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Why an independent rear suspension for GM's new, full-sized SUVs wasn't easy

A Motor Trend report last month laid out how Cadillac's 4.2-lier twin-turbo Blackwing V8 could be an orphan due to cost concerns in the GM empire. Last-minute chassis changes to Cadillac's new sedans and XT6 crossover led to engine bays that couldn't fit the Blackwing. On the SUV side, according to the report, the new independent rear suspension for big people haulers cost so much to implement that GM ruled out reworking the Escalade to accept the Blackwing. At least one commenter rightly asked how could a suspension swallow that much money. A new piece in Motor Trend has the answer. The excellent Alissa Priddle spoke to Tim Herrick, GM's executive chief engineer for full-size trucks, about why the clean-sheet IRS cost "multimillions of dollars."  First, GM would need to build a new body shop at the Arlington, Texas plant that assembles the automaker's big SUVs to stamp the numerous wholly new parts and panels accommodating an IRS. Then GM would need to design and pay for a new assembly process. On top of those up-front costs, there was the incremental cost of the four-link IRS components being more expensive than those in the trucks' former leaf-sprung solid axles. Herrick endured so many rejections for so long that he remembers the date and time when he got approval for the new unit. He said it came down to a meeting where he told a higher-up, "I'll make you a deal: If we get to the reveal, or if we launch this and you think this was a dumb idea, I'll hand you my badge and let you walk me out." Head to Motor Trend to read the full story. Based on Herrick being on stage to help present the new SUVs to the press, and on our First Ride in the new Chevrolet Tahoe and Suburban at GM's Milford Proving Grounds, it appears this will have a happy ending for all involved. Furthermore, since Herrick worked on the T1 platform that supports the big SUVs as well as the light- and heavy-duty pickups, he understood the demands on the commercial side, too. That could be why when Roadshow asked Tim Asoklis, chief engineer of the Tahoe and Suburban, if the new IRS could endure life in the Chevrolet Silverado and GMC Sierra, Asoklis answered, "Oh, absolutely." Related Video:    

'Killing a Duramax' Gale Banks YouTube series methodically tunes a diesel to death

Learning or perfecting a skill by watching YouTube videos is known as attending YouTube University. GM Authority picked up on one of the video site's more fascinating courses, hosted by Gale Banks; in a fair world, he should be referred to as Professor Banks when it comes to diesel engines and truck tuning. A few months after GM introduced the updated L5P 6.6-liter Duramax diesel V8 in the 2020 Chevrolet Silverado HD and GMC Sierra HD that ships with 454 horsepower and 910 pound-feet of torque, Banks decided he wanted to methodically tune the engine to death. The purpose of the resulting series, called "Killing a Duramax," is to push more power out of the engine in order to discover which parts break and when — or, as Banks puts it, force-feed the Duramax "until the crank hits the street and the heads hit the hood." With that knowledge, Banks can figure out all the weak points on his way to building what he calls a "Superturbo," that being a supercharged, twin-turbo race engine with more than 1,000 hp. What makes the series fascinating is Banks' knowledge, paired with the company's comprehensive iDash engine monitoring system that keeps tabs on a glut of parameters every step of the way. So for instance, you get Banks explaining the differences between inches of mercury and barometric pressure, how those are different from the water content of the air measured in grains, then showing those readouts on the iDash, then explaining in detail how they affect the air density in the Duramax system. The stock Borg-Warner variable turbo gets a lot of airtime — Banks accuses it of being "out to lunch" because he feels it's the weakest link on the engine. That turns into a turbo teardown and a deep explanation of performance pitfalls, such as when air pressure on the turbine begins to diverge from the boost pressure coming from the compressor. Banks says he can keep close tabs on where power's coming from, because the iDash monitors the horsepower contribution provided by the ambient air, the turbo, and the intercooler separately. The major changes so far are a stouter Precision 7675 turbo and TurboSmart wastegate (episode 5), a twin intake (episode 6), a custom liquid-cooled intercooler from a marine engine, a new GM oil cooler and synthetic oil (episode 10), and new injectors (episode 11).

GM will stop reporting monthly U.S. vehicle sales

DETROIT — General Motors said on Tuesday it will stop reporting monthly U.S. vehicle sales, saying the 30-day snapshot does not accurately reflect the market, and will instead issue quarterly sales. GM will also no longer report monthly sales in China, its largest market, and Brazil. GM will provide monthly data to the U.S. Federal Reserve, industry associations and government agencies across the globe, but that data is not made public. Analysts and investors rely on monthly U.S. vehicle sales not just to track the performance of individual automakers, but as a barometer of the health of the world's second-largest auto market and as an indicator of consumer confidence in the U.S. economy overall. GM and its Detroit rivals Ford and Fiat Chrysler have relied heavily on sales of high-margin pickup truck and SUV sales to boost profits. GM's total U.S. sales, its second-largest market, are down 3.2 percent for the first two months of 2018, reflecting a 6.8 percent drop in retail sales to individual customers, the company reported last month. GM executives have expressed frustration that comparisons of monthly U.S. sales results among rival automakers are distorted by short-term discount programs, and by differences in strategy for selling vehicles in bulk to rental car fleets. "Thirty days is not enough time to separate real sales trends from short-term fluctuations in a very dynamic, highly competitive market," Kurt McNeil, U.S. vice president for sales operations said in a statement. GM's actions could prompt other automakers to also switch to quarterly U.S. sales reports. Major automakers will report March U.S. new vehicle sales on Tuesday. Until the early 1990s, most U.S. automakers released sales results every 10 days. The former Chrysler Corp. stopped reporting sales on a 10-day basis in 1990, and rivals followed suit over the next three years. GM executives are betting that investors will quickly adapt to receiving U.S. sales data every three months, as investors in other retail sectors already have. Retailers such as Walmart report sales on a quarterly basis. Reporting by Joe WhiteRelated Video: Image Credit: Reuters Earnings/Financials Green Buick Cadillac Chevrolet GM GMC US