Crunches are funny things. The word makes me think of Cheetos. Unsure why.
The thing is, you can blow through a set of 50 crunches without feeling even 1 of them. Well, you'd feel the first one. After the first one, you can kind of just coast to the end of a set without really getting much benefit. This is because your abs are made to bounce. Not really "bounce." Actually, your abs are MADE to transfer energy. It's what they do. Think about it. When you throw a ball/punch/etc, what are the primary movers? Yep, legs, hips then finally the arm. What muscle groups bridge the effort between the lower and upper body? It's the abs.
In nature, your abdominals primarily function by making small stabilizing movements. As long as you keep the actual movements of the torso predominantly small - you are playing to their strength.
When you step out of the realm of small movements, as with abdominal exercises (when done correctly), you ask more of them than they are naturally used to. This taxes your abdominals considerably more!
My point is, you should make BIG movements with those crunches today. You aren't here to blow through reps as if blowing through a bag of Cheetos. You are here to tax those abs. Light them on fire. The only way to do this is to work them throughout their entire range of motion. Crunch all the way to the top of the movement and stretch out all the way at the bottom.
I realize these pics are reposts, but I wondered if you might appreciate them more after having done a few of these yourself a couple of times over the last week, or so?