EDITOR’S NOTE
TRACKING THE NEW SINGLE-TURBO TREND
Up until roughly two years ago traditional two-turbo compounds were the hottest way to go. All the big dogs were running them and everyone else wished they were. Last year we started seeing a lot more triples, still a compound design but with three turbos instead of two. Those made great power, just like their two-turbo brethren did. But lately I’ve been seeing a different trend in the big horsepower trucks: They’re running singles. One turbo. Just like what comes stock on your truck. Nothing fancy. But they’re making huge and reliable power with them. Recently I’ve had a few people ask me how this is possible and why it makes sense to run a single, so I’ll explain why.
High RPM Saves Parts
To understand part of why a single makes sense you need to know this: Assuming you have the correct supporting mods (upgraded valve springs being a perfect example) high rpm saves parts. There’s more to it than this, but think about waterskiing: You need some speed to skip across the water and without that speed the water will “grab” you and you’ll fall or sink. Same sorta idea with engines, transmissions, transfer cases, and so on. At higher rpm the parts don’t see the stress they do at low rpm. Parts skip off each other better instead of digging into one another and causing damage. Plus at high rpm the parts already have momentum; adding more power up top will be kinder to the rods compared to adding power down low.
Compounds
Many people call two-turbo compound turbo systems “twins.” While we all know what this means, it is not the correct name. “Twins” are two identical turbos feeding the engine on their own. Another correct phrase for this setup would be “Parallel Turbos.” Compounds are one turbo blowing into another. So you get the first stage of compression via the large turbo (or the Atmospheric Turbo), then that pressurized air is fed into the smaller turbo (the High Pressure Turbo) for its second round of compression before it’s pumped into the engine. So this system essentially compounds the air charge, hence the name. Traditional triples are three of the same or roughly the same size turbos, two blowing into the third. There are multiple reasons behind this technology—more air obviously—but a big consideration has to do with cost. Buying three small frame turbos is generally cheaper than buying one large and one small frame turbo. With a compound system the benefit is you get power down low in the rev range as well as up top. Turbo lag is extremely minimal for smaller systems.
Single Turbo
A single turbo setup is fairly selfexplanatory. One turbo feeding the engine, only one stage of compression. For most of us, a small single turbo for our daily drivers is all we need. Sure, standard non-vgt turbos have some lag, but if the turbo is kept small enough it’s minimal and doesn’t affect drivability. On the flip side, larger turbos will have more lag and take longer to create boost. So when running a single fixed-ar turbo the charger really needs to be matched to how the truck is going to be used. Today’s Variable Geometry Turbos (VGT) offer the best of both worlds. They spool almost instantly but also open up for high-rpm power. The negative here is they are known to create significant backpressure and they have a limited lifespan compared to non-vgts.
Why Singles Now?
Well, they’re simple, light, reliable and for most of the race applications they help keep parts alive. Less moving parts to tune and deal with—plus, remember the rpm discussion earlier? Using one massive turbo means the engine needs to be high in its rpm range to spool the turbo, which means it’s not making significant power until the engine is really spinning. So that means a significantly lower chance for damage to internal parts.
I’m thinking we diesel performance enthusiasts have reached a point after pushing the envelope so hard over the last several years that we’re finally realizing things don’t have to be so over-the-top to work well. Jeremy Wagler is making more consistent and usable power with the DX500 Shop Truck after pulling the turbos off it; Shawn Baca pulled his triples in favor of a big single and made the best pass Master Shredder has ever done; Rawlings Barnes and his World’s Fastest Power Stroke was originally set up with triples but is now a single. The trend is growing.