How much MPG will I gain from a Mandrel bent exhaust and a cold air intake on my 240sx?

Nissan 240 SX

Nissan 240 SX

I own a 1994 Nissan 240sx. Its the stock standard non-turbo model. I need to get hold of a cold air intake and Mandrel bent exhaust to help with a little power, better sound, and improved miles per gallon.

Tell me please, how many MPG am I likely to get from these accessories? I need to calculate how long it is going to take me to recover my cash outlay from the money I will save from the better fuel consumption figures I will get?

Yes, I know it is a tall order.