I read in another recent thread that using a simple bleed valve on the wastegate actuator can bump the stock boost level on 850 turbos up to as much as 14 PSI! As far as I know, the 850 turbos have always relied heavily on the ECU to control boost, that's why we have the proliferation of chipping upgrades for this particular model. So my question is this: Has anyone else gone with just a simple bleed valve and had great success on this model? If so, please speak up!

As far as I know, bleed valves don't work on these cars. I have heard that the pre-96 850s may be a possibility (ie the T5R and earlier).

I have made the tweak on my 94 854 Turbo with a commendable increase in performance. My car has 169000 miles on the clock and I figured that it couldn't hurt to try. It took 15 min to do and I did not get my hands dirty. I shortened the shaft by 4 turns and felt a difference at low RPM driving in town. The motor seems to pull a wee bit harder from idle to redline. It could be mental, or it could actually have helped. I know this car well enough to tell the RH and temp outside by the way the car performs. I did feel a difference, just not a huge one. As far as 14 PSI, I have heard that 10 was pushing the comfort limits. I plan on going back with a calibrated pump/vacuum and setting mine for 9 PSI. According to what I was told, 4 turns is about 6-7 PSI. Volvotuning.com has great details on how to do this mod, and comes from a reliable source.

Prospero

A bleed valve and the rod shortening are two different mods. By shortening the rod you are cancelling the Volvo driveability 'boost ramp up'. By fitting a bleed valve you are trying to theoretically increase max boost. There are differences in the way the car behaves between these two mods despite the apparently same effect (a group of us learnt this when running a production racing car in the late 80s).

I'm interested in the rod shortening idea, however I have doubts it is such a good idea on FWD manuals. Having said that I have no doubt there would be a difference. Just wondering if it works on 96-on vehicles...

Aussie Pete wrote:

> A bleed valve and the rod shortening are two different mods. By

> shortening the rod you are cancelling the Volvo driveability 'boost

> ramp up'.

My car was built in 1994, I do not think that it has the updated (95+) software. (Yet) Also, I am unclear on how the ECU controlls the turbo as there does not appear to be any logic-based control on the "pneumatics" on the turbo and related valves/ actuators. Am I missing something here? This is my first turbo, so I could have things all screwey...

> By fitting a bleed valve you are trying to theoretically

> increase max boost. There are differences in the way the car behaves

> between these two mods despite the apparently same effect (a group of

> us learnt this when running a production racing car in the late 80s).

Would you care to shed some much-needed light on this for me, please? I think that I understand the idea, but still not 100% clear on how this system works.

Thanks

Prospero