LOTUS INDYCAR ENGINE
Judd opted for a twin turbo configuration, citing bellhousing heat, responsiveness characteristics and inertial differences as reasons for the choice
enough miles on the track yet to know what difference that will make in the car. It’s really a throttle response issue. The idea is a small turbo gives you better response. We just haven’t done enough running on enough cars with enough gear ratios to be sure where we want to be on that. Certainly, I’m well aware that in the 2.65-litre CART days you ran the big turbo on the big ovals and the small turbos pretty much everywhere else.’ Although special attention
was paid to make most components spec, the series left induction piping diameters, lengths and routing open. While its twin-turbo rivals at Chevy opted to take its air from the front of the airbox, Judd elected to feed its turbos from the back of the airbox.
The only major limitation
Judd looked to meet with the piping was the maximum angle of inclination the turbo vendor listed for its units. ‘The shaft can be no more than 20 degrees from horizontal,’ Judd explained. ‘We haven’t seen it vibrate, or just a
for road courses, 20.29psi for short ovals and 18.84psi for speedways. McLaren was chosen as the spec ECU supplier, with its i400 unit allowing the series to have its own set of monitoring sensors and channels to police
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www.racecar-engineering.com • May 2012
three-pin crank and a 60-degree v, the firings would be, say, zero, 60, then it’s 180. Zero, 60 and 240. You’ve got two very close together and two that are apart. You have to consider whether you think this will affect your
very small vibration if it did. If you start talking about greater angles there are other possibilities, but we decided we’re probably better off to respect [the manufacturer’s recommendation].’ Although the series required
the use of the Borg Warner turbocharger, it left the choice of wastegate vendor open to each manufacturer, with Judd opting for units from Parallel Motion, suppliers to Audi’s R18 LMP1 programme, amongst others.
BOOST LEVELS By the end of 2011, IndyCar had finalised its maximum boost levels, announcing 22.47psi
the engines, including assessing instant penalties when over- boost conditions are met. With engine length set at a maximum of 460mm, a maximum bore diameter of 95mm, open stroke and a v-angle limit between 60 and 90 degrees, Judd took all the constraints in mind and opted to go as wide as the Dallara’s engine cover would permit: ‘We made it fairly wide, but not as far as 90 [degrees]. We want to make it as wide as possible for two reasons. One is the c of g. We’ve got space in the centre v as well. And two, to keep the firing angle as far apart as possible. If you have a
“We made it fairly wide, but not as far as 90 [degrees]”
durability in terms of engine parts and the transmission and clutch. The firing pulses overlap quite a bit. It’s like a big three-cylinder engine. We went as wide as we could but we felt constrained a bit by the bodywork and getting in turbo ducts… It’s all got to fit in there. It’s pretty complicated.’ Direct injection is an area of
development Judd was forced to leave off the DC’s initial design brief, due to the time required to develop the system, and its limited potential rewards. ‘It’s designed into the engine and the base end of the cylinder head castings have got bosses. We paid a lot of attention to the ability to use DI in the initial design but we’re not at direct injection yet. Lots of road cars have direct injection and they use it for reasons that are totally different to a racing application. So you’re looking at stratification at low part loads, fuel cuts and all sorts of things it’s very good at, but aren’t related to the full throttle, maximum power stuff that we care about for racing. At the moment, it certainly won’t go
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