Investing in mutual funds for retirement is never too late. And the Zacks Mutual Fund Rank can be an excellent tool for investors looking to invest in the best funds.

How can you tell a good mutual fund from a bad one? It's pretty basic: if the fund is diversified, has low fees, and shows strong performance, it's a keeper. Of course, there's a wide range, but using the Zacks Mutual Fund Rank, we've found three mutual funds that would be great additions to any long-term retirement investors' portfolios.

Let's break down some of the mutual funds with the top Zacks Mutual Fund Rank and the lowest fees.

If you are looking to diversify your portfolio, consider Oppenheimer SteelPath MLP Alpha I (OSPAX Quick QuoteOSPAX - Free Report) . OSPAX is a Sector - Energy mutual fund, which encompasses a wide range of vastly changing and vitally important industries throughout this massive global sector. This fund is a winner, boasting an expense ratio of 1.22%, management fee of 1.1%, and a five-year annualized return track record of 10.5%.

Deutsche Capital Growth S (SCGSX Quick QuoteSCGSX - Free Report) is a stand out amongst its peers. SCGSX is a Large Cap Growth option; these mutual funds purchase stakes in numerous large U.S. companies that are expected to develop and grow at a faster rate than other large-cap stocks. With five-year annualized performance of 16.09%, expense ratio of 0.68% and management fee of 0.46%, this diversified fund is an attractive buy with a strong history of performance.

Janus Henderson Enterprise S (JGRTX Quick QuoteJGRTX - Free Report) . Expense ratio: 1.16%. Management fee: 0.64%. Five year annual return: 11.31%. JGRTX is a Mid Cap Growth mutual fund. These mutual funds choose companies with a stock market valuation between $2 billion and $10 billion.

These examples highlight the fact that there are some astonishingly good mutual funds out there. If your advisor has you in the good ones, bravo! If not, you may need to have a talk.