Various questions about turbo (Boost PSI, Blow-off, etc.)
 

I own a 95 Volvo 850 turbo and I'm looking into messing around with the turbo. I just have a couple questions that will help in the process. What is the maximum PSI the stock turbo can produce? I have owned my car for 2 years now and the turbo just seems to not pull its weight anymore. I used to be able to pounce on the pedal around 2500 RPM and the car would take off, and recently it has been running at a low efficiency in my opinion.

The first thing I was looking into is a blowoff valve. My first question is, will a blowoff valve function the same with an automatic car as well as with a manual? I like that they sound cool but I have also been reading up on the benefits and it makes a lot of sense why they are used. Has anyone actually installed a BOV on their 850? Does the my 850 currently have a recirculating valve or nothing at all?

Also, I was thinking of a boost controller to bypass the wastegate and provide more boost more often. My only concern with that is the head gasket. The car is now 13 years old and I know it ain't good to blow a head gasket. Does anyone here have a boost controller on their 850?

Is there any other tweak to a boost that I am overlooking her? (besides an intercooler... too expensive)

I personally do not know the answers to your questions, but know it's been posted on here by tech and others. I would do a search, but do not have time right now. Try searching, cause I know the answers are here.

Safe boost to run is about 12 PSI. I would also get an ECU as well and you can run a little higher. I am running about 13 to 14 PSI on my Yellow one with an ECU and MBC.

The stick bypass valve works really good on these cars but you can put a blockoff plate on the factory bypass and run a BOV if you want.

I bought an ECU from a guy who owned the T5 model so I believe it will add more fuel if boost is increased automatically.

What ECU and what MBC are you using? It would really help as I am terrible at shopping around. Thank you

The new ECU will help, but it still has a fuel cut off. So you can only go to ~15psi before the cut out. Now since you will be upping the boost, It is highly recommended that you have a solid stage zero before you modify the car. Stage zero is basicly regular maintenance to get the car back from when the car left the factory.

The safest way you can goo about doing this is by a chip or an ECU upgrade. Both of these (chip or flash) have stock reliability and remove the fuel cut off so boost can be set higher.
Even the stock turbo ecu will adapte to the higher boost. If you need an MBC, I suggest http://www.boostcontroller.com/, they are a great company. And you will need an aftermarket boost gauge. Now like tech said, the stock CBV will be jsut fine for the level of boost you are running. If you go over 20psi, then that is where I would think about getting a better BOV.
Remember to run the highest octane you can find (91 US ~ 93/94 in Euro). and keep up on regular oil changes, with good quailty oils (like Mobile1, Royal Purple, Castrol ...etc.).

The stock turbo, should be a 15G, can boost 20+psi, but that is when the turbo starts to super heat the compressed air. A great option to help against detonation or pinging would be water/methanol injection. It will cool the charged intake air and will lower combustion temps. water/methanol injection is kind of exepensive (~$400-$1000).

These are just other options for you. Get a aftermarket boost gague, a MBC, and enjoy the fun of 12psi. If you want more then that, get the chip or ECU upgrade and go from there.

Good luck.

I am running an Upsolute tune and a MBC that was a decent made one a buddy had gotten me. He buys all of them from a guy in South Florida I believe.

I am also running one from a 96 car without air pump. So it also deletes the EGR on the car.

But if you can find an IPD or one of the other decent brands used I would try to get them.

The upsolute is a decent one and the one only one I have run but I hear the others are better.

I just put my BOV on and I haven't noticed a change in sound.

If I don't figure the sound issue tonight (as the BOV doesn't seem to be working) I'll order the blocking plate.


I wish I could find one that wasn't so expensive. Forge's is $40. It's a piece of metal....lol.

Here is the link to the most recent post actively going on here regarding MBC:

https://volvoforums.com/forum/volvo-850-16/just-bought-27124/