How do you blow a big load during sex?

- make sure you are well hydrated (ie drink water regularly).

- stay healthy (exercise, don't smoke, etc)

- don't blow your load for a couple of weeks, but make sure you get yourself partly worked up by looking at porn, or looking at strippers.

- then, on the day when you do want to bust your nut, take your time and try to last as long as possible before having your orgasm. The more worked up you get the bigger and more powerful your load will be.

Answer taken from Jizzblog.