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Turbos For The Street

Want to Make 1,000 HP? Add a Pair of Turbos

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Lund Racing: Pro Turbo Builders
Armed with some terminology, we started talking with some pro builders who are making incredible power with turbochargers as their ally.

Ken Bjonnes Lund Racing
For several months, we've followed the progress Ken Bjonnes has been making with Lund Racing's twin-turbo '11 Mustang, but we finally got to see it in person early this year at the NMRA's Spring Break Shootout at Bradenton Motorsports Park. Full details of this car can be found on page 10 of this issue, so we won't rehash them here. We did take the opportunity to talk with Ken at length about turbocharging, though.

"The biggest problem people have is they don't plan ahead," Ken says. "How much power do you want? How much room do you have? And how much money do you want to spend? Those are the first questions a person needs to address when planning a turbo build," he continued. "People tend to pay attention just to the turbo, but the turbo is one part of a complicated system."

When asked about the decision to install a single turbocharger or go with twin turbos, Ken says he prefers twin turbos on a V8 for street cars. Race cars that operate in a limited rpm range may benefit from a large, single turbocharger, but for a street engine, which needs to make power below the torque and horsepower peaks, a twin-turbo system will generally be more responsive and enjoyable to drive in traffic. In addition, Ken stressed the importance of getting air to the turbocharger efficiently, both on the inlet and exhaust sides. "The inlet size is important. The turbos need a large area of clean air [to draw from], and there shouldn't be a pressure drop anywhere in the inlet system." On the exhaust side, Ken likes to see as simple of a header as possible directing exhaust into the turbine. "Look at it this way, would anyone put five 90-degree bends on their cold-air intake?"

Lastly, Lund Racing and all the pros we talked with emphasized quality wastegates and bypass valves as critical to controlling boost. Cheap parts can be inconstant, and you can end up overspeeding the turbocharger or creating a situation where boost pressure rises above the bypass valve's rated limit. Boost creep, as this is known, can kill your engine in a hurry, especially if you're pushing the limits of your parts already. Where you place the wastegates also affects how efficiently and accurately they operate. Ken likes to place them close to the turbochargers, and if there's a bend at the pipe going into the turbocharger, the top of that bend is the ideal placement. This is where exhaust pressure will be the highest between the engine and turbocharger, so placing the wastegate there allows the most accurate control of boost.

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