I'm not sure what phunkdokta meant by that, but I hope this doesn't degenerate into a name calling match.

As for a blow off valve, you hit the nail on the head with your description of the blow through system. Please don't use a blow off valve on a draw through though! It will vent the pressure yes, but that pressurized air will also contain fuel! Imagine the sound then, "ssssssrrrrrreeeeeet, piiiiiiiisssssssshhh, KABOOM!"

I would never of guessed that you would have been a Tool#@$%

Im planning on wacking a turbo on my a12 120y as i am a toolmaker i can do pretty much everything my self BUT

there is one thing i wont to clarify from arguments ive read on this page about the dreadid Blow off Valve's on carby turbos
the lag difference with or without is a whole different argument but i do know this

on a draw throught turbo setup the BOV is a wank value item (unless your fighting lag)
on a blow through turbo setup a BOV is a good idea for a smooth running system.
cos when you lift your foot off the go go pedal (ie changing gears) you create vacuum in the manifold which draws petrol through the idal jet!! all good but if you have boost on the other side of the throttle (cos the turbo will still be spinning) you have a great pressure which pushes more fuel out than its spose to have causing a sudden rich condition which deteriorates the engine response.

but with a BOV as soon as you lift off the throttle the BOV lets off the presure equalising the presure on both sides of the throttle!!!
and you have a smother and more ecinomical carby turbo setup!

And if you dont like the kool sound then route the air into the filter box which will quiten it down!!
not that i'd wont to do that there is nothing kooler that a stock looking 120y stock rims comming down the road with the sound of the tubo spoolling and then pshhhh of the BOV bound to catch a few people off gaurd!!

(sorry about the spelling)