JimSchwartz

I'm not affiliated with any of these companies, blah, blah, but ever since I bought my wife a TT, I've been looking at the bypass valve issue rather closely.

I've certainly been amused by the intense bypass valve wars that continue to wage on the internet. I'm not going to comment on the quality of the valves currently out there, but there is one point that I feel I *have to* speak up about. I've been building turbo charged cars as a hobby for years, and I've always known about how the Bosch bypass valve really wasn't the best choice out there.

However, the construction of the Bosch valve is kind of clever, as it allows usage in either orientation. The rubber diaphragm has a shoulder that runs around it and overhangs a channel in the valve body. This shoulder is an exposed surface that can catch vented boost, even though the "face" of the diaphragm may be facing the low pressure side of the intake. The valve is technically opened when manifold vacuum is applied to the upper chamber, but it works best when the vented boost is working with the valve diaphragm, not against it or without it. As long as there is a surface on the diaphram to catch boost, the valve can also act as a overboost safety release, as it can be pushed open by boost alone that way.

Now here is a *BIG PROBLEM* that I have noticed - the Forge valve guys have it *ALL WRONG*. They keep talking about how the Forge valve can be oriented in the same position as the stock valve, and how that fact is a great benefit over the Bailey valve. Since the Forge valve is a piston type valve, and it doesn't have internally a shoulder or surface like the stock Bosch valve, it *must* be oriented with the face of the piston facing the high pressure side, which is opposite from stock. Failing to do so, the valve will not have the added benefit of the boost pushing it open when venting, and it can't work as an overboost safety release!

It also makes the whole spring stiffness option moot, since that only has any meaning if the boost is directly pushing against the piston face, which it isn't if you install it the way they suggest.

I guess my final point here is: the Bailey valve guys got it right, and "reversing" the valve opposite from the stock orientation is the proper way with a piston type valve. So much for all these great benefits the Forge guys keep bashing the Bailey guys over!

I certainly don't mean to **** on anyone's parade - feel free to flame away if you've got the facts to back it up!

Jim

PanTTher

It sure doesn't sound like it from your write up. The Forge design works just like the stock factory valve even though it is a piston type. It will open under excessive boost even without vacuum on it no matter which way it is oriented. And I have the “facts” to back it up buddy!

nifTTy

I have no facts to back up anything, but I do have a forge valve installed. It has "worked" perfectly for me from day 1. If the folks at Forge got it all wrong, I wish that Audi had gotten it wrong the same way to start with. I don't plan to change it. Pete, you must have some thoughts from Stratmosphere.

CarTTman

Thanks - I'll close out my short position on Bailey & buy some Forge puts ^^^^^

frank

There *IS* a shoulder on the forge valve, just as with the Bosch part and the Bailey. Go to the Stratmosphere website and look at the photo of the bottom of the piston.

If it didn't have it you would be correct, but most people seem to think the bosch doesn't have one either! =D

BTW what made you think that any of the piston valves had no shoulder?

CarTTman

D'oh! Any one want to buy some Forge puts (cheap!)

Pete @ Stratmosphere

rest now. The Forge works properly in the OEM configuration. -Pete<ul><li><a href="http://www.stratmosphere.com/forge_valves.htm">Stratmosphere Forge Diverter/Dump Valves for the 1.8T</a></li></ul>

Forge Motorsport UK

Obviously as the manufacturers we need to reply to these comments
Forge Motorsport have been manufacturing ,designing and developing Blow off valves for many years, we do this every day, all day and its not a hobby.

We have carried out tests on the Bosch valve ,the results are as follows.
In the tests we tried to vent the air through the exhaust port of the Bosch valve,At 30psi,the diaphragm did not move off its seat in any direction,this suggests that this would not act as any kind of overboost protection.

We have carried out many years of testing of blow off valves both for road and race applications to ascertain the best orientation of the valves.

In our opinion the diaphragm valves are by far the most efficient and responsive valves, but due to the nature of the diaphragm these are prone to failure without warning.
We have fitted the Bosch valve to a Ford Cosworth race car which is running a boost pressure of 32psi, the valve worked well fitted correctly, with boost sent up through from the bottom part towards the vacuum port,the valve had no running problems until the diaphragm failed,

We then fitted another Bosch valve as on the TT with the boost via the exhaust port (side of valve).
This caused excessive compressor wheel stall and violent air turbulence around the wastegate valve.
This will cause the following effects to the turbo. Excessive turbo bearing wear , which could cause the blades to fracture and fragment into the engine.

We have also seen in extreme cases the compressor wheel snap.
We would never suggest that any of our valves are fitted backwards to the aforementioned reasons.

The Bosch valves are fitted to many European turbo cars as OEM that we also our valves for aftermarket replacements.

Thanks to Jim for his moot points.

Forge Motorsport UK

Obviously as the manufacturers we need to reply to these comments
Forge Motorsport have been manufacturing ,designing and developing Blow off valves for many years, we do this every day, all day and its not a hobby.

We have carried out tests on the Bosch valve ,the results are as follows.
In the tests we tried to vent the air through the exhaust port of the Bosch valve,At 30psi,the diaphragm did not move off its seat in any direction,this suggests that this would not act as any kind of overboost protection.

We have carried out many years of testing of blow off valves both for road and race applications to ascertain the best orientation of the valves.

In our opinion the diaphragm valves are by far the most efficient and responsive valves, but due to the nature of the diaphragm these are prone to failure without warning.
We have fitted the Bosch valve to a Ford Cosworth race car which is running a boost pressure of 32psi, the valve worked well fitted correctly, with boost sent up through from the bottom part towards the vacuum port,the valve had no running problems until the diaphragm failed,

We then fitted another Bosch valve as on the TT with the boost via the exhaust port (side of valve).
This caused excessive compressor wheel stall and violent air turbulence around the wastegate valve.
This will cause the following effects to the turbo. Excessive turbo bearing wear , which could cause the blades to fracture and fragment into the engine.

We have also seen in extreme cases the compressor wheel snap.
We would never suggest that any of our valves are fitted backwards to the aforementioned reasons.

The Bosch valves are fitted to many European turbo cars as OEM that we also our valves for aftermarket replacements.

Thanks to Jim for his moot points.

Jenner

In your post you say:
"We would never suggest that any of our valves are fitted backwards to the aforementioned reasons."

Pete in his post says:
"The Forge works properly in the OEM configuration."

To me the OEM configuration is the BACKWARDS configuration. Pete says it works in this config and you say it doesn't?

I'm not trying to cause any problems, just looking for an answer/clairifaction. Thanks!