Hey guys I have a 2003 ltz400 it has pro flow kit and full lrd exhaust as far as engine work goes. I was wondering what a stock bore high compression piston no porting, just piston, prob no cams either cuz it's my g/f's bike but I like to ride it ocassionally. Anyways what could I expect from that mod is it even worth it? thx guys

It would be a nice little gain nothing to write home about, but worth it for the cost. Try picking up a used hotcam intake cam or hit up woodward for a new one and make it worth it. Otherwise a nicer mod on the z besides the piston is an fcr from a yfz, makes for a snappier little 400cc.

Cool thx I have another q's then as far as the cam is concerned the bike is pretty much used for the dunes very little trail time so do I just do the intake cam or both intake and exhaust and is there a good place to look for a used cam and is it a bad idea to buy a used cam?

I would install only the intake cam unless you're running a bigger motor, higher compression, etc. Sometimes the addition of the exhaust cam sacrifices too much bottem end, that feeling is amplified when you add drag or strain on the motor like with dune riding. If you were to go higher on the compression, maybe some porting, better intake and carb; then I would run both cams because the loss of low end grunt wouldnt be as noticable compared to what you gain throughout the powerband. I would use a used cam if the lobes were in good condition, if the its well taken care of and low hours. Definitely hit up z400central for parts, and if you decided that you have to have an aftermarket exhaust cam I have a brand new exhaust cam (hotcams) that I'd let go.

i might be able to help you out here... my buddy just bought a 435 venom piston to put in his bike... he's got a 13.1 piston now and if you put the drz e base gasket on it. it will make it 13 1/2.1. i don't really know what cams he's goin to put in, but he's got the yoshi cams right now... he hasn't made up his mind whether to sell them or what. i know he's not goin to put the stuff in in the next week or so, but it will be soon. i guarentee the piston to be good... he maintains the bike to a tee... send me a pm if your interested in what he's got...

I dissagree completely.
This has been debated countless times over a Z400central. For a dune machine shooting hills, etc, the engine needs to breath. The HC (In & Ex) aren't huge duration or lift cams and work fine with the stock carb. Your not going to loose any significant bottom end. You have a full exhaust, so help it out with the exhaust cam too. You'll be kicking yourself after if you don't.
I'd also consider a +1000 rpm CDI, but you'll need to upgrade the valve springs to the DRZ style. This is a cheap mod combo and should make for a nice well rounded dune quad for the g/f.
Add an FCR down the road to further compliment the cams and (hears that phrase again) let the engine breath.