Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of American Axle (NYSE: AXL) leapt 12% in early Friday trading before pulling back to net "only" an 8% gain by trading-day's end.

So what: Per-share adjusted profits of $0.69 at the -- you guessed it -- American car-axles manufacturer beat Street expectations by more than 50%. Net profits were a similarly strong $0.65 per share. Best of all, management says there are more gains in store for later this year. Full-year sales could reach as high as $2.6 billion, and AA is looking to make perhaps a 15% EBITDA margin on those sales.

Now what: That works out to perhaps $390 million in EBITDA for the year, or roughly twice last year's number. If net income likewise doubles, we could be looking at perhaps $230 million in earnings for fiscal 2011, enough to give the company a 3.8 current-year P/E ratio.

Wall Street's not predicting anything like that, however. Right now, current-year estimates call for AA to earn perhaps $1.80 per share. That still works out to only a 6.4 P/E ratio on this projected 18% grower. At the risk of understatement, that's not a lot to pay for this muffler (and yes, I know they don't make mufflers.) Seems to me that while American Axle ran far Friday, it could still have more room to run.

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This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.