What fitting did you use to place next to the turbo?

A side effect of blow off valves that vent to atmosphere is during long decelerations like going down a hill intake manifold vacuum is high and so is the inside of the intercooler so the blow off valve is fully open but there is no turbo boost because the throttle is closed and the turbo has slowed way down.
The result is the blow off valve is under vacuum and starts sucking in unfiltered air that may be dirty depending where you're driving.
Some blow off valves like the 25 mm 964 turbo type recirculation type valves can be mounted to vent to atmosphere instead of into the rubber elbow hose and then you can install a small K&N type air filter on the end of it so it filters the air being sucked in when this happens.

With the very nicely made TIAL type blow off valves with the air exit slots around the sides there's no way to put an air filter on it.

I always thought the correct place to put the valve was close to the throttle since that was what I've heard from another thread here. The BOV on my 951 is located near the throttle, even the diverter valve on stock 951's are in the same place and it seems to work fine. On my 930, the BOV is located after the turbo and far from the throttle, and while it still opens at full boost, it still goes "fu-tu-tu-tu-tu", but "pssss" at 3000-4000 rpm.

The K.I.S.S. method is as outlined above, and same as in post #9's photo:
* 965 CIS elbow #930-110-382-00
* 993T diverter valve #993-110-337-51
* weld a 25mm tube on the outlet side of your intercooler

If you want to put one just off the turbocharger, weld a 1" tube to the charge pipe between the turbo and intercooler, plus a corresponding 1" tube in the fresh air tube going down to the turbocharger.


Or run two diverter valves, like we did on this setup for a high power CIS 930 with a turbo much bigger than a K27. On the mockup engine after fabrication:

http://forums.pelicanparts.com/uploa...1398272193.jpg

The factory put the valves in convenient locations. It still works, but not as efficiently. Jim, With the Tial you install the correct size spring that matches your engines vacuum, although it isn't 100% in all circumstances, it does limit the open times during deceleration. I'm not sure, but I think Tial is the only ones who offer different spring rates for their BOV's?
Gumba the best place on a 930 is the charge tube from the turbo to the intercooler. If you went a Tial for example, they can be ordered with a steel or aluminum bung for the valve.

There's no provision on the back of the intercooler for the diverter return line. The blue fitting is 3/4-7/8" thread size.
It looks like my only option is to go with a bov mounted on the charge tube above the bend at the turbo. Any other options other than tial?
Since I'm running 1.1 boost is there any particular spring? The car is street driven only, max power and shift point is 6,000 rpm.http://forums.pelicanparts.com/uploa...1398277138.jpg

Gumba, the spring value Tial BOV's have are determined by the vacuum value at idle. Tial has a chart that suggest what spring value to use and it is only based on vacuum. It has nothing to do with boost or RPM. If a diverted valve is used it should be mounted on the turbo to intercooler tube. But.... It has to Be plumbed back into the air Inlet tube. Some intercoolers, as Chris stated, have a 1" port on the back side. A diverted or BOV could be mounted there and either vented to atmosphere or to the air Inlet tube. It will work,
But ultimately the turbo to IC charge tube is the optimum location.

You can weld one 25mm bung/tube to the back (outlet) tank of the IC. Easy, connect to diverter valve with 1" ID hose.

Or weld on the hot side charge pipe.

The diverter valve on CIS engines is plumbed back to the compressor inlet because that air has already been measured by the metering plate, and fuel has been injected accordingly. The engine will run quite rich on closed throttle if you dump the air to the atmosphere. EFI can do as they please. I personally run the stock diverter.

It is extremely rare for a vacuum to be generated in the intercooler/boost piping on closed throttle. It certainly does not happen on a single turbo 930. Even a bypassed compressor makes a small amount of positive pressure. I concur that the bypass valve spring is chosen based on the idle vacuum.

The location in the boost piping is non-critical from a performance standpoint. Many modern turbo's have the bypass integrated right on the compressor cover, as this is a quieter location with simpler plumbing.

FYI, there are electronically controlled bypass valves that are very quick acting.

Thanks for all the input.
Moving onto the turbo. I have a K27 7006 on the car. It came with the car, and I have no idea what condition it's in.
Is there anything I should check for?
Is there a better turbo option based on the engine specs?
Is there anyone who can rebuild/modify this unit.
thanks.