Bov Reverse Vented

[IH8TOADS]

After refitting my BOV (kompact turbosmart) last night the little cogs in my brain started turning again. The standard Bosch valve is fitted in reverse, which means boost enters from the side of the valve and exerts pressure aginst the side of the piston instead of against the bottom of the piston as in a conventional valve. This got me thinking as to why bosch would do this?? Anyway I ended up with two assumptions/question.

1) The Bosch valve accepting boost from the side would actually not leak in raised boost applications despite being plastic?? Some people have assumed that the bosch valve would leak if the boost was raised (say over 11psi). However I cant see how this would happen on this valve.

2) You could potentially reverse the fitment of the valve so that boost is directed against the bottom of the piston (and plug the return whole in the cast aluminium intake) so the valve would vent to the atmosphere as in a conventional valve (well boost could still enter from the side and produce atmosphere venting noises if the intake pipe was pluged.

Anyways what are people thoughts on this and has it ever crossed anyones mind that the standard bosch BOV is fitted in reverse.

[Lawsy]

Interesting points mate... To be honest, I'm not sure. All I know is that if you can somehow use the discharged pressure to help build boost more quickly in the next WOT application, then your onto a good thing..

[F6_Tornado]

The valve is fitted exactly as it should and works very simply despite many thinking it is wrong.

The side port is to the Boost side and the top port is to the intake side.

The internal piston/valve is spring applied and Boost/vacuum controlled/assisted.

So when in closed loop (idle) the intake manifold has a vacuum and as such this Vacuum acts to draw the piston/valve backwards allowing air to travel from the air filter direct to the throttle body allowing the engine to run as a N/A would.

When you open loop or apply the throttle the vacuum diminishes and becomes a positive pressure so the piston/valve in the Bov closes so no air can travel from the air filter direct to the throttle body and as such must all flow through the turbo.

As the turbo boost increases so does the boost pressure at the back of the Bov and that boost with the spring hold the Piston/valve closed to ensure no loss of boost from the Bov. The higher the boost pressure the more force on the Valve so the chances of it leaking are minimal.

When you back off the throttle, closed loop, you will instantly have a vacuum in the inlet manifold which will pull the Bov piston/valve backwards which will intern allow excess Boost to flow back into air filter side.

Simple and very effective and having it return back into the inlet side make it a bit quieter than the aftermarket ones.

I suppose the only real advantage of the aftermarket ones is the fact that regardless of throttle position all air must travel past the turbo and at no time can the engine run an N/A situation.. Possibly advantageous with maybe less lag????

[F6_Tornado]

Also you will notice that the piston/valve has a small shoulder on it when looking down the side port (boost side). Boost acts on this small shoulder (force/area) but is not enough to force the Valve open until we have a vacuum which overrides the spring tension allowing the Bov piston/valve to open and dump boost back into the air filter side.

With WOT the boost pressure on this shoulder will be equal to the boost pressure acting on the back of the piston/valve in the Bov, this and the added spring tension ensures that the piston/valve will stay closed and as such there should be no loss of boost.

Then at Idle the vacuum overrides the spring tension drawing the valve backwards (at this time the shoulder is irrelevant) and as such ports the air filter side air directly to the throttle body making the system N/A (naturally aspirated)

[Lawsy]

Well at idle and at cruising speeds, this system would be far more efficient than drawing all the air through the turbine...

If you have to suck air through a few meters of piping and then through the fins of a turbine spinning slower than the air flow itself, then the the result is going to be an engine struggling for air. Surely this isn't more efficient than having the car run as an NA?

[F6_Tornado]

  IH8PORK said:

2) You could potentially reverse the fitment of the valve so that boost is directed against the bottom of the piston (and plug the return whole in the cast aluminium intake) so the valve would vent to the atmosphere as in a conventional valve (well boost could still enter from the side and produce atmosphere venting noises if the intake pipe was pluged.

<{POST_SNAPBACK}>

Trouble with that theory is what happens when you back off and have a vacuum?

The intake to the throttle body would be vented to atmosphere and then unfiltered air!!!

The only way to achieve this is to have a one way check valve fitted to atmosphere.

So no way to use the original BOV in that manner.

  IH8PORK said:

Anyways what are people thoughts on this and has it ever crossed anyones mind that the standard bosch BOV is fitted in reverse.

<{POST_SNAPBACK}>

Not sure exactly what you mean here!!!!

Are you saying the STD valve is fitted wrong way around??????????????

  Lawsy said:

Well at idle and at cruising speeds, this system would be far more efficient than drawing all the air through the turbine...

If you have to suck air through a few meters of piping and then through the fins of a turbine spinning slower than the air flow itself, then the the result is going to be an engine struggling for air. Surely this isn't more efficient than having the car run as an NA?

<{POST_SNAPBACK}>

Lawsy I think the idea is for better low down response as all the air must pass the compressor wheel and possibly keep the turbo spooling a tad (generally forcing the flow to pass though the charge side generating air movement whereas when through the BOV at Idle there is no air movement through the charge side) and as such maybe a better response with initial WOT and during gear changes??

Personally I don’t think there is a lot in it and definitely nothing in it at full noise so it won’t give you anymore outright HP but maybe less lag?

I’m sure some will have different ideas on this one.

One thing for sure is it’s a LOT louder!!!

[IH8TOADS]

F6, you are 100% correct in every way. Im not suggesting that the fitment is incorrect because it simply isnt and it actually is a very sound design. I see what you mean with with plugging up the cast intake pipe - it would be sucking unfiltered air at idle!!!!. I do understand how the Bosch system works, but with this design I cant understand how there could be a possible boost leak when psi is raised (as some people on this forum have stated) beyoud say 11?? The piston is snug as and therefore while "on boost" there is no vacuum and therefore the valve simply cannot open. Therefore no leak. I would think there would have to be rediculous boost pressures before the bosch valve would leak. So I would conclude by saying that a standard valve is capable of any edit upgrade.....or am I wrong???!!!!!!! cheers.

[F6_Tornado]

  IH8PORK said:

The piston is snug as and therefore while "on boost" there is no vacuum and therefore the valve simply cannot open. Therefore no leak. I would think there would have to be rediculous boost pressures before the bosch valve would leak. So I would conclude by saying that a standard valve is capable of any edit upgrade.....or am I wrong???!!!!!!!  cheers.

<{POST_SNAPBACK}>

Remember the boost is also acting on the back of the piston/valve !!

The thing is the vacuum is replace with boost so no matter how high the boost is it is acting on the shoulder of the piston/valve the same boost is acting in conjunction with the spring and will therefore not allow it to open no matter how high the boost gets @ WOT.

Spring tension plus boost holds it closed and it’s only when you have pressure differential between the charge side and the inlet manifold that is great enough to compensate for the spring value + boost that it will open.

For instance if the boost was UP and the throttle was partially shut off (not 100%) you may well have a situation whereas you have say 10psi in the charge side before the throttle body but a slightly lesser pressure in the inlet manifold say for instance 7psi.

This would then mean you have 10 psi acting on the piston shoulder but only 7 psi "and" spring tension acting on the back of the piston trying to keep it closed which would then allow for metering of the charge boost.

Simple but effective in theory no matter how high the boost gets the valve will not leak until such time that there is a pressure differential which will only occur when the throttle closes off to some degree to create an imbalance of boost between the charge side and the actual intake manifold. (either side of the throttle body).

[ROLMDL]

Just wanted to know what would happen if I was to remove the BOV

and block up the holes would there be problems or car might run crap???

[ROLMDL]

And if I wanted to still use the BOV but vent it out does that mean I would only have to block up the top outlet of the manfoild? and that it?