Building A Twin-Turbo Supercharged Monster Truck Engine With Banks

When it comes to insane turbocharged combinations and technology, Gale Banks of Banks Power is regarded as a guru. So when he puts together a series of videos on YouTube detailing the development of an insane diesel engine project to power a monster truck, we shut up and watch.

Currently at 17 months and counting since the first video in the series was released, this is no simple engine build, but rather a complete reengineering of a Duramax L5P from a capable 6.6-liter powerplant into a high-RPM, mega-boosted 7.0-liter monster — pun intended — destined for the “Monster Mutt” Monster Jam team.

While the long block itself isn’t discussed much, we can deduce that one of Banks billet “big pin” stroker crankshafts resides inside the factory block. An insane dry-sump oiling system features five scavenge stages and two pressure stages in order to provide all the oil this beast will need.

However, the centerpiece of this video is the induction setup: twin-turbochargers feeding a Whipple twin-screw supercharger. More than just compound power-adders, the engineering that has gone into the system is mindblowing for us mere mortals, and just another day at the office for Gale Banks.

When One Isn’t Enough

Part of the reason this has been such a lengthy process is that getting the supercharger portion of the equation right has been a challenge. Starting with traditional 8-71 and 10-71 Roots blowers, Banks made the switch to a 5.0-liter Whipple twin-screw supercharger after killing the 10-71 on the dyno.

After rigorously testing the Whipple at 5,000 engine-RPM continuously (with the process documented in video #7) Banks reveals that the 7,500 rpm the blower is spinning is only half of the blower’s capability. While satisfied with the Whipple’s performance, Banks wasn’t satisfied with the blown Duramax’s numbers in general.

“I wasn’t happy with the 666 horsepower we got. I want more,” says Gale Banks. “When we tested the Monster Mutt, we found out that to be competitive, you need 1,300 to 1,400 horsepower in a monster truck. We wanted to do a diesel version of a monster truck engine that has the throttle response that the 540 cubic-inch blown alcohol big block Chevy.”

While turbochargers seem to make everything better, one thing they aren’t known for is throttle response. So Banks’ idea was to keep the supercharger for the throttle response and add turbos for more power. “I’m looking to be putting boost pressure into the manifold at idle. The turbos are just kind of loafing around at idle, but the supercharger is putting pressure into the manifold,” explains Banks.

While Banks started out with traditional 8-71 and 10-71 Roots superchargers, he eventually moved to a Whipple 5.0-liter twin-screw supercharger. With the current gearing, the supercharger is good to 10,000 engine RPM. While that might sound ludicrous in a diesel application, Banks plans on approaching that threshold before development is done.

Adding Twins on Top

With the supercharger, Banks ran a set of zoomie headers on the dyno, but for the turbos, a much more robust manifold is needed. “It all starts with the Banks hi-temp cast and ported exhaust manifolds, says Banks. “A lot of guys will get very focused in on what they are doing to get air into the engine. Once it’s in the cylinder and runs through the combustion process, now you have to get it out of there.”

“A poor exhaust system won’t scavenge the cylinders to the greatest extent possible, and then there are exhaust gasses that remain in the cylinder when you go to fill it again, which then compromises everything you are doing on the intake side.”

Banks starts by opening up the stock exhaust ports and upsizing the exhaust valves in the cylinder heads, then adding the new L5P variant of his cast exhaust manifolds. Besides the larger runner ports, the manifold outlet is larger as well, sized specifically for big-power applications.

A pair of Precision 6870 ball-bearing turbos with 1.05 A/R housings will provide a ton of the engine’s horsepower by feeding into (or bypassing, as the strategy dictates) the Whipple supercharger.

“The factory manifold outlet is about 1-3/4 inches, and the Banks manifold is 2-1/8 inches,” Banks explains. “That allows you to run a 2.25-inch OD exhaust tube with a .065 wall-thickness and have it match up. But in this application, we’re running a 2.5- inch OD tube with a .150 inch-wall-thickness, so it’s a 2.200-inch ID with a 3.0-inch centerline radius bend for our up-pipe, which is larger than any up-pipe on the market.”

All that flow is needed to drive the twin Precision 6870 ball-bearing turbochargers Banks has chosen for the build. “These have a 2618 forged-aluminum compressor wheel, and a 713C Inconel turbine wheel. The dual ceramic ball bearings will help increase response time, too,” says Banks.

“The housings have a 1.05 A/R; this is a response program, with short durations at WOT. We’ll probably run one of our bigass air filters on it and dual mass-airflow sensors, so there’s no pressure drop before the compressor.”

On the left, you can see the air-to-water charge-air cooler on the inlet of the Whipple supercharger. The 60mm wastegate on the cooler's inlet allows boost from the turbochargers to bypass the cooler (and the supercharger itself) and feed directly into the post-blower manifold (right), and then through the large charge-air cooler and into the engine.

Where things start to get really interesting is after the turbochargers outlets. The 3.0-inch tubing feeds into an air-to-water cooler, with a 60mm wastegate on the inlet side of the cooler, in order to be able to divert airflow around the supercharger.

“Once the turbos take off, I fully expect that the supercharger will need some bypass around it. I don’t know that for sure, but I’m providing for it,” Banks elaborates. “We’ll be able to vary the wastegate’s opening based on the pressure difference at the inlet of the blower and the outlet of the blower.

Air that isn’t diverted will exit the cooler and feed directly into the Whipple’s inlet. From there, the compressed air will join any diverted air below the supercharger, and everything will go through another air-to-water charge-air cooler before being ingested by the engine.

Yes, that’s a blow-off valve being used in its traditional role. “People will say ‘But it’s a diesel, there’s no throttle body’,” says Banks. “I’m telling you, the minute you turn off the fuel, the RPM will drop very rapidly and you have the same issues [stalling the compressors] as you do with a throttle. It’s not quite as bad but you can run the compressors into surge.”

As if this whole project isn’t interesting enough, Banks has had to upgrade his dyno just to test this whole combination. “We’re working with Froude on a new absorber and control system for the dyno that will allow steady-state, full-load runs to 3,600 lb-ft and 2,000 horsepower,” says Banks.

“Flash readings will probably be 3,500 to 4,000 horsepower and 5000 lb-ft of torque. I’m loving it! We’re going to find out how far we can buzz a diesel here in this whole process. Our ECU is done at 8,000 rpm our dyno is done at 9,000 rpm.”

While it’s a bit of a time investment, we strongly suggest you go back and watch parts one through nine of the series as well. This project is so much more than just a simple engine build with dual power-adders (or three, technically) to make tons of power. This project showcases some pretty interesting theories in practice, as well as highlights just how ingenious Gale Banks really is when it comes to forced induction, as well as making so much power that Banks needed a bigger dyno.

We can’t wait to see and hear this thing running on the dyno. With Banks’ power estimates as well as his desire to spin the combination to the moon, it should be a sight to behold.

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About the author

Greg Acosta

Greg has spent fifteen years and counting in automotive publishing, with most of his work having a very technical focus. Always interested in how things work, he enjoys sharing his passion for automotive technology with the reader.
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