sand_man

Okay, don't throw old "Sandy" under the bus. I've been dancing around this stoooopid mod since I brought my car home. Finally, I think I've got to do something. Spool seems a tad off and throttle response could be better. Even though I rebuilt my BOV assembly when I was in for an engine rebuild, I think that's the culprit.

To re-cap, I've got a B&B "short-neck" intercooler - obviously sitting on top of this ultra-behemoth hunk of a BOV/Diverter/Re-circ. housing!!!

My original thread:
https://rennlist.com/forums/911-turbo-930-forum/259339-965-style-blow-off-valve.html

My plan:
I thought about cutting up my BOV housing and welding up the openings to retain my B&B short neck intercooler. Truth be told, I will eventually be going with a 964 C2 Turbo intercooler, so it just doesn't make sense to spend any time on fab work while butchering these parts. I plan to keep the assembly as it is, jam the re-circ. valve shut with a rod (rendering it inoperable). I'll then fit the newer style C2 Turbo CIS elbow with a "modern" diverter valve on top. That way, when the time is right, I can just ditch the entire unmolested factory BOV assembly.




Any thoughts?

JFairman

I've thought of doing the same thing...
A piece of broom handle or dowel rod cut to length in place of the spring in the origonal BOV would probably work.
A more elegant way to do it would be to find an dead old fuel level sending unit from the gas tank and use the outer aluminum tube or something similar and cut it to the correct length and put it in place of the spring and spring guide to hold the piston in the shut position..
A piece of PVC pipe would work too.

Of course you have to plumb the origonal electric boost guage sending unit and overboost switch into the intercooler if you're using them.
Garretson/Andial intercoolers have an extra unused, capped off hose fitting on them already which may flow enough air for the new BOV valve.
It also may be possible to "T" into the aux air valve hose. That wouldn't hurt the aux air valve funtioning which only passes air when the motor is cold or warming up.
You shouldn't be on boost when the motors cold anyway.
Just don't know if those hoses have a big enough inner diameter to flow enough air for the new BOV.

sand_man

Here's a picture for those who aren't sure what the factory BOV housing looks like (not mine):

sand_man

A question regarding hook-up:

Being that I'm keeping the factory BOV assembly in place, and that I don't have a location on my intercooler to vent the other end of the C2 Turbo valve to, can I vent it to a connection on my existing housing or manifold...there are several places that I have blocked off? And can I T-off of my wastegate actuation line for the the C2 valve actuation line...the small connection on the top of the valve?

kellcats521

I did this mod over last weekend to refit the stock IC with the C2 BOV. I cut the diverter just after the ~3/4" port that is on the underside of the diverter - keeping the port and the boost gauge sending unit on the TB end. Then I cut a rectangle section out of the diverter side of the unit and TIG'd it over the opening where I cut it. Last, I cut out the threaded mount for the boost cutoff switch (mine had a stock looking helicoil in it) from the diverter side and drilled a hole on the TB side and TIG'd it in. The port on the bottom goes to the BOV, and the vac line that went to the diverter now goes to the BOV. I'll take better pics this weekend with the IC removed, but here's a dark pic of the TB end installed.


One thing to remember - I wasn't skilled enough to mount the B&B long neck, so any 'high end' fabbing I've done like this should prolly be taken with a grain of salt....

sand_man

AWESOME, kellcats!!! Thanks much for the picture...if it's not too much trouble, yes, some additional photos would be great! Not to wind you up, but it must have killed you to be fitting the factory hunk (BOV and intercooler) back on!!! Your thread regarding B&B ought to be made into a "sticky" at the opening of our forum!

sand_man

Don't laugh at me. I like to understand how things work. What was throwing me off was the concept of engine vaccum *AND* a turbo. I keep thinking in terms of pressure, being that the turbo is a compressor. So I was lost, now I'm found...I love you Wikipedia - science for the rest of us!

Any way, I thought I'd update my thread with a few diagrams in case someone stumbles onto this, while searching.

FWIW, the vaccum actuation line for the diverter valve must be *AFTER* the throttle plate...so I'll just use the line further down on the "pancake" manifold.
http://en.wikipedia.org/wiki/Blowoff_valve

Simplified, generic diagrams:

PorschePhD

Here is one I finished up on Mon. If you have a question shoot away.

sand_man

Looks great, Doc and thanks for sharing the pics. What you and kellcats described earlier is exactly what I pictured. Right now though, I think that might be more work than is worth and I'll just keep the entire honken assembly intact and render the valve section closed.

Without knowing what intercooler is being used, the only question I'd have is what is feeding the inlet of the C2 diverter valve? And on this project, what is being used as the vacuum source (skinny fitting on top of the valve)?

rsrfan

Stephen,
can you pm me with a price to perform this modification if I supply the factory assembly?

Thanks much,

JP

PorschePhD

Sand man,

It is not really that hard. All you need to make sure you have handy is a Tig welder or someone that can do it for you. Cut the end, measure it up and use the rest of the BOV assembly to cut the other square and tig away. Drill a hole, cert or tap it and that is good to go. The port to the BOV will come off the intercooler. It should vent back into the intake to avoid the plate slapping closed durnign shifting. Many times I will simply tig a snout in the new neck and vent the valve back in that way.

kellcats521

The vac line feeding the BOV that I used is the one that used to go to the vacuum booster/diaphram which is part of the diverter - it does originate from below the throttle plate, and I simply plumbed it to the BOV rather than plugging it. The 3/4" port and hose attached to the bottom of my cut assembly is the recirculation for the BOV - since that port already exists on the bottom of the diverter, I just cut it far enough down to include it on the side I'm using. So, mine is a bit longer than the one Stephen pictured, but I essentially did the same thing in that I used a piece of the remains of the diverter to make a cap for the section I'm using. I'll post pics over the weekend..... For reference, if you look at Sandman's pic of the dirverter, I cut it at the '180' of the part # stamping to keep/use that port on the bottom for the BOV recirculation.

sand_man

After much thought and encouragment from the good Doctor and kellcats, I think I'll cut this folker up after all! We'll call it my middle finger to Porsche's over-built assembly!!! To be honest, it almost pisses me off to think about how large this gawd damn thing is!!!!

Should'a bought a 965...

spuggy

I got a C2 BOV with a Kokeln intercooler setup. I took a couple of looks at the plastic Bosch valve and bought one from Forge Motorsport.

sand_man

My Hyperboost compressor by-pass valve (diverter valve) will be here on Friday...I got the "stealthy" looking black one:

http://www.stratmosphere.com/hyperboost.htm
The Forge is nice too...I got a good deal on this one, though.