Insights for Diesel Owners: the Pros and Cons of Turbochargers

Turbo cutaway

Last week we looked at a triple turbo diesel setup that was quite intriguing and incredibly powerful. In that article we looked at how turbochargers can improve horsepower and torque. But we never examined the downside of turbos. Are turbochargers always beneficial? Is there a downside to turbos that people can neglect to consider? 

Turbos have generally been add-ons that improve engine efficiency and performance. In recent years more and more vehicles have been fitted with turbochargers from the getgo.

The way a turbo works is like this: hot exhaust gasses spin the turbine that is connected to another turbine which sucks air in and compresses it into the engine. It is this compression that provides the engine with extra power. The more air you can get into the engine, the more fuel can be added for more power.

We're fairly well acquainted with the benefits of turbochargers. Extra power is primary. Unlike superchargers, there is no engine drain because the power comes from hot, expanding gases coming out of the engine already. In addition, turbos aren't affected by the thinner atmosphere of higher altitudes. Furthermore, turbos provide better fuel economy, so they are a win-win on several fronts.

What's the downside then?

The first is heat. Turbos are powered by hot exhaust gases and they get hot, hot hot. How hot? Hotter than molten lava! When pushed to its limits for a continuous amount of time the turbo can start glowing red. For this reason racers have vents to get air circulation flowing through the engine bay. 

The second is friction and heat in the turbine itself. Think about this for a second. Your engine revs at 2,000 rpm when cruising. Your turbo's turbine can reach speeds of more than 280,000 rpm. When I wrote, "Think about this for a second," it was to make you think about this: in one second that turbine will spin as many as 4,666 times. Try wrapping your head around that... more than 4500 times a second. That's a lot of friction there if the lubrication is insufficient.

This turbocharger bearing system is lubricated by the oil from the engine which is fed under pressure into the bearing housing. The oil is both lubricant and coolant. This is one more reason that the engine oil you select meets specifications.

Another disadvantage with turbochargers that doesn't get talked about much is "turbo lag." At times, when conditions are right (or wrong), there will be a delay between the moment you stomp on the pedal and the moment you actually feel power. This is turbo lag. 

At low speeds there aren't a lot of exhaust gases passing through the turbo, "so when you demand power from the engine, the turbocharger turbine needs time to start spinning at an optimal speed. The effects of this can be reduced by downshifting to a lower gear." Astute drivers will still notice the split delay at times.

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Because of their benefits, turbochargers have almost universally become stock equipment on diesel pickups and will be around for years to come. It's useful, however, to be aware of their shortcomings.

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Sources 

What Is a Turbocharger and How Does It Work

Eight Things About Turbochargers You (Probably) Never Knew

This Triple Turbo Diesel Setup Is Not for the Faint of Heart

Triple in-engine 6.4L Ford

A turbo -- shorthand for turbocharger -- is a turbine-driven, forced induction device that increases an internal combustion engine's power output by forcing compresses air into the combustion chamber. By forcing more air and more fuel into the combustion chamber, it produces more energy. 

This concept of forced induction was conceived as early as the late 19th century by Gottlieb Daimler who patented the technique of using a gear-driven pump to force air into an internal combustion engine. That was in 1885! He had the right idea, and in the 21st century more power is being produced by means of turbo-diesel technology than he could ever have imagined.

Yesterday I came across a 2017 Diesel World article by Jason Sands about a three-turbo 6.4L Ford that cranks out 1,221 hp and a mind-blowing 2,532 lb-ft of torque. Just reading about it makes you want to catch your breath. It had been re-published on the Power Driven Diesel website because they were the team that did the work.

Sands begins by noting how much flexibility there is today with regard to diesel setups. It used to be that you had a choice between a single turbo and a compound two-turbo setup. "Today," he writes, 'there are virtually endless choices, from ball-bearing turbos to large but quick-spooling singles, to compound turbo setups that will support a vast amount of horsepower."

COMPOUND TRIPLE TURBOCHARGERS
Twin turbos have been around awhile, but sled-pullers have been running triple turbos and even quads for years. "It was only a matter of time before pickups followed suit." Here's why triple turbos have an advantage over two. It's not just because there are more of them. First, twin turbos need to make such massive amounts of horsepower that they can be hard to spool, and they make a dent in your wallet. "Instead of a 95 to 106mm turbo, the same amount of airflow can be provided by smaller frame 66 to 69mm turbochargers." In short, sometimes bigger isn't always better. And ultimately, you will have a better driving setup.

Got pipes?

The article then zeroes in on the setup for Power Driven Diesel's triple 6.4L setup. The client didn't just want power, he wanted 1200 horsepower, plus he wanted it to be a truck that could tow. PDD's owners --Will Terry and Todd Welch -- said they were up for it.

The rationale for selecting the BorgWarner turbos that they chose gets detailed, followed by all the decisions as regards how to mount them and run the piping. All of this is illustrated with photos. It was a pretty "wild creation" but they did it in two weeks. Then they tested it on the dyno. They nicknamed their beast "The Hulk." And yes, it delivered the goods.

THE COST
There's no free lunch in this realm. If you want to go big, you can expect to spend something more than a few pennies, but it doesn't have to cost an arm and a leg. Will Terry of PDD says if you want to do a triple setup it will cost between $5,000 and $10,000. This was 2017, and since we haven't shopped around for what's available today, don't take that as Gospel. Nevertheless, it will give you something to compare against.

You can read the full story, along with numerous photos, here:
Triple Threat: Building a Triple Turbo Setup