Group 1 Automotive (GPI) could be a solid addition to your portfolio given a notable revision in the company's earnings estimates. While the stock has been gaining lately, the trend might continue since its earnings outlook is still improving.Analysts' growing optimism on the earnings prospects of this auto dealer is driving estimates higher, which should get reflected in its stock price. After all, empirical research shows a strong correlation between trends in earnings estimate revisions and near-term stock price movements. This insight is at the core of our stock rating tool -- the Zacks Rank.The five-grade Zacks Rank system, which ranges from a Zacks Rank #1 (Strong Buy) to a Zacks Rank #5 (Strong Sell), has an impressive externally-audited track record of outperformance, with Zacks #1 Ranked stocks generating an average annual return of +25% since 2008.For Group 1 Automotive, there has been strong agreement among the covering analysts in raising earnings estimates, which has helped push consensus estimates considerably higher for the next quarter and full year.The chart below shows the evolution of forward 12-month Zacks Consensus EPS estimate:12 Month EPSCurrent-Quarter Estimate RevisionsFor the current quarter, the company is expected to earn $6.62 per share, which is a change of +75.6% from the year-ago reported number.Over the last 30 days, one estimate has moved higher for Group 1 Automotive compared to no negative revisions. As a result, the Zacks Consensus Estimate has increased 15.42%.Current-Year Estimate RevisionsThe company is expected to earn $22.91 per share for the full year, which represents a change of +26.85% from the prior-year number.There has been an encouraging trend in estimate revisions for the current year as well. Over the past month, one estimate has moved up for Group 1 Automotive versus no negative revisions. This has pushed the consensus estimate 8.02% higher.Favorable Zacks RankThanks to promising estimate revisions, Group 1 Automotive currently carries a Zacks Rank #1 (Strong Buy). The Zacks Rank is a tried-and-tested rating tool that helps investors effectively harness the power of earnings estimate revisions and make the right investment decision. You can see the complete list of today's Zacks #1 Rank (Strong Buy) stocks here.Our research shows that stocks with Zacks Rank #1 (Strong Buy) and 2 (Buy) significantly outperform the S&P 500.Bottom LineGroup 1 Automotive shares have added 12.5% over the past four weeks, suggesting that investors are betting on its impressive estimate revisions. So, you may consider adding it to your portfolio right away to benefit from its earnings growth prospects. Bitcoin, Like the Internet Itself, Could Change Everything Blockchain and cryptocurrency has sparked one of the most exciting discussion topics of a generation. Some call it the “Internet of Money” and predict it could change the way money works forever. If true, it could do to banks what Netflix did to Blockbuster and Amazon did to Sears. Experts agree we’re still in the early stages of this technology, and as it grows, it will create several investing opportunities. Zacks’ has just revealed 3 companies that can help investors capitalize on the explosive profit potential of Bitcoin and the other cryptocurrencies with significantly less volatility than buying them directly. See 3 crypto-related stocks now >>Want the latest recommendations from Zacks Investment Research? Today, you can download 7 Best Stocks for the Next 30 Days. Click to get this free report Group 1 Automotive, Inc. (GPI): Free Stock Analysis Report To read this article on Zacks.com click here.