C2 style bypass valve that's closed @idle/low rpm?

[john walker's workshop]

The C2 turbo bypass valve sucks unmetered air @ idle. Is there a good aftermarket valve that stays closed @ idle and low rpm unboosted cruise, and opens with higher vacuum on higher rpm closed throttle shifts? Maybe one that's adjustable to do that? My '87 project.
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[sigchuck]

I thought the c2/964 turbo valve operated on a closed circuit as a Re circulation valve, not like a typical BOV. Is the valve defective, or is that standard operation? Mine is plumbed to Intercooler and air meter boot, with vacuum connection to throttle body, so I always assumed it was all metered air.

[john walker's workshop]

Hooked to below throttle vacuum, which opens it at idle. Dumping to atmosphere at the moment due to stock intercooler with no port to run it to. New valve, C2 elbow. Drops idle drastically if I put my thumb over it. It sucks air. I'm about to run without it until I find an adjustable unit that only bypasses on higher rpm off-throttle.

[john walker's workshop]

Any more input?

[1Bad86]

I just switched to the same set up and it's causing some issues on my end as well. (Just posted on my thread last night "fuel injector issues and other dilemmas" ).
Yes, venting to atmosphere you'll have and feel a vacuum leak and the idle will drop when you cover it.
I ran a hose over to an unused port in my IC (Andial) to recirculate.
My car is basically shutting down for 3-4 seconds between shifts no matter how I route the valve.
I'll post more details on my thread later.

I should have just left it alone since everything worked just fine before but hey what's the fun in that lol.

An adjustable unit is probably in my near future as there's no going back now.

[RarlyL8]

There were a few threads on this several years ago, here is one.

https://forums.pelicanparts.com/911-930-turbo-super-charging-forum/797421-variable-boost-bov-settings.html

.

[john walker's workshop]

Still looking for a bypass valve that is adjustable with springs or shims that is a direct replacement for the C2 930 plastic POS. Any recommendations?

[Dr J]

This is what I suggested on the x-post in the tech area

https://forums.pelicanparts.com/12130717-post5.html

[spuggy]

Originally Posted by john walker's workshop

Still looking for a bypass valve that is adjustable with springs or shims that is a direct replacement for the C2 930 plastic POS. Any recommendations?

I held the Bosch 965 valve in my hand for about 30 seconds before going "yeh, no" and heading to Flea Bay for a aftermarket one... Ended up with a Forge Motorsport one for about $100 (they're very much pricier now it seems)... Worked great for me, never adjusted it. I would peer inside it every 3 years or so to check the grease hadn't dried out and just button it back up...

Same Bosch valve used on VW, Audi, SEAT, so many, many choices. If it looks the same arrangement as the factory valve, very likely a direct replacement. Most come with different springs and/or shims. They're all over Flea Bay, eg (random selection, haven't seen/used any of these - they're very simple devices):

VW Audi billet 1.8T 2.7T Diverter Valve BOV Black MK4 Jetta GTI GLI S4 97-06
Blow off Valve BOV Kit For MK4 Jetta GTI GLI VW Audi billet 1.8T 2.7T Diverter

TurboSmart ones are supposed to be good. Flea Bay might not be the best place to buy "name" brand items cheap (eg could get a knock-off).

You should be able to tune it to stay shut at idle, pretty wide range of vacuum between idle and overrun (18 mm/Hg to about 30 on mine). Then the concern would be dumping metered air to atmo instead of recirc'ing it - because CIS is still going to provide fuel for all the air it "saw" go past the AFM.

Plenty of guys quite like flameballs on the overrun, so this may or may not bother you, LOL...

Maybe use the overboost sensor hole for recirc? I ran without one for years - shouldn't really need it with a decent wastegate, or unless you suffer from boost creep...

Dr J's suggestion of a check valve also seems like a good one - but I've no experience (yet) with those as idly looking around for one to add an IAC (for warmup) without leaking boost. Can you recommend one Dr J?

[Dr J]

Originally Posted by spuggy

Dr J's suggestion of a check valve also seems like a good one - but I've no experience (yet) with those as idly looking around for one to add an IAC (for warmup) without leaking boost. Can you recommend one Dr J?

I got one like this from NAPA:

https://www.napaonline.com/en/p/CRB229000

[TurboKraft]

25mm replacement for Bosch/OE:

Haven't tried one of these yet because we haven't experienced the issue you're having, but we use a lot of Turbosmart products and haven't been disappointed yet:
Turbosmart Kompact Plumb Back Valve (Diverter Valve)

Here's the updated version of one we used a long time back, when we were replacing someone's failed aftermarket one (not naming names in case still sold by the host) with another:
Turbo XS RACING BYPASS VALVE TYPE 25

Forge was also a quality OE BOV replacement, but we haven't used one in 15+ years.