Blow off valve

[Parksy10]

Hi can anyone tell me how to change the diverted valve I can’t seem to find it without taking too much apart. Any idea if I can do it or will I be better to take it to a garage. It’s a 2015 c250 coupe. Thanks

 

[LostKiwi]

What do you mean diverter valve?
If you mean wastegate I'm pretty sure you don't have one as your turbo is variable vane.

 

[Parksy10]

What do you mean diverter valve?
If you mean wastegate I'm pretty sure you don't have one as your turbo is variable vane.

No it’s the blow off valve on the intake side

 

[Lee Edwards]

I see some people describe the engine crankcase breather as” blow off “ . the breather is an easy change if you wish to attempt yourself. There are lots of videos of this on the web. Can you say why you think you need to change it ?

 

[Parksy10]

Do it’s the same as a dump valve. I read that it increases boost by forcing air back in to the turbo

 

[LostKiwi]

No it doesn't.
Boost is controlled by the ECU operating the variable vanes on the exhaust turbine.
The valve you're referring to as s blow off valve actually operates as a priority valve and only becomes effective when the throttle pedal is suddenly released. It then dumps boost pressure back into the inlet to prevent boost on the inlet stalling the compressor thus enabling the turbo to maintain shaft speed and spool up quicker.
This only happens when the throttle is rapidly closed such as on a manual gearbox when changing gear or when coming off and on the pedal quickly while driving in a spirited manner (but even then if you're a fast smooth driver those changes in throttle are usually slower).
Fiddling with it will do 2 things - make it louder (like some chavved Halfords turbo rice burner that goes pssst psst psst at every gearchange) and make the turbo lag increase.
One is annoying for everyone outside and the other annoying to you as a driver.

If you have an automatic gearbox messing with it will have next to no effect at all other than introducing lag.

You won't increase boost or performance.

 

[Parksy10]

Thanks I have seen mixed reviews I just thought for £90 and three screws it wouldn’t hurt to try since it can easily be returned to stock but I can’t even find the thing

 

[LostKiwi]

I really wouldn't bother.
Just to add to the above, if you vent boost to atmosphere you're venting air that has already been through the MAF sensor. When you lift off and then put your foot on the accelerator again the air the ECU has seen go through the MAF sensor is no longer there, so when the ECU injects fuel it runs very rich which can screw with plugs, valves, pistons and catalytic converters. Often you'll see a big puff of black smoke as a result.
I'd put the £90 to a decent remap if you want more power.

 

[Parksy10]

Thanks much appreciated i was wanting to make a few other mods before having a map so they could be taken in to account. I’ll take your word for it and just take it back. Thanks for taking the time. This is the first car i have owned that’s worth doing anything to and it’s the first Mercedes I’ve owned

 

[V6Matty]

In all honesty other than a good stage 1 map there is little worth doing to a diesel, unless your going to upgrade the turbo, injectors, fuel pumps, exhaust and then map your really just throwing money where it could be better spent on a more powerful 6/8 pot anyway

 

[LostKiwi]

In all honesty other than a good stage 1 map there is little worth doing to a diesel, unless your going to upgrade the turbo, injectors, fuel pumps, exhaust and then map your really just throwing money where it could be better spent on a more powerful 6/8 pot anyway

I think it's a CGI Matty.

 

[V6Matty]

I think it's a CGI Matty.

I was going by his previous thread on remapping

 

[LostKiwi]

I was going by his previous thread on remapping

Ah - well spotted!
In that case a blow off valve/dump valve has even less effect!

 

[Srdl]

I think it's a CGI Matty.

I was going by his previous thread on remapping

It’s CDI
https://forums.mercedesclub.org.uk/index.php?threads/c250-cdi-remapping.180780/

 

[Parksy10]

To be fair I’ve just spent 17k on it so I won’t be getting a 6/8 pot any time soon.

 

[flowrider]

I thought this was going to be a thread about flatulence

 

[ObsessionSA]

No it doesn't.
Boost is controlled by the ECU operating the variable vanes on the exhaust turbine.
The valve you're referring to as s blow off valve actually operates as a priority valve and only becomes effective when the throttle pedal is suddenly released. It then dumps boost pressure back into the inlet to prevent boost on the inlet stalling the compressor thus enabling the turbo to maintain shaft speed and spool up quicker.
This only happens when the throttle is rapidly closed such as on a manual gearbox when changing gear or when coming off and on the pedal quickly while driving in a spirited manner (but even then if you're a fast smooth driver those changes in throttle are usually slower).
Fiddling with it will do 2 things - make it louder (like some chavved Halfords turbo rice burner that goes pssst psst psst at every gearchange) and make the turbo lag increase.
One is annoying for everyone outside and the other annoying to you as a driver.

If you have an automatic gearbox messing with it will have next to no effect at all other than introducing lag.

You won't increase boost or performance.

Sorry, but you are wrong on a couple of fronts. You are saying it dumps boost preasureback into the inlet to prevent boost on the inlet. Well that is not what a dumpvale does, and in the case of stock vehicles this would be a recirculation valve( these are made to comply with noise rules, and keep also a vehicle quite).

You see what a dumpvalve recirculation valve does is safeguard a turbo, remember a turbo can spin up to 100000rpm, and when the throttle closes that turbo is still spinning, and there is still boost, so when that happens it creates back preasure on your turbo ( which is trying to slow down ) and that is where you can get turbo shudder( litteraly the compressor vanes shuddering) and where you get turbo flutter). So a dumpvalve is there to "dump" that preasure so this cannot happen. Nothing to do with keeping preasure.

Secondly a dumpvalve will never INCREASE lag, but in actual fact decreases it as agai, no back preasure on the turbo to rapidly slow it down.

Only way it can increase lag is if it has a seal leak somwhere...

I have noticed that on this forum and others that a majority of ppl have no clue what a dumpvalve and recirculation valve does...

 

[ObsessionSA]

No it doesn't.
Boost is controlled by the ECU operating the variable vanes on the exhaust turbine.
The valve you're referring to as s blow off valve actually operates as a priority valve and only becomes effective when the throttle pedal is suddenly released. It then dumps boost pressure back into the inlet to prevent boost on the inlet stalling the compressor thus enabling the turbo to maintain shaft speed and spool up quicker.
This only happens when the throttle is rapidly closed such as on a manual gearbox when changing gear or when coming off and on the pedal quickly while driving in a spirited manner (but even then if you're a fast smooth driver those changes in throttle are usually slower).
Fiddling with it will do 2 things - make it louder (like some chavved Halfords turbo rice burner that goes pssst psst psst at every gearchange) and make the turbo lag increase.
One is annoying for everyone outside and the other annoying to you as a driver.

If you have an automatic gearbox messing with it will have next to no effect at all other than introducing lag.

You won't increase boost or performance.

this is a short explanation, and as you can see a recirculation valve actually will have more lag than compared to a dumpvalve, but both does the same job.

on a diesel you can go DV route , although it is not as straight cut as with a petrol car, and whith using a DV you can gain a better response on throttle than what one had with the stock recirculation valve.

also good to mention is that you can sometimes set DV tension so that if somehow one overboosts for whatever reason your DV can open under boost and bleed off boost( i have personally used this method of boost controll on 2 of my drift cars when i had external waitgates malfunction).

 

[LostKiwi]

Sorry, but you are wrong on a couple of fronts. You are saying it dumps boost preasureback into the inlet to prevent boost on the inlet. Well that is not what a dumpvale does, and in the case of stock vehicles this would be a recirculation valve( these are made to comply with noise rules, and keep also a vehicle quite).

You see what a dumpvalve recirculation valve does is safeguard a turbo, remember a turbo can spin up to 100000rpm, and when the throttle closes that turbo is still spinning, and there is still boost, so when that happens it creates back preasure on your turbo ( which is trying to slow down ) and that is where you can get turbo shudder( litteraly the compressor vanes shuddering) and where you get turbo flutter). So a dumpvalve is there to "dump" that preasure so this cannot happen. Nothing to do with keeping preasure.

Secondly a dumpvalve will never INCREASE lag, but in actual fact decreases it as agai, no back preasure on the turbo to rapidly slow it down.

Only way it can increase lag is if it has a seal leak somwhere...

I have noticed that on this forum and others that a majority of ppl have no clue what a dumpvalve and recirculation valve does...

Sorry, but you are wrong on a couple of fronts. You are saying it dumps boost preasureback into the inlet to prevent boost on the inlet. Well that is not what a dumpvale does, and in the case of stock vehicles this would be a recirculation valve( these are made to comply with noise rules, and keep also a vehicle quite).

You see what a dumpvalve recirculation valve does is safeguard a turbo, remember a turbo can spin up to 100000rpm, and when the throttle closes that turbo is still spinning, and there is still boost, so when that happens it creates back preasure on your turbo ( which is trying to slow down ) and that is where you can get turbo shudder( litteraly the compressor vanes shuddering) and where you get turbo flutter). So a dumpvalve is there to "dump" that preasure so this cannot happen. Nothing to do with keeping preasure.

Secondly a dumpvalve will never INCREASE lag, but in actual fact decreases it as agai, no back preasure on the turbo to rapidly slow it down.

Only way it can increase lag is if it has a seal leak somwhere...

I have noticed that on this forum and others that a majority of ppl have no clue what a dumpvalve and recirculation valve does...

What I said is correct.
You didn't interpret it correctly.
In a normal petrol car the dump valve sits between the turbo and throttle part of the inlet tract.
Rapid closing of the throttle can lead lead to high pressure in that section of the intake.
The dump valve vents that pressure to atmosphere (open dump valve) or back to the low pressure side of the turbo (closed system or what you called recirculation valve).

A dump valve and recirculation valve are the same thing. The only difference is whether it vents to open air or turbo inlet tract.

The purpose of it is to prevent compressor stall where the exhaust flow is insufficient to overcome the higher pressure in the high pressure side of the turbo. A Smart turbo has a waste gate but no dump valve. You can hear the turbo make a distinctive chirrup as the excess pressure post turbo bleeds back through the compressor when the throttle is closed.

 

[ObsessionSA]

What I said is correct.
You didn't interpret it correctly.
In a normal petrol car the dump valve sits between the turbo and throttle part of the inlet tract.
Rapid closing of the throttle can lead lead to high pressure in that section of the intake.
The dump valve vents that pressure to atmosphere (open dump valve) or back to the low pressure side of the turbo (closed system or what you called recirculation valve).

A dump valve and recirculation valve are the same thing. The only difference is whether it vents to open air or turbo inlet tract.

The purpose of it is to prevent compressor stall where the exhaust flow is insufficient to overcome the higher pressure in the high pressure side of the turbo. A Smart turbo has a waste gate but no dump valve. You can hear the turbo make a distinctive chirrup as the excess pressure post turbo bleeds back through the compressor when the throttle is closed.

Mmm...you know alll turbos has wastegates. Most internal. Others ( like the precision setup we run on the drift cars ) does not have internal. That is why we use external waste gates...


And the waistgate has absolutely NOTHING to do with the dumpvalve...a waistgate bleeds of exhoust gasses to the hot side of the turbo and that is how boost preasure is regulated..

Internal waistgates has limitations so then we weld them up and use external gates.

So again, wasitgate and dumpvalve is two completely different things..

But as i also mentioned , when i had a waistgate failure i have before loosened the tension on my DV therefore under a certain amounf of preasure it would open UNDER preasure and as a bushfix on track to keep boosy preasure in check it can work..

So again it CANNOT ever affect lag..but CAN effect boost preasure if not set correctly and or defective seals and springs...

The argument here from the beginning is that you say it produces lag and los of power...wich is completely false unless in the scenarios i have mentioned..

Easy hey..