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Cool. Let us know how the MS install goes. Lee's the MS man so it should be all good. 
Well thats a nice big giant turbo you have. Corky has the simplest blurb about this issue in chapter 12 - boost controls. He says "Boost pressure can be vented after work is done to create it. Effective, but a bad idea." and he goes on to say that they're best used as overboost safety devices. Its a very opinionated section and doesn't really explain too much in the "why" department.
The interesting side effect of venting the compressor for boost control is that you can't read a compressor map the same way you would if you were using a wastegate. As a matter of fact, it kind of blows using a compressor map out of the water. I think the best way to explain "why" it may be less efficient to vent is to go ahead and take a look at whats happening on the compressor map. Shame I can't find a compressor map on that thing. I'll use a 20g map cause its plenty big. Not as big as the 61 but hopefully you'll get the idea at least. For these examples I'll use 7000 rpm, 100% VE, and a max boost of 12 psig to keep things simple.
With a wastegate control, the engine demand line for any particular RPM follows a linear upward course and ends up as a finite point at maximum boost. The efficiency points are finite because the wastegate keeps the compressor speed in check and only allows it to spin as fast as needed for the desired boost level. In this example, efficiencies are plotted from 3 psig to 12 psig, where we ultimately end up at 77% efficiency.
With an intake vent, engine demand and boost level are used as boundries for an efficiency section. In this case, efficiency is not finite because the only thing we really know is the LEAST amount of airflow that is required to sustain the desired boost level. In this example, we're looking at what the possible efficiencies are at 12 psig only.
Thats the reason I said that venting kind of blows using compressor maps out of the water. They become unusefull basically. But they do show why it's not really a good idea to vent the intake for boost control. The efficiency section will always go off the map, and you already know if you get off that map the efficiencies just plummet. There's no telling how much work the compressor is going to do. You can measure the efficiency by looking at the intake charge temps, but what you'll find is that the efficiency is variable for every scenario. Some of the variables are how long you've been at max boost, and how much extra energy the exhaust can generate at the turbine while at max boost. I'll also say that all of this hoo-ha is theoretical and I may have the section drawn incorrectly. I drew the left boundry as a continuation of the engine demand at 7000 RPM. Maybe a more realistic view would be that the left boundry follows engine demand initially, then starts to head east until it plateaus at a pressure level that can be sustained by the exhaust energy generated at max boost. <EDIT>Thinking about it a bit more, maybe an even more realistic view would be that the left boundry goes straight up at the specific CFM for the engine demand. </EDIT> Thats not so important...the important point is that there is no precting how efficient the compressor will be.
With that big ol snail you got, it may never go off-map. Hell, it may even be more efficient in certain scenarios. Who knows. But in general, the fact that the efficiency is truely variable mixed with the possibility that the compressor even has a chance of going off-map and getting so very inefficient just makes it a bad idea. Corky may not have explained it too well but I do agree with him on that opinion.
95 Eclipse RS : 5 speed
15.7 @ 87.9mph
Jeep TB writeup - http://www.dimensia.com:81/jimbo/JeepTBfor2gnt.html
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