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I need to know if my blow off valve may need adjusting? I have a blow through turbo 1915 rail buggy and at idle when you look in the hole in the side of the blow off valve you do not see the valve opening or "fluttering" at all. Is this normal, or do I need to loosen it up? I have friends that have ton of experience working on turbo engines, but not VW rail blow through turbo engines. They seem to think it should be opening some at idle. As far as hearing it blow off when getting on it and letting off at higher rpms, I can hear it slightly but it isn't that loud. What are your thoughts? Any advice would be appreciated. Not sure if it matters I am running dual Weber carbs and have a K&M Air Intake.

Your engine might have a bigger cam in it and not have a lot of vacuum at idle.
The critical time is when you let off the throttle after boosting and you really can't replicate that just sitting in the garage revving it.
Put a Mighty Vac on the fitting and see how much vacuum it takes to pull it open.
When you are at full boost and pop the throttle closed is when it needs to work.

I use an elcheapo Bosch plastic BOV and it works fine up to the 22 lbs. I have tested it so far. It has a one inch inlet and outlet which might be smaller than some of the after market ones.

It's pretty quiet at low boost but gets noisy at high boost.
Although it is only about 6 ft from my ears in an open Fiberglass Buggy.

Post a pic of your setup. Pictures speak volumes.........

FWIW, note that Porsche used those "cheap" Bosch plastic recirculating style BOVs for decades, from the original 930.
They may still.
I suppose you could use two if you need more airflow but a 930 could easily make ~450 HP in its later trims.

If set up as designed to recirculate back to the intake above the TB you might not even hear it work.
(if you run CIS or a MAF sensor it should return after the air meter, before the TB, although you might be able to return it to the plenum on SD, assuming fuel/spark cut work instantly on liftoff... Hm might work as anti-lag if you didn't cut fuel)

The reason they are "cheap" is that most European (at least) OEM turbo cars used them from the mid 70s, and they generally don't break, so they are common as hell used.

I'm curious how much pressure they'll hold.

Piledriver wrote:FWIW, note that Porsche used those "cheap" Bosch plastic recirculating style BOVs for decades, from the original 930.
They may still.
I suppose you could use two if you need more airflow but a 930 could easily make ~450 HP in its later trims.

If set up as designed to recirculate back to the intake above the TB you might not even hear it work.
(if you run CIS or a MAF sensor it should return after the air meter, before the TB, although you might be able to return it to the plenum on SD, assuming fuel/spark cut work instantly on liftoff... Hm might work as anti-lag if you didn't cut fuel)

The reason they are "cheap" is that most European (at least) OEM turbo cars used them from the mid 70s, and they generally don't break, so they are common as hell used.

I'm curious how much pressure they'll hold.

I'm definitely putting it to the test but I have found a few threads that mentioned the Bosch plastic ones were only good to 15 plus lbs if I recall correctly.
I have been above that for some time now. Not that I am on boost all the time because I'm not. It is a daily driver in the summer and I drive it like a White Man most of the time.

Thanks guys. We will try the shop vac approach. Really appreciate your input!

Not a shop vac but one of those small hand vacuum pumps.
Like this.
It has a gauge on it and you can just pump it a little bit to control your vacuum.

http://www.amazon.com/s/?ie=UTF8&keywor ... qx9cdutg_e

Which valve are you using? I put a Turbonetics Raptor valve on my Dodge Spirit, and the spring was so strong it wouldn't open up no matter how much boost I made. Not sure what the engineering reasoning is behind that, but the valve has to open to work! I found a better (much softer) spring at the hardware store, and now it opens like you'd expect. Mine doesn't stay open at idle, but stays open long enough to avoid damaging the turbocharger so I'm calling it good. You only need enough spring pressure to keep it sealed under pressure, because remember that the valve itself sees the same pressure on both sides of the diaphragm on boost.