Your theory sounds good to me! I am going to put it on the Intercooler. Thanks guys, you all have been a real help.

 

I wouldn't do that if I were you. 12-18 inches away from the throttle body is the standard, I've never even seen a BOV mounted to the intercooler before and I've been around this stuff for a while.

 

I saw a BOV mounted to an intercooler on a rally-prepped Audi 80 a while back. Granted, I don't think this was stock, I think it was done due to space requirements, and this was the ONLY BOV I can think of which was mounted in this fashion.

I've worked on Porsches, Mazda RX-7 turbos, turbo DSMs obviously, Subaru WRXs and STIs, aftermarket turbo Mustangs and turbo Hondas, as well as other Audis, ALL OF WHICH have upper-intercooler pipe mounted blow off valves or compressor bypass valves. There has to be a reason based in physics; I simply don't know it.

 

I had a crazy hypothesis, but it only applied to drag cars. The rally Audi really puts me for a loop.

 

Try this on for size:

First, let's look at this from an air mass perspective. The lower intercooler (pre-intercooler) pipe is usually the same physical size if not slightly smaller than the upper intercooler (post-intercooler) pipe. Both hold similar volumes of air, but the upper intercooler pipe will have more air mass, more air molecules. Above and beyond the piping, the intercooler itself holds the vast majority of the post-turbo, pre-throttle body air mass.

Turbo
Lower piping - least air mass
Intercooler - most air mass
Upper piping - moderate air mass
Throttle body

Air is constantly flowing from the turbo to the throttle body so long as the engine is running. Now with that in mind, imagine a wide open throttle full boost situation.

If the blow off valve were to be mounted on the lower pipe, the virtually all of the air mass in the intercooler and the majority of the air mass in the upper pipe would have to reverse direction to head to an escape point, the blow off valve. Why a majority? Because the engine is still consuming air and as such some of the upper piping air mass will be needed & not vented.

If the blow off valve were to be mounted on the intercooler, its effectiveness would depend on which end-tank it were mounted to. If it were mounted on the hot (lower pipe) side, at least half of the intercooler air mass and most of the upper piping air mass would have to reverse direction to be released. If the blow off valve were mounted on the cold (upper pipe) side, a small portion of the intercooler air mass would have to reverse direction plus the upper piping air mass.

Final option is the blow off valve mounted to the upper piping. Practically none of the air mass in the entire intercooler system would have to reverse direction and could continue to flow normally towards the throttle body as the turbo slows down, only to be vented at the last minute.

 

Well, hold on now...I am by NO means a mechanic. I know very little bout this (hence the reason I am here)...BUT...I have studied fluid and gas dynamics (physics major in college). One thing I do know is this: when you have air flowing at a steady rate down a tube and all of a sudden it encounters a blockage or area of constriction, the air flow does not "reverse". the pressure wave builds up and flows backwards, but not the air itself. A density build up wave. I am not saying that your theory is incorrect regarding the effectiveness (or lack there of), I am just saying the air mass itself will not reverse direction, just the density wave. You will have turbulence though at the initial pressure build up and that WOULD cause a problem for me if it was too long in duration. What is the response time of a BOV? Anyone? That would be the factor in this. If the BOV is quick operating, then A-OK, but if not...then we have a problem. Anyone ever ran tests on the operating speed of the BOV?

 

Use of terminology failed me again. At least the point got across.

As for reaction times, that varies from BOV model to model. Reasonably quick is the average, though, I can tell you that already.

I can't see a rational for going through the hassle of mounting the BOV on the IC. If it was effective and useful, someone would have done it before. Every auto manufacturer we can think of places the BOV/BPV on the upper charge pipe. But hey, if you want to donate your turbo to science we'll be here awaiting the results.

 

My explanation of why the BOV on the intercooler would work is mainly only in extreme applications where it would be used as an anti-lag. For a street application I would most definitely stick with the BOV on the charge pipe close to the throttle.