I know that this is an old post, but I see people talking the most amount of BS.
I have been drag racing a draw thru vw air cooled beetle for more than 20 years.
My engine is a 2 litre and it is making 440 hp. It has been done by lots of people from way back in the 70s. There was guys doing 8 seconds in the 1/4 mile and even today they are still doing those times.
I am running over 28 pounds of boost in my car. And there are guys using much more, and with great success.
You don't need blow through or fuel injection to successfully turbo a car.
I also don't know how any carburettor system can create any vacuum in the engine... That is just stupid. An oil seal is designed to seal oil from getting out of an engine, not for stopping air from getting into the engine. All seals will let air get in, under vacuum.
I would not be pushing much more than 10 psi through a circuit race engine, as you would need better fuel control and water, alcohol injection.
Remember, that a carburettor is designed to be used with out boost going through it, so it is functioning as it was designed to, when using it in a draw thru set up.
Blow thru needs much more modifications to make it work properly. You can buy a very good blow through Holly carburetor now, but you need much more than the carb to make the system work.