850 Blow Off Valves and Compressor Bypass Valves for the 850 Turbo

This is my first post like this so I hope I'm doing it right. I'm more of a Facebooker but I thought my experiences were much better off shared on a forum.

I've been playing around with blow off valves or "compressor bypass valves" on my 850R. I've got a Kinugawa blow off valve, an eBay copy of a HKS SSQV blow off valve and the OEM Volvo CBV.

The Kinugawa is rubbish, don't bother with this. The kit comes with 3 springs and it seems like good value for under $100 and with a straight forward installation. The design is nice, parts seem like good quality but it just doesn't work right. It is fully atmospheric. Even with the stiffest spring fitted the valve is opening at idle. This caused massive issues to the point where my car wouldn't even idle by itself. I tried shimming (stacking up washers on the spring) with the same results. I stacked up 2 springs (the stiffest and the medium rated one) with slightly better results but still I wouldn't rely on it.

The HKS SSQV blow off valve from eBay for a mere $50 actually performs quite well. I did get a bit of compressor surge letting off the throttle at low boost. Letting off at full boost it makes loud HISS! Like the car's in the first FnF movie, it gets annoying and it's very obnoxious. The only real down side is you have to block off the factory CBV and plumb in the HKS blow off valve somewhere (which involves moving some things).

And finally the OEM compressor bypass valve, the best option for best performance but none of that PSSHHH! noise. This is by far the only option I've tried that I can fully rely on. I know Forge make a billet aluminum "piston" version but it's god damn expensive.

In conclusion, the HKS SSQV blow off valve is the only atmospheric one you can use reliably but it will require a bit of work to fit. If you want true reliability and don't care about what sound it makes then stick with OEM. I will be testing something I found online shortly called an Intake Pressure Compensation Valve (by Forge, google it). I will try it with the stock CBV and the Kinugawa one to see if it improves anything.



  • @shew

    I bought this CBV from Kinugawa and it worked fine when fitted to my B230 running a 19t. Its a Non-atmospheric type:

    The turbo originally came with an atmospheric one and it caused drivability issues, like Lag/hesitation on and off throttle and also idle issues.

    Comparing the factory non-atmospheric CBV to Kinugawas CBV in the pic above, the Kinugawa one showed a noticeable increase in power and slighly less lag...

  • Oh, and it sounds great too.

  • carnut222Greg S @carnut222 Daylesford VIC
    edited October 2019

    Good info to know! Thanks for the write-up and maybe others will chime in with their experiences too. Only thing I know is I used a Bosch CBV (black plastic one - same as what’s used on some SAAB turbos) when I had the supercharger on our 240 and it worked well and was reasonably-priced back in the day.

  • ^^^ that Bosch item looks the same as the standard on that came on my little tt so replaced it for a forge one and very pleased with it . Slight woosh sound . So i changed the 850 R one for a forge one as well but being auto obviously its not a blow off . Recirculation ( think that's what it's called ) happy with it but i am thinking of changing the spring soon , it came with 3 springs and i think it has the softest spring atm . They are a bit of a bitch to get to though , did anyone take the heat shield off to get to it ? As i didn't so maybe thats the answer ...

  • shewSam @shew Sydney, Australia

    @ALVO360 That looks good. I think the whole issue is that mine was atmospheric.

    @carnut222 I had a Saab 9000 Aero, it had an amazing factory blow off noise!

    @rado That Forge one for the 850 is bloody expensive!

    I got my Forge intake pressure compensation valve in the mail today. It's an interesting idea which applies positive pressure to the CBV diaphragm on boost and then negative once off the throttle. I've got it set up with the standard CBV at the moment but will try my kinugawa atmospheric one on the weekend. Didn't get to go for a test drive, too late and car is too loud haha

  • My old forge dump valve, changed it to a recirc one when I shipped it to Oz to get through compliance

  • shewSam @shew Sydney, Australia

    @Jamest5r_ did you have any issues with it opening at idle and sucking air?

  • Ex850RSnoopy @Ex850R Somewhere Over the Rainbow. Melbourne.

    Sounds like you have it plumbed in wrong?

    The hoses off the TCV may have been wrong before you got the car so confusing the issue?

  • shewSam @shew Sydney, Australia

    @Ex850R the CBV vacuum line comes straight from the intake manifold, correct? Has nothing to do with the TCV.

  • Ex850RSnoopy @Ex850R Somewhere Over the Rainbow. Melbourne.
  • shewSam @shew Sydney, Australia

    I've seen that diagram many times. I believe my TCV is correct although the numbers on the diagram don't tell me a single thing because I've got an ipd TCV.

  • @shew snoopy is confused cbv is straight off manifold nothing to do with tcv.

  • shewSam @shew Sydney, Australia

    This little Forge doo-whacky is incredible! I'm now running the Kinugawa blow off valve which I hated, with the medium rated spring and it's working perfectly! Bring on Nationals.

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