Pierburg Valve

**AlfaJack** · 23-08-12, 08:40

That looks to be the same as I have. I think you wind it in for more boost (compressing the ball and spring.

That restrictor is a Q4 part which has was connected with the original pier-burg.

Where in Surrey are you?

**Alfa Patch** · 23-08-12, 14:38

Originally Posted by AlfaJack

That looks to be the same as I have. I think you wind it in for more boost (compressing the ball and spring.

That restrictor is a Q4 part which has was connected with the original pier-burg.

Where in Surrey are you?

I am based in Ham near Richmond and work in Esher.

The instructions say that the more i wind the screw in the more the boost will rise. I suppose its worth a go without the ball and spring before i just chuck it in the bin.

I have tried it with and without the restrictor and it honestly makes no difference.

Getting gradually more frustrated with burning myself making adjustments!!

**AlfaJack** · 23-08-12, 15:17

Damn...a bugger of a journey away to have a look

I would wind it in and see how you go.

At least the car works well otherwise...I assume

**Alfa Patch** · 24-08-12, 19:51

The car is running pretty well. I have an air / fuel gauge which i am waiting to fit the sensor on so i can double check fuelling is reasonable.

I have now removed the 'controller' again as i need to use the car and am much happier with a consistently safe (albeit slightly slower) car rather than a ticking time bomb that i can't relax whilst driving.

Does EVERYONE see their boost dropping off at higher rpm? Is this simply a case of the turbo being too small to maintain the pressure?

I guess that a manual bleed style controller will always suffer with drop off as the ammount of air to be bled at different rpm's would change? Is this something that electronic controllers eliminate using solenoids?

I have zero experience of turbo cars so am probably asking a lot of schoolboy questions

Patch

**AlfaJack** · 24-08-12, 21:57

I do find that the boost on mine will hit about 1.2 and then trail off to about 0.9.
So damn hard to test around here as you end up going pretty quick once you keep your foot down!

**Steve Webb** · 25-08-12, 07:26

Yep thats about the same as mine, the overboost function (Pierburg valve) is only designed and programmed to allow over the 0.7 base boost for a short time before closing.

**AlfaJack** · 25-08-12, 09:09

However with an MBC that Patch and I have it should maintain a contant pressure.

**Alfa Patch** · 25-08-12, 10:05

Constant boost pressure makes such a difference to the way the car drives. Even with lower boost the more linear power makes it much more confidence inspiring and easier to push to the limit.

Can actuators be changed for ones which allow higher boost? I'm not convinced by these bleed controllers, they do seem to adversely affect high rpm performance.

Does anyone get constant boost? If so how? Unless the turbo is not able to pump enough air at high engine rpm to maintain the boost level surely its possible.

**Alfa Patch** · 25-08-12, 10:11

With regards to testing I certainly know what you mean. My boost gauge is where the stereo was so I have to drive with my foot flat to the floor whilst staring at the passenger footwell!! It's incredibly unnerving.

I have found that 5th motorway driving is the best way to get an accurate idea of what boost levels are but needs to be done at night as speeds are so high. My drivers windscreen wiper decided it couldn't deal with the wind speed at 135 mph last night and left me blind for the drive home. I'm not sure if the police will accept "trying to get an accurate boost pressure reading" as a valid reason for such speeds but it would be the truth.

**Steve Webb** · 25-08-12, 10:53

Originally Posted by Alfa Patch

I have found that 5th motorway driving is the best way to get an accurate idea of what boost levels are but needs to be done at night as speeds are so high. My drivers windscreen wiper decided it couldn't deal with the wind speed at 135 mph last night and left me blind for the drive home. I'm not sure if the police will accept "trying to get an accurate boost pressure reading" as a valid reason for such speeds but it would be the truth.

On a private test track of course.

**Alfa Patch** · 25-08-12, 11:20

Originally Posted by Steve Webb

On a private test track of course.

Of course

The A3 is private right? I don't actually advocate such speeds generally but sometimes a mans gotta do what a mans gotta do.

This is interesting:

http://miataturbo.wikidot.com/boost-control

Any thoughts? Probably worth trying.

**AlfaJack** · 26-08-12, 23:15

I'm going to try it too....unless anyone can suggest a reason not to?

**the wombat** · 27-08-12, 17:35

Interested to hear the result. Makes a lot of sense. Very interesting thread.

Mine is running the standard pieburg valve with a hybrid turbo and I am seeing the same tail off in boost.

**AlfaJack** · 27-08-12, 19:31

The evitable question - for what reason is it not like this from factory? Probably safer for longevity of the engine.

**Alfa Patch** · 27-08-12, 21:02

Couple of updates.

Firstly i got bored of standard boost and thought i'd have a go with the 'controller' again.

I decided that it must be boosting too much due to too higher pressure on the ball from the spring but i couldn't release any of this pressure as it was wound out as far as it could go.

I considered shortening the spring but didn't want the edge getting trapped on anything so i destroyed a load of perfectly good ballpoint pens instead....

In the picture you can see the controllers spring on the left and 3 others from the pens moving towards the right. I opted for the one on the far right as it was the shortest and had a sort of trumpet to sit the ball bearing in. This particular spring is from a parker ballpoint if anyone else ever has similar problems.

With the new spring in the controller and the controller itself back in i went for a cautious drive. Hurrah i was seeing about 0.7 bar of boost!!!!

I am slowly winding the boost up but am experiencing boost drop off at rpm as everyone else seems to as well.....

**Alfa Patch** · 27-08-12, 21:16

Secondly i thought I'd have a go at copying the MX5 thread i posted on here.

I removed the hose going to the idle control valve and connected in a barbed connector from a kart fuel tank. (Pic 1 + 2)

Then i blanked the original turbine 'actuator outlet' and spun the boost controller round so i could connect it to its new feed. (Pic 3)

I went for another run and somewhat disappointingly still experienced boost drop as rpm rose.

Now i appreciate that this is hardly a fair test, i know my car has various small boost leaks and the way that i connected the new 'actuator outlet' was probably leaking a bit too but i had still expected better results.

Really someone needs to take the plunge and do it properly, preferably someone who has a solid base car. Mine still has too many unknowns to prove or disprove this.

Whats still bothering me is that we have people on here with monster engines (300+bhp), surely they aren't running around with boost drop? How are they getting around it? It's such a simple principle that the answer can't be too complicated......can it?

**SteveNZ** · 28-08-12, 01:03

There are many cars with the boost reference taken after the intercooler as standard. T

This is only really necessary when the intercooler is a restriction. Most intercoolers are designed not be restrictive over their intended use. However when we operate them outside their intended use (more boost/RPM) it may create a larger pressure drop which will cause boost to drop. The question then is should I really be upgradng the intercooler rather than boosting higher to overcome the restriction.

This problem is nothing new, people with 300hp do experence boost drop off. You can spend a lot of money of electronic boost controllers, manifolds and wastegates to get this right. I know it is bloody anoying but that is how it is.

The problem is the mechanical limitations of the wastegate and the efficiency of the turbo. If you get that sorted you wont have a problem. It is very difficult for the internal wastegate to accurately control the boost if the turbo is operated in an inefficient zone. An external wastegate will usually solve the problem.

Likewise, a larger or more efficient turbo for your application will be easier to control with a basic internal wastegate.

**AlfaJack** · 28-08-12, 08:26

JimN's car was running an eBay Chinese turbo with a new IC and he could maintain about 1.45 boost on the track all day long. Was very impressive.

**Evodelta** · 29-08-12, 20:52

Originally Posted by SteveNZ

There will be a small port drilled in it somewhere to bleed off some air. It would not raise the boost if it wasn't, it's just physically impossible.

I've have many manual boost controlers, with and without the ball and spring, over the years. They all have the small bleed somewhere and they all work even if you remove the ball and spring. The ball and spring is not there to control the boost pressure, it's there to reduce wastegate creep, make the boost come on faster. It's still the bleed function that actually raises the boost.

Electronic boost controlers are exactly the same too, they are essentially a bleed valve that is just electronically controlled. Like I said before, any air bled off is totally insignificant. With the right restrictor, the volume of air we are talking about is miniscule.

There are a lot of myths floated about to make one product sound better than another. Don't get sucked in.

I know about the myths, I read the internet and your posts - like the one where you thought that a Coupe runs 12psi of boost (it's 15) and that you'd gained power by replacing the 15psi chip with another 15psi chip.

Not all B & S valves have holes in them, if they do you can block it off and it doesn't make any difference to the boost pressure, I know because I've done it.
They definitely do not bleed off boost.
A full explanation here: http://autospeed.com/cms/title_Thirt...7/article.html

**SteveNZ** · 30-08-12, 05:44

That article clearly states it needs a small hole in the valve body they call an "excess pressure valve". Call it what you like, that hole is bleeding off air (the excess pressure) as soon as the ball moves off the seat. Can you not see that?

Sure, without that bleed the boost will still increase untill the ball moves off the seat, opening the WG at that point. However in that state, the chamber will eventually fill with boosted air until the pressure has equilised on both sides of the ball and seat. That "excess pressure vale" needs to start removing that pressure or the wastegate will continue to open further. Without that bleed the valve is not controling anything.

Afterall the only way to accurately hold the WG in a desired position (i.e. to control boost) is to REGULATE the pressure to it. A ball and spring only can't do that, it can only turn it on or off.

I agree this is different to a "gated" boost controller that uses the ball and spring just as a gate. i.e. its is not adjustable. These need an adjustable bleed hole to set the desired boost pressure. The principle is still the same.

**Evodelta** · 30-08-12, 10:57

Ok, lets talk about one thing at a time, forget the rest:

Originally Posted by SteveNZ

That article clearly states it needs a small hole in the valve body they call an "excess pressure valve". Call it what you like, that hole is bleeding off air (the excess pressure) as soon as the ball moves off the seat. Can you not see that?

No it isn't. It clearly states:

A small hole in the valve body (called an "excess pressure valve") allows pressurised air to escape from between the controller and wastegate actuator following a boost event. This pressurised air would otherwise be trapped against the wastegate actuator and cause poor boost response.

It is NOT using that hole to control the boost.

I'll type it out again because you must think I'm lying or something:

I put plasticine over this little hole and went for a drive, it did not effect the boost pressure.

There wasn't enough pressure to even blow the plasticine out of the hole or off the valve yet the car is running at 1.5 bar.

If it was using this hole to control the boost how did that happen?

**wrinx** · 31-08-12, 07:32

Isn't boost drop off perfectly normal...caused by the exhaust output dropping off as the engine's speed plateaus and can't maintain the required output...or am I simplifying things too much?

wrinx

Edit: just read the Miata article so the above is redundant

**SteveNZ** · 31-08-12, 12:30

Originally Posted by Evodelta

Ok, lets talk about one thing at a time, forget the rest:

No it isn't. It clearly states:

A small hole in the valve body (called an "excess pressure valve") allows pressurised air to escape from between the controller and wastegate actuator following a boost event. This pressurised air would otherwise be trapped against the wastegate actuator and cause poor boost response.

It is NOT using that hole to control the boost.

I'll type it out again because you must think I'm lying or something:

I put plasticine over this little hole and went for a drive, it did not effect the boost pressure.

There wasn't enough pressure to even blow the plasticine out of the hole or off the valve yet the car is running at 1.5 bar.

If it was using this hole to control the boost how did that happen?

I don’t know mate, a leak? Or maybe the same reason why you didn't also suffer "poor boost response" which they say will happen if you don't have the hole. And there leys the whole point IMO, poor boost response.

Evodelta, I'm not here to argue, if you want to believe what's written in that article as gospel, go ahead. For anyone else that is willing to look at it from first principles, rather than an autospeed salesman, it's obvious how it really works. This is what I know; take what you want from it.

These so called boost controllers are not an innovative new technology or anything. They are nothing more than very crude air pressure regulators. A pressure regulator in its most simple form is just a variable restrictor that is controlled by a set load (spring).

http://en.wikipedia.org/wiki/Pressure_regulator

As I have said earlier if you add a restrictor in front of a bleed valve, less air will need to be bled off. Make the restrictor very restrictive and the air bled from the system can be so low, it is negligible. It is also possible to adjust the boost pressure by adjusting the restrictor, not the bleed. These boost controllers work exactly like this with only one difference, as the restrictor is variable (it's a pressure regulator), it has the ability to be totally closed too.

You can use a pressure regulator (without a bleed) as a boost controller if you like. I have used commercial types (Festo) and they work well in some situations, e.g. to regulate the pressure to the top chamber on an external wastegate.

Pressure regulators on their own are not however very suitable as traditional boost controllers as they are intended to be used where air is continuously flowing through them. They "add" only enough air to match any loads (actuators etc) that use the air. As soon as the air flow stops (full chamber), they shut and then cannot regulate the pressure anymore. Whatever pressure remains will be there forever. Now that’s fine at that point where you reach desired boost but the valve then closes and becomes irrelevant and is doing nothing. That’s not really ideal. This is why they should incorporate a small bleed also. The small bleed (load) will enable air to flow through the system and let the pressure regulator work as intended, maintaining the pressure in the chamber. And under this regime, they are working like a traditional restrictor and bleed, only the restrictor is variable.

Using a pressure regulator as a boost controller may seem like a good idea but I don't believe it is. All engines have different dynamics so the effect will different but a set pressure to the wastegate may not necessarily give better boost control. A system that allows for variable pressure is of course going to be best.

**Alfa Patch** · 31-08-12, 12:49

It seems odd to me that boost drop off is accepted as 'just one of those things'. Surely bhp figures would be seriously improved by maintaining maximum boost up until redline? This has gotta be one of the first things you would sort on a turbo engine? Why bother even raising the boost if you don't already have what you should be getting at all rpm, are you not just stressing the engine at parts of its rev range where its never going to make max bhp anyway due to rpm being a big factor in the equation for bhp (i forget the exact equation)?

Is basically the only way around this to get a proper electronic controller? I am assuming that as they work with an electric solenoid they change the ammount of air they are bleeding off to maintain steady boost pressure at the inlet manifold regardless of rpm. If they work in the same way as an MBC and just bleed off a constant ammount of pressure they seem like a horrendous waste of money.

Steve - What you say regarding wastegates is interesting, i have read another post of yours where you describe the benefits of external ones and i am intrigued by it. Is the problem with internal that they are generally weaker? I guess that they are really only there to stop the turbo overboosting rather than maintain good boost levels. With this in mind I will seriously consider an external 'gate when it comes time to replace the manifold.

Patch

**SteveNZ** · 31-08-12, 15:31

Originally Posted by Alfa Patch

It seems odd to me that boost drop off is accepted as 'just one of those things'. Surely bhp figures would be seriously improved by maintaining maximum boost up until redline? This has gotta be one of the first things you would sort on a turbo engine? Why bother even raising the boost if you don't already have what you should be getting at all rpm, are you not just stressing the engine at parts of its rev range where its never going to make max bhp anyway due to rpm being a big factor in the equation for bhp (i forget the exact equation)?

Is basically the only way around this to get a proper electronic controller? I am assuming that as they work with an electric solenoid they change the ammount of air they are bleeding off to maintain steady boost pressure at the inlet manifold regardless of rpm. If they work in the same way as an MBC and just bleed off a constant ammount of pressure they seem like a horrendous waste of money.

Steve - What you say regarding wastegates is interesting, i have read another post of yours where you describe the benefits of external ones and i am intrigued by it. Is the problem with internal that they are generally weaker? I guess that they are really only there to stop the turbo overboosting rather than maintain good boost levels. With this in mind I will seriously consider an external 'gate when it comes time to replace the manifold.

Patch

I agree with your first paragraph, stopping boost dropping off is very important if you are looking for maximum performance.

To give the engineers some credit most cars from the factory hold relatively stable boost. And where they don't, if you didn't have a boost gauge you probably would not notice. Maximum boost at redline for max power is not usually the most important factor for a road car. They are usually tuned with smaller than optimum turbos for obvious reasons.

Usually it's only when we modify, operate them outside of their intended window where we usually see this problem at its worst. And that there is most of the problem. Fit a larger turbo suitable for boost and flow at higher rpm and a basic internal wastegate will probably do the job fine. Likewise fit a really good wastegate and problems are usually solved. Internal wastegates really only have limited effect. They are OK at working over a small window. External wastegates are far more precise and are able to work over a much larger window.

All my European cars have tended to drop boost at higher RPM but it is also common for the boost to rise unwanted. Japanese cars were bad for this, Subarus and Mazdas I recall would hit the boost cut with some minor modifications.

I have tried electronic boost controllers on cars where boost is falling off and they can’t always solve this problem. Some more expensive, highly tuneable controllers possibly could. But the run of the mill ones can’t. Even though they work on a closed loop, the trimming available is not fine tuned for your engine. The trim given may not be enough. They will be conservatively programmed this way to avoid wild fluctuations on other cars that don’t need so much trimming. I know on my car, as the boost dropped off the controller would have a go and bringing it back up, but it was too slow to be effective before I needed to change gear and boost control was “wavy”. Some controllers say they can self tune. I’m yet to see that work effectively. Fitting an aftermarket wastegate however usually has a dramatic effect. Any reduction in boost will move the wastegate and as these wastegates are designed well, should change the flow through the wastegate. The problem with an internal wastegate is a small movement in the gate may have little effect.

Internal wastegates are pretty crude. They don’t flow well. They operate like a swing door, not like a valve. Their flow rate vs opening is not going to be a nice shape so accurately controlling flow with that sort of valve is difficult to start with. And to control the valve, we usually get a small diaphragm with a week spring, mounted on a flimsy bracket. An external wastegate attends to all these problems. Flow well, large powerful diaphragm etc. Also if you want to use a boost controller with one, you don’t need to significantly change the pressure to the diaphragm. The underside just gets a boost line to open the valve, like a normal actuator. The valve will not creep so it does not need to be interrupted with ball and spring valves or manipulated with bleed valves to raise the boost. To raise the boost, you need only add a few psi of pressure to the other side of the diaphragm, effectively increasing the spring pressure. More boost is then required to open the valve.