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BOV & turbo questions

I'm not seeing a bov or diverter on my turbo. I'm looking at the photos in this old post:
Blow off valve vs. stock boost diverter
It looks like it should either be at the elbow before going into the cis, or some type of T connection coming off the elbow.

In regards to the turbo, the car came with a K27, but I have no idea which model, or age. Is there an i.d. plate somewhere on the turbo housing.

The motor had a complete rebuild in '09 by Jerry Woods when we lived in CA. So it has all the smog stuff in place, which I'd like to remove.
specs: 3.5 twin plug, sc cams, 12 plug distributor, SSI,s, DP intercooler & muffler, cis. 390 chp @.9 bar on their dyno.
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Harold
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'68 VW Turbo Crewcab
Old 04-22-2014, 09:09 AM
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Can you post a picture of your engine compartment - with and without the intercooler in place? There's really no way to answer your question otherwise.

The 3K (KKK) turbos have id plates on the compressor (cold side) housings - outside side, facing the left/driver's side of the car - near the top.
Old 04-22-2014, 09:46 AM
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Hey Gumba, I've had hands on a top-end rebuild of a Jerry Woods built engine. It had no BOV or bypass assembly. Maybe that's how they did them? Baffled the crap out of me that this car didn't have one...seems the factory thought it was important, right?
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Old 04-22-2014, 11:28 AM
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jwasbury,
They have they're own way of doing things. Hasn't been an issue, was curious. I can see on one of my shots with the motor out the turbo i.d. tag is at the top on the drivers side. It's a K27, just not sure of the model/vintage.
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Old 04-22-2014, 11:43 AM
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Quote:
Originally Posted by jwasbury View Post
...seems the factory thought it was important, right?
Sometimes yes, sometimes no.
The factory 930-S engines with the larger Ruf-like intercooler usually had no diverter valve.
I haven't seen diverter valves or pop-off valves on their later Turbo racecars, either -- none on the GT2 Evos.

Easiest would be to install the 965 CIS elbow which has a 25mm port for a diverter valve, use a 993T diverter valve, then weld a 25mm tube on the outlet side of your intercooler.
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Old 04-22-2014, 11:56 AM
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Is there any down side leaving it off?
The turbo is a k27 7006.
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Old 04-22-2014, 12:04 PM
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I've heard of folks ditching the BOV back in the day. But since the 964 BOV design it seems like no one would go without anymore. Who knows...
Old 04-22-2014, 12:29 PM
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Interesting. No BOV or bypass/diverter valve seems to fly in the face of conventional wisdom (well, Pelican-wisdom, anyway) that a BOV is important to prevent "turbo stall" (for lack of a better description). Gives all that pent-up pressure somewhere to go when the throttle is closed as opposed to back-feeding into the turbo compressor wheel, thus forcing the turbo to do things it doesn't like to do. Always learning something new here!
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Old 04-22-2014, 01:07 PM
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When I had my garrison aftermarket inter-cooler on my 77 3.0, it originally lacked a bypass / diverter valve. I did as Chris mentioned, I installed a 965 elbow and 993T diverter valve and welded a tube directly into the intercooler. It made a huge difference. Having the diverter valve installed smoothed out the transition between shifts. Boost came on more quickly and lag was definately reduced. Some have said the without a diverter, the turbo stalls out when the throttle plate closed between shifts. I concur.

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Old 04-22-2014, 01:20 PM
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Quote:
Originally Posted by gumba View Post
Is there any down side leaving it off?
The turbo is a k27 7006.
Not running a diverter/blow off valve causes compressor surge. Compressor surge happens when the throttle closes and the air from the turbo rushes back through the compressor wheel. It is often characterized by a loud "fu-tu-tu-tu-tu-tu-tu-tu-tu" noise whenever the throttle closes. Compressor surge from the complete lack of a diverter/blow off valve can lead to the damaging of the compressor wheel, which means costly repairs.

Also make sure your diverter/blow off valve is located as close to the throttle as possible. The blow off valve on my 930 Slant is located far from the throttle, so at its full 1.25 bar of boost, there's a little bit of surge, but at 3000-4000 rpm, it makes a nice "pssss".

The turbo on my car BTW is a T66, which is bigger than a K27, in case you were wondering

Just my advice on blow off valves
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Last edited by TheRedSlantnose; 04-22-2014 at 04:34 PM..
Old 04-22-2014, 04:31 PM
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^^^ Jason, for someone that seeks advice on such subjects as car washing and where to buy brake pads, you are surprisingly knowledgeable, and very well written, about blow-off valves!
Old 04-22-2014, 04:51 PM
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Quote:
Originally Posted by Ronnie's.930 View Post
^^^ Jason, for someone that seeks advice on such subjects as car washing and where to buy brake pads, you are surprisingly knowledgeable, and very well written, about blow-off valves!
I just seek advice on stuff I don't already know or need recommendations for, but not exactly everything
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1987 930 Slantnose Cabriolet, 545 hp, Guards Red- Weekend cruiser
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Old 04-22-2014, 05:14 PM
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So which bov should I get?
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Old 04-22-2014, 06:34 PM
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while I'm at it, what plugs do I use to replace the smog lines.
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Old 04-22-2014, 06:38 PM
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Quote:
Originally Posted by gumba View Post
So which bov should I get?
Doesn't have to be a blow off valve, it can be a bypass (diverter) valve if you don't want the "psss" noise, but that's your choice. The one on my 930 is a Forge BOV, and my 951 has a TurboXS BOV. Both of them are good, but the one on my 951 is more responsive since it's closer to the throttle. The most common BOV I've seen, especially in high-performance upgrades is the Tial BOV. If you want a whistling noise, you can get an HKS SSQV BOV, but the HKS BOV isn't commonly used in Porsches for some reason.

When getting a BOV or bypass valve, be sure to check its maximum boost capacity because if you're running more boost than the BOV or bypass valve is designed to handle, the piston inside would be forced open at full boost, causing a sudden loss of power. Though seeing you're running a modest 0.9 bar of boost, I'm sure many BOV's and bypass valves on the market can handle that.

Good luck and have fun with your car!
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1987 930 Slantnose Cabriolet, 545 hp, Guards Red- Weekend cruiser
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Old 04-22-2014, 06:50 PM
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My mistake, I meant diverter valve as Chris suggested. I run the boost at 1.1.
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Old 04-22-2014, 07:57 PM
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Harold-

Use 914 caliper bleed bolts for the smog plugs, sold here.

Many run the OE Bosch 710N, but I'm not a fan - in my boosted Audi daze they'd ingest themselves. Bailey / Forge at the time made an aluminum 710N lookalike @ that time that I liked.

I'm sure there's a ton of good options these days tho. And me - yes - I'm more a fan of BPV than BOV... not a huge queef proponent...
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Old 04-22-2014, 09:33 PM
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Quote:
Originally Posted by gumba View Post
My mistake, I meant diverter valve as Chris suggested. I run the boost at 1.1.
In that case, many bypass valves can handle 1.1 bar, but you can still check the maximum boost capacity of the bypass valve just to be safe. You can also still get a BOV, but use a recirculation fitting.
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1987 930 Slantnose Cabriolet, 545 hp, Guards Red- Weekend cruiser
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2005 Toyota Tundra SR5 Double Cab 4x4, stock 282 hp, Silver- Daily driver
Old 04-23-2014, 04:12 AM
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Thanks guys.
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Old 04-23-2014, 04:45 AM
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Just a note a BOV and a diverter valve are technically the same thing. The difference is the Diverter has a provisions to plumb back into the intake where the BOV simply vents to atmosphere. There are some that have attachments that can be either or, but they are kinda ricey. Both valve types main purpose is protection to the Thrust bearing in the turbo and when placed right help recovery spool in between shifts. If either valve is placed close the the throttlebody, then boost recovery in between shifts is favored but thrust protection is limited. If the valves are placed closest to the turbo, "THE actual correct placement", It protects the thrust bearing AND allows in between shift boost recovery.
I like the 50mm Tial's I been running as they don't wheez like a maimed Peacock.
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Old 04-23-2014, 06:22 AM
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