Replacing blow-off valve?

[delicat]

Has anyone done this yet?

Mine is very week, it keeps blowing off at 10-11psi while the stock Delica valve should go off at 15psi from what I've read. It's one of the mods I've never done on my previous turbo vehicles so I wouldn't know where to start. Is there different options? Quality/price models...

Thanks,
David

[Green1]

I can't be positive, but I thought the stock one was supposed to be about 10PSI... people have talked about increasing their boost to 15 though...

[Jaz]

I'd probably opt for an earlier subaru wrx one - it's set for about 15 or 16 psi, cheap to come by, innocuous looking in that it's black plastic and small, and doesn't make a sound when vented back into the intake. It all just depends on whether they would work with however the Delica's system is set up.

[delicat]

Thx Jaz, I'll have to take a look at the wrx.

Green, from reading on the uk and Aussi forums the stock pressure is 12psi so the blowoff valve would have to be higher. If I recall it was 15...

Sounds like I'll have to take mine apart to understand it!

[lrp374]

I just increased my turbo pressure this weekend and my Blow-Off valve has started to open on turbo pressure. Seems to be about 13-14 psi. I thought I'd just replace it with a higher value until I started looking @ what it's for. Now I'm confused. It sounds to me like it should operate most times you go from wide open throttle to idle. Videos of cars show them operating all the time and they even put trumpets on them so everyone knows they are blowing off. I found the attached on WIKI put I'm not sure I'm any wiser.
Have you taken yours out yet Delicat?


Larry

[Green1]

I'll preface the following with a bit of a disclaimer... I'm not an expert on turbos or race cars, however the following is my understanding...

Under normal circumstances the blow-off valve works as sort of a safety to prevent over-pressure, it will open if your turbo is generating more boost than you are using. On our vehicles this should be pretty rare as the turbo is only generating boost "on demand".

However, because turbos have what is known as "turbo lag", meaning that when you floor the accelerator, it takes a moment for the turbo to spin up and give you any useful boost, high performance race vehicles avoid the lag by keep the turbo spinning the whole time, as a result they are frequently generating more boost than they are using, the result is the blow-off valve is constantly being used to vent the extra boost. (if you ever watch rally sport you will hear the blow off valves constantly venting, every time they let off the accelerator)

[delicat]

No, I haven't replaced mine yet and yes, Green1 got a good understanding of how they work. If for whatever reason the turbo was to malfunction and overboost without a blow-off valve the extra pressure could damage both turbo/engine. Hence the blow-off valve that will open within a specified range, in our case 15lbs of boost.

Mine still annoys me but I annoy my wife even more with all my Delica related outings... So I'm very selective as to where I spend my Delica moments...

It will get done, one day!

[lrp374]

I read some more and the attached info below makes sense. The first stuff I sent really only applies to gasoline engines which have a throttle valve. Diesels do not. Now I believe that the Blow-Off is simply an overpressure device to limit turbo boost. Now all I need is a solution.

[jessef]

It will get done, one day!

If I had a dime for everytime I said that ...

[Green1]

Well... the article misses 2 key points...
1) our diesels DO have a blow-off valve.
2) every diesel I have ever seen provides immensely more engine brakeing than the equivelant gasoline vehicle.

[delicat]

Ok, turns out our Delica don't have a blow-off valve. What they have is a pop-off valve! Confused?

Green1 explained it quite well:

However, because turbos have what is known as "turbo lag", meaning that when you floor the accelerator, it takes a moment for the turbo to spin up and give you any useful boost, high performance race vehicles avoid the lag by keep the turbo spinning the whole time, as a result they are frequently generating more boost than they are using, the result is the blow-off valve is constantly being used to vent the extra boost. (if you ever watch rally sport you will hear the blow off valves constantly venting, every time they let off the accelerator)

And the above doesn't apply to us. What we have is a simple safety valve (which is common on diesel engine) that will release the pressure if the boost becomes too high for whatever reason. I called a few Diesel Performance shop and that's what I got from them and NO, they didn't have replacement unit for our application.

So I'll have to take mine apart and see how it works (replace with a stronger spring or replace with a used unit).

D.

[LeeHammy]

Thought I would re open this topic.. have a watch its a good intro to the topic.

http://www.youtube.com/watch?v=Z_fG_b65WiU

Pajero 2.8L Turbo Max Boost Pressure is 13.7psi
Waste Gate Operation Pressure 12.9psi

Even if you are getting this boots you may be leaking and not holding your boost pressure as you will see int he video. (going to get a boost gauge) I am thinking of blocking off my dump valve (cant remove it it looks to be built into the intake manifold) and installing a blow off valve where the EGR used to be on the inlet manifold. Then I can adjust to make my boost exactly what is required or if I am daring I can up it a bit. I am also thinking of not venting into the intake of the turbo just so I don't add any more heat. But I also dont want to be made fun of for having a whooosh every time I reach max boost and change gears. I might just keep the EGR blanked off and put my blow off in the intercooler hose then I wont have to worry about a catch can or any crap blowing all over or if I want to dump it back into the turbo intake it will be the same clean air it is mixing with. Your thoughts?