I am interested in finding out why InlinePro put the BOV closer to the turbo and not closer to the TB. In most applications I've seen (mostly for Integra's) the BOV is closer to the TB past the intercooler. I thought this would be the best design since once the TB closes the excess pressure blows off ASAP. InlinePro's design seems like you would have more charged air pushing on the TB than if it were closer.

I'm not sure if it matters, I just always wondered their reason for having the BOV closer to the turbo.

 

E-Mail Inline Pro. I'm sure they will tell you.

 

The closer the BOV is to the turbo the faster it releases excess air...relieving pressure surge that much faster. I guess it isn't a big deal, but the more efficient the better.

 

The reason that its best as close the the intake manifold as possible is the flow of air thou the piping. The reason for a bov is to prevent back pressure on the turbo (everyone knows this), so if the air flows towards the intake manifold then when the value is open (throttle closed) then all the air the the piping will be rushing out.
Now if you place the bov before the intercooler (or right after the turbo) then some of the air will have to travel back, fighting flow, and make its way out through the bov. Remember, we're right to prevent back pressure, but when you place the bov near the turbo your actually making more back pressure per-inch of piping.

This is what I have known when I had my 240sx Turbo'd... Since there was a difference with the early JDM engines for the 240sx is that the BOV was right there on the hot side... With the later JDM engines (the one i had) had the BOV on the cold side...

 

If it bothers you, you can run a BOV on both sides.

 

This is not correct. No fluid (air is a fluid) flows in a pipe like that. At any given point in the flow path, flow is only going in one direction. There are pressure waves and the like going in other directions though. Of course flow is inversely proportional to the resistance offered by the flow path, and dirctly proportional to the differential pressure across the flow path.

Once the BOV opens, its dump tube becomes the common leg of a TEE, fed by comingling flowstreams from the compressor outlet and from the air trapped behind the throttle. The space trapped between the BOV outlet and the closed throttle doesn't have to blow down immediately, unless the sensing point for the pressure line tied to the BOV's actuator diaphragm is also located in this section downstream of BOV. Even then, I doubt that it would have much trouble "blending in" with the compressor outlet flow to BOV dump, and/or to the engine through the throttle body.

I don't think that changing BOV outlet placement anywhere on the charge pipe would make any real measurable difference in performance at the speed the air is moving. I believe that space and packaging considerations determine placement of BOV. If you are recirculating BOV back to compressor inlet, then BOV should be downstream of intercooler, to prevent overheating.

The real purpose of a BOV is to prevent the turbo compressor from operating to the left of the surge line. Any centrifugal compressor operated in this unstable region will destroy its thrust bearings (at least) eventually. BOV does this by opening up an alternate to the normal flow path (when it is restricted by a closed throttle body).

If you are making boost and close the throttle, the compressors output backs up and stalls (or dead-heads) against the closed throttle body. Compressor outlet pressure climbs and flow drops. This pushes you up and left on the performance curve, towards (or past) the surge line (which slopes lower left to upper right).

Once BOV opens, the alternate flow path relieves pressure buildup (moving you down on the curve) and restores flow (moving right on the curve).

 

The goal of a BOV is to release pressurized air present in the intake charge piping (the air volume between the compressor outlet and the throttle body) when the throttle body is closed or near closed. BOV's are not 100% necessary, however. Most turbocharged race cars don't even use a blow off valve. Non of InlinePRO's race cars use blow off valves.

The BOV is much more applicable (and necessary) on a daily driven street car where long compressor life is essential. The quicker the pressurized air is released, the less chance there is for compressor surge. By locating the BOV closer to the compressor outlet, the local pressure in that region will decrease faster than if the BOV was located on the other side of the intercooler.

 

This is a lot to do about nothing. Mine is mounted after the intercooler. It works fine. InlinePro's is mounted before the intercooler. It works fine too. So what's the big deal?