I'm thinking about putting a cam in my truck but want to leave the stock setup what size can I put in with out doing the valves

 

Most aftermarket cam require a new set of valvesprings matched to the cam's lift and duration. There are a few drop-in cams that can use stock valvesprings but they are relatively small, like some of the Cam Motion cams. Even then they recommend a set of stock-rate springs. Springs wear out and can be considered sacrificial parts like brake pads or something.

Similar deal for pushrod length. Some smaller cams can reuse stock pushrods, but it's always a good idea to check pushrod length when changing cams. Upgrading pushrods is cheap insurance. Higher lift increases spring pressure on the pushrods, so they can start to deflect even with mild cams and moderate RPMs.

Roller Lifters can be re-used, but if they have more than 150K miles on them it's a crapshoot if the rollers are shot or not. High mile LS engines like to eat lifters and cam lobes.

Stock LS1 style chains are weak, you'll get chain stretch with a hot cam and a stock single row chain. A single roller LS2 style chain is good for most street applications and will fit under stock oil pump/front cover without mods.

So yeah, you can get off cheap with just a cam. Just know that failing to replace springs/pushrods/lifters/timing chain as well, has often caused engine malfunction or damage after a cam swap.

 

do valve springs and pushrods

 

If you plan on running the stock transmission/stall converter the largest cam I would go with would be 212/218, 210/218, 216/220 duration cams.

 

Need more info on the build. Your asking the blind to lead the blind by not giving us enough info.

 

Basically it sounds like he wants a cam but doesn't want to buy any parts needed for a cam swap. So you should just leave the truck alone or pull 2 plug wires and injector pig tails so it'll cut up and drive different

 

http://www.hotrod.com/how-to/engine/1307-ls-cam-test-comparison/
Scroll down to the bottom crane camd offers one no spring change required

 

Keep in mind fellas we know absolutely nothing about this truck. Is it NNBS? Nbs? Nnnbs? We know he wants a cam in a 5.3 truck with no changes.

 

A cam that requires no tuning, valve springs, or pushrods is not worth the time to swap it. Might possibly gain 5-8hp if that.

 

Impossible to put a cam in without doing anything, you have to at least get the timing cover off

We need a LOT more info, but as a general rule a cam is way down on the mod list, start with CAI/exhaust/headers/stall/gears... Then start toying with the idea of valvetrain and engine mods. If you want a lope at idle just tune the idle rpms down until it almost stalls and take some out of the spark table