ModifiedA4

As everyone knows there are seemingly TWO methods of installing a BPV. But I think it depends on location in the intake system how you orient the valve...

I've done some research and it seems there are two methods for solving the turbo overboost condition....

It seems engine type A has the BPV "bypassing the turbo" i.e. connecting the turbo intake to pressurized side preventing the overboost condition, and therefore the BPV should be installed pressure open.

In engine B, its seems SAABs are plumbed this way, the BPV "bypasses the throttle body" and depends on the Vaccum developed in the intake manifold when the throttle body closes to open the BPV which relieves excess turbo boost...

So in summary it seems there are pressure open and vaccum open BPVs...

Each method seems to protect the turbo from different sides...type A protects by equalizing pressure on the intake turbine, and type B protects by equalizing pressure on the exhaust turbine...

...It obvious to everyone that at least the 1.8t falls into the type A category...

I'm thinking the engine may be plumbed for both...
<img src="https://www.audiworld.com/news/00/newa4/pics/A4000034.jpg">

It almost looks like from this picture that there is some plumbing coming from just after the throttle body to just before it...cant tell...That mess may also be crankcase venting plumbing for emissions control...

Any thoughts????

Clark@turbo5.com

You should install the valve with the SIDE in the high pres boost pipe. The bottom goes to the small vent tube up to the non pres intake pipe. The photo is correct.

Some 1.8ts mainly DBW's car came with the valve backwards. This was done to decrease noise. Air rushing over the valve's lip causes the gurgling sound. This is fine with a stock car as there is only 5-7 psi. Once chipped the valve will be blown open and it will leak. It will also have a hard time sealing back tight on a fast shift.

Every Turbo Porsche made has had the valve installed just like the photo.

The line by the TB is the Crank case vent line. It does not connect to the BPV system. It leads back to the PCV valve and then into the air stream after the MAF.

Some of us have disconected this system and used a Catch tank instead. This stops oil from entering the intake system.

Clark

Audiboy

Bypass valve is used to relieve pressure when the throttle body closes. Why - this would prevent devastating detonation of an overlean condition when the throttle is opened and all that build up pressure behind the throttle butterfly will suddenly rush into the cylinders without adequate timing retard and fuel compensation (Note you can eliminate the BPV if you are using your car for race purposes and can control your throttle in a manner different from everyday driving).

In fact, I must add that bypass valve is a blow off valve with the output of the valve recirculating into the intake of the turbo because the valve and turbo is after the meterered air of an air flow meter or mass air sensor setup. Cars that have the turbo/SC before the air meter or use a MAP sensor as primary input for mixture data during boost or vaccum, can use a blowoff valve (Such as GM's, Honda's, etc).
A blowoff valve or bypass valve is nothing more than a diaphram that opens when vacuum is applied to it - simple as that. Heck, an EGR valve can be used as a blowoff valve for that matter - well almost. You have to tune the spring such that when it opens at a certain pressure when there is no pressure on the diaprham side or vaccuum is applied, otherwise it may open right away.

Why would most bypass valves not act as a overboost protector? Well, you have manifolf pressure entering the diaphram via small hose pushing the diaphram shut plus the spring pushing it shut all competing with the pressure on output of the turbine which pushes a smaller area of the diaphram, compared to the pressure on the spring side exposed to the whole diapram.

You wanted a pressure pop off valve which are more like extinct in todays turbo applications, but if you really want one, here's a simple way. Get two valves, hooked up identically (parallel to each other), with one of the diaphram's vacuum line unconnected. Then tune the spring of the unconnected one such that it will give at high pressures. This will then open and vent back into the intake of the turbo relieving the spiked pressure until the wastegate catches up. The other BPV will act the same way as normal, opening when the throttle closes. For this, it is good to have the forged valved because you can open it up and play with spring tensions.

Lucas_Gchips

There is a vaccum control line from intake manifold (Around the cutaway) to the BPV valve, that is not shown altogether in that pic.

Ned Cejaj

You cannot route a second bpv and expect it to act as a pop off valve, i.e. release boost in case of a pressure spike.

a boost pressure spike will occur if the wastegate is stuck and allows the turbo to overspin. Now, what pressure would we set the pop off valve to go off at? 20psi? Ever notice the boost readings on your car? It will run, if chipped, 18-19psi, and then back off to around 12-14. If the wastegate were closed, and you ran 19psi of boost at 6000rpm, you *can* damage the engine easily before the pop off valve would even come close to releasing the pressure.

Thats why, the ECU modifies target and actual boost. when the difference between the two is greater than a set value, a fault code will trigger, and the ECU will cut back boost.

Ned

frank

Both Audi and Saab valves use a vacuum/Boost hose to Open/Shut the valves.

The spring is likely there to assist with keeping the valve closed at low boost/vacuum, it sure isn't neccesary to close valve.

The vacuum line is the key. but no matter which pipe has the boost entering the valve will open.

It will vent boost if the vacuum line is lost or cut. So you won't blow or stall the turbo.

But until you fix that hose I doubt it will hold any boost, as the stock spring will open around 8lbs without assistance from the hose.

Audiboy

do you even know how many cfms it takes at 6000 rpm and how much pressure can be produced by a K03 at that pressure?

Also, you said it yourself, if chipped 18-19 psi - what do you call that if you only have a 1 bar chip? imperfect programming? You have a 1 bar, therefore you want to cut off excess pressure slightly above that. You will detonate an engine easily in the low rpms, not in the high rpm range. Boost spikes happen in lower rpms when the turbo has adequate air flow to produce boost to match cfm requirements. A wastegate is very slow to react. You have to deal with the cracking pressure first much sooner than the final boost cutoff pressure. For example, if you want to limit the boost at 12psi, you may program the wastegate to start opening (cracking) at 8 psi such that the turbine overun will not exceed pressure.

BTW, I am only showing one way to create a boost spike pop off valve with an existing BPV. Does that mean that everyone should go out there and build one? Not unless they can tune it properly, no way. Do we see boost spikes - yes. Do we have anymeans to control it now, probably not.

Also, you probably won't blow up a the 1.8 motor at 19 psi @ 6000 rpm because chances are, for a turbo to sustain that boost, you probably run 24 psi or higher at the lower rpms, so the engine rpm will never get that high since you blown it down low unless of course you beefed up the internals

frank

until the wastegate does it's job.

no?

Audiboy

ping? It's a bad thing but it happens. Plus, retarding the timing cannot really compensate for an overlean condition. The mixture will reignite because of heat and pressure, no spark needed

Audiboy

good, hence a pop off valve