Building a 236-bhp, Turbocharged Testastretta V-twin
Ducati’s extroverted Diavel already tends toward excess in terms of style, horsepower, and, of course, acceleration. With a tuned-for-torque version of the superbike-derived Testastretta V-twin mounted in a long, low, dragstrip-ready chassis, the Diavel delivers fast-forward acceleration that few motorcycles—production or otherwise—can as easily match. For a certain breed of two-wheeled extremists, however, even too much isn’t enough. Chad Wells, the builder of this turbocharged Diavel, is one of those guys.
Predictably, this isn’t Wells’ first turbo bike. “I had already built a Hayabusa with a Stage 1 turbo kit that made decent numbers,” he says. “That was cool, but everybody has one.” Working as service manager at Commonwealth Motorcycles in Louisville, KY, Wells had plenty of experience riding and wrenching on Ducati’s Diavel, and he was impressed. “I was taken aback by the Diavel,” Wells says. “It was fast, and it handled so well despite the huge rear tire and [cruiser-like] geometry. I thought it would be fun to build the first turbo Diavel in the world.”
Reduced cam overlap makes the Diavel’s 11-degree version of the Testastretta engine especially suited for turbocharging, Wells claims. Of course there’s no such thing as an off-the-shelf Diavel turbo kit, so Wells was faced with the challenge of rolling his own. The turbocharger is a standard-issue Garrett dualballbearing GT2860R mounted in a polished TiAL stainless-steel housing, while a TiAL 44mm external wastegate and blow-off valve modulates exhaust-gas pressure. Everything ahead of the throttle bodies and after the exhaust ports is custom-fabricated.
Howerton Racing Products, a well-known Indy Racing League supplier in Indianapolis, hand-fabricated the intake plenum and exhaust system. The 4-liter plenum is roughly half the size of the stock airbox to optimize boost flow.
Making it all play nice with the Diavel’s complex factory electronics package, which includes adjustable ride modes, traction control, and other rider assists that rely on multiple sensors not necessarily ready to deal with added turbo boost, was a considerably bigger challenge. Ducati tuning guru Doug Lofgren massaged the stock Ducati/ Mitsubishi ECU, deactivating the O2 sensor and exhaust control valve input to prevent any warning lights from coming on. The manifold absolute pressure (MAP) sensor also had to be reconfigured to read outside atmospheric pressure instead of actual manifold pressure— before that change was made, turbo boost confused the ECU into thinking altitude had changed dramatically, causing the fuel mixture to lean out dangerously at large throttle openings.
Fuel trim on the stock ECU is set at zero, and air/fuel proportioning is actually managed by a custom Power Commander V built by Dusty Schaller at Dynojet, and informed by a combined temperature/boost sensor housed inside the plenum. Other growing pains included providing adequate fuel supply. The stock fuel pump tapped out once the turbo exceeded 5 psi of boost, so it was replaced with an automotive-style, 40 liter-per-hour fuel pump and an RCC Turbo rising-rate fuel pressure regulator. The fuel injectors are original equipment, modified to deliver higher flow.