With pistons not homologated, these and the attendant compression ratio are crucial for the tuning potential of the engine. After that, it’s down to the ECU
and minimise friction, obviously. And to make some decisions about compression ratio, which, of course, will affect efficiency. This really takes on board stroke, the angle. You’ve got to think – it’s a V6, it’s balanced pretty well, so you need to sort out the firing process and what configuration crank you’re going to use. The rev limit means probably if it was a 2.2-litre V6 for F1 that, say, revs at 18,000, you’d almost certainly have bought a shorter stroke and a bigger valve than you’d do for this application.’
CONVENTIONAL TUNING Once built, EDL had a finite window to work within, as the series closed homologation 30 days prior to the opening round on March 25 2012, leaving Judd to stick to more conventional tuning areas. ‘You do all the usual things
like cam timing, lift, fuel injection, injector positions, fuel pressure, injector type, compression ratio, make sure the crank’s not stirring up oil in the sump etc,’ he explained. ‘So you’re basically working with this stuff all the
time, in conjunction with trying to sort it out, to maintain and work on the durability and production manufacture issues as well. It’s all inter-related. But in terms of power, it is breathing, cam timing, friction, compression ratio and mixture preparation.’ With the DC homologated, the
usage profiles with different boost specs for small ovals and road courses. And the race will take place in different weather conditions – some hot, some cold – so to get a handle on durability in race conditions is something, I think, we won’t know about until we’re in the race. For us, I think
“We did the modelling and
design with SolidWorks, and all the programmes that go with that”
number of performance items to exploit has been greatly reduced, but Judd still has a few items to play with. ‘Homologation leaves the compression ratio pretty much free because the pistons are not homologated. The rules were drawn up in connection with engine people and I’d say there’s nobody that wants to be tied down to a piston design right now because we don’t know how durability is going to turn out. It’s quite hard to know the
the biggest single component affected by the usage profile is the piston. Most of the rest of the in-season tuning will come from the ECU.’
ONE GOOD, TWO BETTER? Judd opted for two turbos, rather than one, citing the difference in physical placement – either the traditional inside the bellhousing for single, or parallel to the exhaust ports for twin – as one of the considerations. But the
series balanced the sizing of the Borg Warner turbine housings to provide equal airflow between single and twin turbos, and responsiveness characteristics and inertial differences also factored into the Lotus’ final spec. ‘It’s a good old trade off,’ he said. ‘The HPD [Honda] has a nice, simple [single turbocharger] layout. I don’t know if there’s any weight difference or not. We thought at the end of the day the twin would be better and we were pretty concerned about the heat in the bellhousing in the single. We saw all that years ago with the CART stuff.’ IndyCar will permit the changing of housing sizes to optimise performance for different circuits, but once the single Borg Warner EFR9180 (with an A/R of 1.05 or 1.45) or twin turbo EFR6758 (with A/R of 0.64 or 0.85) layout has been chosen by a manufacturer, it cannot switch between single or twin turbos.
‘The small turbine has the higher back pressure and there’s a power penalty for that,’ continued Judd. ‘We don’t have
May 2012 •
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