Cooler temperatures, increased grip and faster speeds put heavier loads on engines this past weekend at Chicagoland Speedway, and before the NASCAR Sprint Cup Series race had been completed, more than half a dozen drivers in the 43-car field had been sidelined due to engine-related issues.
Most notable among those hit were Joey Logano and Dale Earnhardt Jr., two of the 13 drivers that make up this year's Chase for the NASCAR Sprint Cup field.
In a race that was interrupted for more than five hours by rain, there was growing concern up and down pit road as teams attempted to anticipate how the delay and unexpected weather conditions would impact engine durability.
The expectation had been for a slower pace under much different conditions. Faster lap times over an extended period put much more stress on the parts and pieces under the hood -- parts and pieces that had already gone through an unforeseen heating and cooling cycle brought on by the red-flag period.
"You aren't kidding," said Alan Gustafson, crew chief for the No. 24 Hendrick Motorsports Chevrolet of Jeff Gordon. "When we were out there running 29.30s (lap times in seconds) leading the race, I'm like, 'Holy moly, that's crazy fast.'"
"When you practice at 120-degree track temperature and it's sunny, and you're out there running 30-ohs your fast lap and after five to 10 laps you're running 31s, you didn't think you were going to see any 29.30s," he said. "It's amazing fast."
Gustafson and Gordon were among the more fortunate. Each manufacturer had at least one prominent failure.
Kevin Harvick, who finished third, said the pace of the race definitely picked up after the rain delay, and on more than one occasion he hit on the rev limiter.
"I hadn't touched it all weekend," the Richard Childress Racing driver said.
Logano, who set a track record in winning the pole two days earlier, then led the first 32 laps, said he was "having to lift early in Turn 1 because I was up against the (rev limiter) chip."
Although some drivers are tougher on engines because of their driving style, engines aren't tailor-made to individual competitors, according to Doug Yates, head of Roush Yates Engines.
Yates said his group builds engines based on the "worst-case scenario" with the hardest driver.
"If it passes that guy's style, then it will work for everybody else," he said. "The base engine is based around that hardest guy who carries the most speed into the corner and has the most on-throttle time."
Whether or not steps could have been taken before the resumption of the race to lessen the chances of breaking an engine, winning crew chief Jason Ratcliff said a gear change, which would affect the RPM range, "would have made the most difference."
"I think the RPMs in the end was the culprit," he said.
"It's extremely hard (on an engine) when you get hot ? you're turning 9,500-plus RPMs. You go through a rain delay ? everything cools off. You get a lot of heating and shrinking. If you don't heat the oil back up before you start them, it can be tough on them. You try to do the best you can, considering the circumstances.
"And ? there's so much grip ? even before the rain delay, even before it cooled off another five or six degrees, these guys were out there running crazy lap times, a lot of sustained RPMs at the end of the straightaway."
Push it hard enough, Ratcliff said, and "something's going to give."
FULL SERIES COVERAGE