Yes! You could possibly, but not likely. Anytime that you change intake or exhaust restriction, you have to compensate for it. listen to your motor, it will tell you when it wants or needs anything.
Running open headers is gonna get the exhaust out of the motor quicker. You might have to richen it up lightly. If your running a low restriction air cleaner also with the headers, probably more so. A stout factory hydraulic cam, that chance increases more.
That absolute best way to tell is looking at your plugs. crank it up, run it some, keeping a eye on your coolant temp., lay a hand on your valve covers, is it hotter? Lay a hand on your radiator hoses, is it hotter?
When you want to absolutely want to know, pull a spark plug. Shoot for a brown or a light brown. Light tan is running lean. A heat gun aimed at your headers will also tell ya what ya need to know.
Careful running lean, you'll blue those pipes quickly, especially running down the road, if they're chromed.