Yes that is normal, I have the same hole on the back of my forge MBC. I think the way it controls how much boost is by doing a controlled leak of air, hence the air hole on the MBC.

If your problem isn't a leak somewhere then I would look at the wastegate as the next possible cause. That is what I was going to replace or mess with next if I was still having a problem.

Let me know how your leak test goes!

 

I had a similar problem, I was getting a hesitation and only getting about 15 psi, with stock tune, no MBC or anything. I pulled the fuel pump out of the assembly and the little rubber grommet from the top had slid down so excess gas was just squirting out the side i guess, but it wasnt getting to the engine at any rate. My replacement grommet cost me $2.00 from STMTUNED.COM

Good luck man!

 

What's up guys! Just before I got to do the boost leak test I decided to just turn on the engine and see if I could just listen for the leak. I mean I was losing the 5 psi needed so I figured it must have been a big leak...sure enough I was able to listen to were the noise was coming from. The coupler that hooks up to the throtle body was intact and had no hole. When I used the tbolt clamp it was in there tight enough its just that it was pushed a lil close from where the pipe starts so it created the coupler to lift up. So what I did was slid the clamp close to the end of the coupler. It sounds confusing, but its all good now. Now all I need is to install the walbro fuel and get tuned