The term ‘blockers’ was used extensively on Sunday at a steamy Thermal Club Grand Prix, where ambient temperatures hovering around 90 degrees and a rare race with no caution periods caused problems for some of IndyCar’s bespoke energy recovery systems (ERS).
In fact, blockers did affect the event’s outcome as Chip Ganassi Racing’s Alex Palou was able to use the extra horsepower offered by his ERS unit from start to finish.
“We never had to pull back with the hybrid; Alex had it to use the entire race,” Palou’s race strategist Barry Wanser told RACER. “We knew it was going to be one of the hottest races of the year so we worked a lot with blockers to figure out the best plan. We ended up running more open (with blockers) than we probably ever have since the hybrids came in.
“It ended up being close (on maximum temperatures), but Chip always tells us to do the simple things right. So we opened things up, and Alex never had an issue and could use the hybrid the whole time.”
Polesitter Pato O’Ward was forced to avoid deploying full hybrid power during half of the 65-lap race due to an overheating ERS.
“Yeah, for 50 percent of the race I couldn’t use the thing. Just overheats,” O’Ward said. “Obviously here it’s probably one of the most helpful areas where the hybrid is of good use, because of those very stop-and-go corners and long straightaways.”
Worth 0.3s per lap, having ERS power available at all times would not have allowed O’Ward to keep Palou behind him due to differing tire strategies that benefited the Ganassi driver. But being able to subtract 0.3s from each lap wouldn’t have hurt.
“In race trim, if you’re asking me if I would have won that race if I didn’t have those issues, the answer is still no,” O’Ward said. Teammate Christian Lundgaard also acknowledged having ERS overheating issues that limited his use of the system.
According to Wanser, Palou’s No. 10 Honda team knew of the ERS limitations being experienced by O’Ward and Lundgaard. Both avoided deploying its power in order to let the units cool slightly and come back into play, before that usage pushed the temperatures over the limit and a new round of avoidance and cooling was required.
“All the teams monitor each other’s communications, and we heard they (Arrow McLaren) were experiencing high temperature problems,” Wanser said. “And we shared that with Alex, and that just make him sink his teeth into tracking them down even more.”
So what are blockers, which also go by the name of ‘shutters,’ and what purposes do they serve?
Chevrolet and Honda both provide their teams with guidelines for optimal water and oil temperatures to maintain when the cars are on track. And whether it’s a cool day at Barber Motorsports Park or a scorcher at Thermal, teams install blockers on the backside of the large radiators in the sidepods to restrict airflow through the radiators to bring engine temperatures up, or remove blockers to increase airflow and prevent overheating when it’s exceptionally hot. With the addition of IndyCar’s new ERS units last summer, a small ERS cooling radiator is now also part of the package and sits in the right sidepod.
If there’s a swing in temperatures from morning to afternoon, teams will make adjustments to how many blockers are used. Blocker changes happen between almost every session to ensure engines run in the optimal temperature range that delivers peak performance, and with the ERS radiator in mind, blocker changes also have an impact on ERS cooling.
But there’s also a secondary approach to using blockers, and that’s as aerodynamic tuning devices that affect downforce.
On hot days when engine cooling is marginal, running with a limited amount of blockers — or no blockers at all — will keep the motors in an optimal performance range and flow plenty of air through the ERS radiator. But that high volume of air being allowed into the sidepod increases aerodynamic drag and slightly reduces downforce.
By pushing close to the edge of overheating through installing more blockers, the drag penalty is reduced and more air is used to make downforce, which can be used to improve lap times.
Deciding whether to use more blocking of airflow through the radiators to gain a slight downforce advantage while running the risk of the motor and ERS unit boiling over, or opening up the airflow, keeping the engine and ERS below their temperature thresholds, and forfeiting a modest amount of downforce, was where the Ganassi and McLaren teams diverged on Sunday.
Had a caution or two emerged and given the field a chance to run at reduced speeds and cool their cars, it’s possible that O’Ward, who led 51 laps and placed second, and Lundgaard who started second and placed third, could have joined Palou in deploying ERS power for all 65 laps.
“It was nothing intentional on our side,” said Arrow McLaren technical director and O’Ward’s race strategist Nick Snyder. “In hindsight, we probably should have adjusted our blocker configuration a little bit. Certainly didn’t go into the race expecting to have any issues, but this is the hottest, longest we’ve ever run, and IndyCar bumped up the energy limits for this event, which was great. We were totally fine in qualifying, but just the long run in the race with no cautions, we had a little heat soak there and just ended up on the high side of temps.
“So more, from a conservation preservation standpoint, we could probably go back and make a couple of adjustments and give ourselves some more usability. We just missed it a little bit on our side, in terms of what that (blocker) configuration looked like.”