I have a 91 z28 305 tpi and I'm confused on the types of cams I can use,can it be a flat tappet or does it have to be the roller?whats the difference between them?

 

you can, and should, buy a roller cam.

a flat tappet would work, but you'd lose efficiency, have to buy new lifters, and pushrods. With a new roller, all you'd need is the cam.

The cams would look similar, if sitting next to each other on a table, the difference is in the type of lifters you use, either flat tappets, or rollers.

 

whats the difference between the mech. and hyd. cams?which one would be better if I kept the stock lifters?

 

if you keep stock lifters, those are hydraulic, so you'd need to use a hydraulic roller cam.

If you went mechanical, then you'd get mechanical lifters to go with your new mechanical lifter cam. I don't think thats what YOU want.