Usually in a case like this, the best way to get a raise is to ask that you be reclassifed to a new position and title. You are a manager not a dev and you should have the payscale that managers have. This is a promotion and you need to have that acknowledged and paid for. 

The last time I did this type of thing, I went to my boss and said now that I am doing the tasks of  a _______, I would like to offically be given the postion. It is often easier to justify a larger raise when you change job titles. HR generally has a payscale for each job that they try to stay within. The manager ones are generally (but not always) higher, so shoot for getting a promotion not a payraise.