How many crunches should I do a day for four months to develop your standard lean six pack abs?

First question is... do you have a lean body to begin with? You can do 1000 crunches a day, but if you don't have anything less than 8 - 10% body fat... chances are, they won't show.

I usually do about 500 crunches a day, 250 in the morning, 250 in the evening, in sets of 50s.

Decline situps. I used to do 40 of them 3 times. Crunches don't have much movement to them and that's why people do so many of them and that's why few people have six packs because everyone thinks they'll do the trick--that and no one stays consistent with them. LIsten to Sneezefunny. He/she knows what their talking about. You need to be lean to begin with, and don't expect situps or crunches to burn away the fat, you need to burn a mess of energy to do that.

I'm actually already lean according to everyone who has seen me with my shirt off I just wanted a six pack.

Do a mix of work... situps only engage some muscles at your waist and can cause problems when not done properly.

I do a mix of situps, both on an incline bench and flat (but I do them as taught in pilates, which engages the muscle before you lift and controls your breathing)... with some straight on and some twists, crunches, leg lifts (hanging from a bar), and twists. I also work a heavy bag once or twice a week and do tae bo 3-4 times a week, and this can get good twisting motion at your core.

I hate to tell you but you will need to do more than just that.. Running sit ups cruches and all the normal stuff is a need for good six pack abbs