B-5 is tough, I barely beat it with an 18.896 time.
First thing first, your speed going in will be slower than coming out. It has to be that way it is a hairpin turn.
The way I went into this was to break very late and very little. So if you happen to have the driver line up, then break about 2/3rds into the red line. Once you are hitting the apex of the turn you should not be breaking at all, you need all the momentum you can get. Once you clear the turn, give the gas a little, to help the RPM get up, complete the turn, then smash on that pedal. The little bit of gas allows the car to that little boost, the high the RPMs the fast your car will be going. I did this in manual, if you haven't, I urge you to try. Having control over the gears makes things A LOT easier, not harder.
So far I have gold on b1-b9. I didnt realize that the game doesnt save the replay, it just saves the time, so alas I cant replay them for you.
Check on Youtube too. Some people have posted some good stuff with very helpful tips. Look at the speed they carry with their cars and the RPMs. A bit more of speed is the difference between gold and silver.
/edit:
Okay I just finished getting Gold on B-License. B-5 and B-7 are the tough ones, everything else is just practice.
Key points I learned from this:
-Keep RPMs high
-Don't turn and brake, brake first, then turn
-Same thing, don't gas and turn, turn then gas
-If you are missing the Gold time by hundredths of a second (.01) the difference might be you just brake too much