I'm trying to add mass to my,inner specs as there isn't much definition there, but my outer specs are fairly developed. I've tried benching with a close grip before without any real results. Any suggestions?
If you go to a gym look for a incline bench press or an incline bench press machine. If you workout at home diamond pushups will yield good results
The muscle fibers in pecs are horizontal. Every chest exercise works the "inner" and "outer" pec, equally as you can't activate one without the other. The way the pec is designed is that the outside is always bigger than the outside and depending on your genetics this may be more or less extreme. It is however possible to stress the "upper", "middle", and "lower" pec . I recommend you do incline press for upper pec. Standard bench press & dumbbell press for middle. Bent over dips for lower pec. Cable crossovers are also great for the chest. Your "inner" pec will develop over time as you bulk up.
Oh and, close grip bench press and diamond pushups put more stress on your triceps not your chest. Wide grip is always the way to go for chest building.
The closer your hands are together, the more you work your triceps, and less pectoral muscles. Best chest exercises I think are decline press and reverse grip bench press
Just because your stressing something more doesn't mean its not working anything else diamond pushups cause a tight close flex on the pecs and cause the inner muscles to be worked. Its like how most back exercises work biceps also. Diamonds can be used for inner muscle definition.
Close grip/diamond pushups just squishes your pecs together and gives the illusion of working the inside. Pecs are unique and like I said before can't be stressed inner/outer, only upper/mid/lower. Feel free to look it up.