Westport Innovations (NASDAQ:WPRT) and Clean Energy Fuels (NASDAQ:CLNE) are often talked about together. And while Westport Innovations is certainly relying on Clean Energy Fuels' "America's Natural Gas Highway" to make the shift from diesel to natural gas a viable choice for truckers, its diverse global opportunity means that it's less reliant on Clean Energy than Clean Energy is on Westport. 

And with Westport's earnings just having come out last week, there are a few hints that can help us see how things are playing out for Clean Energy, a little bit before its earnings come out this week. Let's take a look.

It actually goes back to Cummins
Cummins 
(NYSE:CMI) reported on October 28, and the overall reception wasn't positive, as the company cut its outlook. And while investors in Cummins should keep an eye on this, it's critical for those of us who are looking to Cummins' results for data about the natural gas truck market to dig in a little deeper, because its natural gas engine business -- specifically the Cummins-Westport (CWI) joint venture -- is actually performing well. CEO Thomas Linebarger, from the earnings call: 

"So we rolled out the full line in August with the higher ratings and in fact the acceptance has been good where again we're now engineered in with all the OEs in North America, in fact our sales are running a bit higher than our internal projections."

It's important to remember that Cummins is a very diversified engine maker, and while important, the North American heavy-duty truck market is just one part of its business. And while the company's outlook for the near term isn't great, this one segment is performing well. 

Westport confirms, adds color on Volvo
CWI's results for the quarter were strong, with total units sold up 52%, and revenue up an even stronger 70%. And this number -- revenue growing faster than units -- points squarely at the new 400hp engine, which is both the most expensive in the joint venture and the key engine for truckers, as being the source of growth. Additionally, we learned that the new engine that Westport is working with Volvo on won't be available until "late 2014," Per CEO David Demers on the Westport earnings call. 

But for Westport it is looking like China is a more significant opportunity. Its joint venture with Weichai Power is both larger ($373 million rev. YTD versus $200 million) and growing faster (126% YTD versus 29%.) And while margins are much slimmer at the Chinese JV, the scale alone could turn this venture into the bigger profit opportunity. Hence Westport being less reliant on Clean Energy's ANGH for success.

The other Westport announcement: How 900 becomes 37 million
Maybe the most positive news from Westport on earnings day, at least for Clean Energy investors, was the announcement that Universal LNG ordered 900 of the company's iCE PACK LNG tanks, which are pretty much guaranteed to feed CWI 12 liter engines, which means heavy-duty trucks. And with Clean Energy having by far the largest infrastructure, there's a better-than-average chance that it will get the fueling business. So how much of an impact on its business is 900 trucks?

Assuming that each truck uses an average of 15,000 gallons per year, and the retail price of the fuel is $2.80 per gallon (a 30% discount versus $4 diesel,) that's about $37 million per year in fuel sales, or roughly 10% of Clean Energy Fuels' total revenue for the past 12 months. 

Final thoughts
Westport's biggest opportunity may not be in North America in the long run, but the earnings release and iCE PACK announcement both bode well for Clean Energy Fuels, whose business is largely tied to North America for the foreseeable future. Most importantly? The information we can glean from other company's earning announcements is nice, but it's not enough to act on. Without having the full context of how these activities at its peers translate to results for Clean Energy, they can lead investors down false trails. Use them to inform your opinion, but not to make a decision. Because until we see exactly how these things really affect Clean Energy, it's just noise.

Jason Hall owns shares of Westport Innovations and Clean Energy Fuels. The Motley Fool recommends Clean Energy Fuels, Cummins, and Westport Innovations. The Motley Fool owns shares of Cummins and Westport Innovations. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.