not to VGT, that is the question...
Upgrading your truck can be an exciting but overwhelming task, especially when it comes to choosing the right turbo. With options ranging from bigger turbos, compound setups, to Variable Geometry Turbos (VGT) and non-VGT swap kits, it can be tough to decide which is best for your needs. One common dilemma is whether to swap out a VGT for a non-VGT. While this swap can offer certain benefits, it also comes with some important considerations, the biggest being legality. To help clear things up, I reached out to the turbo experts at KC Turbos.
“The VGT vs. non-VGT debate is one we’ve been addressing for years,” says Cameron Lewis of KC Turbos. “In our experience, a properly functioning VGT spools faster and generates more power across the power band compared to a non-VGT in setups under 650 horsepower on a 6.0 and 6.7-liter Power Stroke. The larger the setup, the more a non-VGT can shine. Smaller setups, however, benefit greatly from a VGT. Ultimately, the decision often comes down to personal preference for sound, feel, and driving style. It's hard to believe that a non-VGT can spool faster than a VGT, as our tests consistently show otherwise.”
For the last decade, diesel trucks from the factory have been equipped with Variable Geometry Turbochargers. Older trucks used fixed vane turbos. What’s the difference? Let's break it down.
A VGT can adjust the path of exhaust gases to change their impact on the turbine wheel. It uses movable teardrop-shaped vanes around the turbine impeller, controlled by a rotating unison ring. At low RPM, the vanes stay mostly closed, increasing exhaust gas velocity to spool the turbo faster, reducing lag. At higher RPMs, the vanes open to allow more exhaust gas flow, avoiding restrictions that could reduce power. This adaptability makes VGTs a great option for most truck owners.
The ability to adjust the turbo’s A/R (area over radius) ratio as conditions change is a key advantage of VGTs. A smaller A/R spools the turbo faster but limits maximum output, while a larger A/R takes longer to spool but allows for greater power. VGTs offer the best of both worlds by altering the effective housing size as needed.
However, VGTs have their downsides. The internal vanes can get stuck due to carbon buildup, which can stress the electronic actuator and eventually cause it to fail. Symptoms of this issue include sluggish acceleration, low power, and a non-functioning exhaust brake. Fixing it requires disassembling and cleaning the turbo, which is no small task.
Non-VGT turbos, on the other hand, have a simpler design with no variable parts. This makes them more reliable and longer-lasting. However, without variable geometry, the turbo’s performance depends solely on exhaust gas volume, leading to trade-offs. A small A/R turbo spools quickly at low RPM but chokes at high RPM. Conversely, a large A/R turbo provides more power at high RPM but suffers from turbo lag and a higher boost threshold.
Choosing the right non-VGT turbo comes down to selecting the appropriate A/R ratio for your driving needs. There’s no one-size-fits-all solution, so it’s best to consult with a turbo manufacturer to find the right fit for your specific requirements.
Back to the VGT vs. non-VGT swap question. “For setups exceeding 650 horsepower, the low-end torque advantage of a VGT diminishes,” explains Cameron. “At this point, a single non-VGT or compound setup becomes more beneficial. For example, our built 6.4-liter truck with compound turbos makes 1,000 rear-wheel horsepower and is still great for towing because of its low-end power. Achieving that with a big single non-VGT would make towing difficult.”
Cameron emphasizes that for towing or daily driving, sticking with a VGT is usually the best choice. For those seeking both high power and towing capability, a compound setup with a VGT and a non-VGT provides the best of both worlds.
“It’s all about managing expectations for your truck,” Cameron concludes. “If you’re chasing big power for a purpose-built truck, a non-VGT can make sense. But for most people who enjoy the low-end power for daily driving or towing, a VGT is ideal.”
Lastly, consider the legal implications. The EPA regulates turbo modifications, and swapping to a non-emissions-compliant part could get you in trouble. Always check the regulations before making a change.
In summary, whether a VGT or non-VGT is right for you depends on your specific needs and goals. Consult with turbo experts, be honest about your plans, and ensure you’re informed about the legal aspects.
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