Vaccum query

[A80Avant]

i was wondering, when casually driving around and the car is under vaccum(as shown from our boost gauge), what is the recirc valve actually doing?

Is the vacuum supposed to be the same under both sides of the valve (small tube and the inlet manifold tube) so as the piston is basically shut?

If that is the case,what is the role of the stregth of the spring?Is it there basically so as to open the piston slower or faster when the TPS goes from the open to closed condition,and relieve the backflowing air?

If that is the case, a softer spring, would actually be better than a stiff spring for the valve operation,because it would open the valve faster to relieve the pressure. WHy is it that we find stiffer springs to work more crisp and faster with the valves then?

reason i ask is the fact that i noticed that the 006 to the hybrid forge valve i tried,have as a main difference(other than where the air is dumped) the spring strength. The feedback i go from the car was that during cruising and when boost needs to be built, it starts up a bit slower than when i used the 006 valve.

[s2_bo]

Under vacuum the oem valve is actually open, as the vac line sucks the diaphragm up and therefore opens the seal. The spring is not strong enough to keep it shut

This is why if you use a oem bosch valve and vent it to atmosphere whilst still having the maf on the vacuum side you will get very bad idle.

A stiffer spring holds the valve closed so it doesn't open under vacuum, which it doesn't need to anyway....

I found that an oem bosch valve stayed open until the boostgauge read +0.2bar. This is also why a stiffer spring or better valve would illuminate boost leak under vacuum. Not really a problem as it leaks back to after the maf anyway so the air is already accounted for but it goes though the turbo again etc. etc..

[A80Avant]

The functions of a blow off valve

Without a blow off valve, when you let off of the gas, the compressed air in your intake piping increases to great pressures as the turbines in the turbocharger are forced to a screeching hault. The extreme pressure forces the air back through the turbocharger, increasing the wear on the turbo.

With a blow off valve, when you let off of the gas the air pressure left in your intake piping is relieved as the blow off valve opens up. This allows your turbo to continue spinning in the proper direction, preventing damage to the turbo and allowing for a faster return to positive air pressure in the intake piping.

How it works

A small diameter hose runs from the intake manifold to the blow off valve. When the pressure in the intake manifold is positive (in boost), the pressure in the small hose keeps the wastegate closed.

Once you let off of the gas, the throttle plate closes, and all of the air in the intake manifold is sucked into the engine. With negative, or zero pressure in the intake manifold, the blow off valve opens up and releases all of the compressed air from the intake piping.
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something i found online...This just enhances my question as to why we are not going for softer springs rather than stiffer?

Stiffer spring would mean that im actually doing more harm potentially to the turbo by allowing more pressure to build up before the valve opens up. A softer spring would open up faster and get rid of all the compressed air,thus keeping the turbo safer.

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@ s2bo: would an open valve under vaccum could explain a slower reaction that im having then?

[s2_bo]

Softer spring will leak air, stiffer will not.

No need to open faster as the pressure in the intake piping will easily force its way out as soon as the TB is closed.
If the pressure is little i.e. 0.5bar or less then the compressor stall will be next to none anyway so it doesn't matter that the pressure release valve doesn't open as quickly.

This is why a valve with an adjustable spring is good as you can tailor it to your car and to your requirements.

[A80Avant]

ok that clears things quite a bit then.

im expecting to have the stiffer spring configuration on the forge hybrid valve next week to try it out.

im going to post some photos shortly of the valve itself dismantled

[A80Avant]

Here is the valve










smaller outlet for the atmosphere function,but it can still be changed to the larger one

[s2_bo]

Looks similar to the turbosmart internals, how much was it?

[A80Avant]

140GBP+shipping if i remember correctly.

intersting thing is that if i turn the spring all the way, the atmospheric function is deminished simply because the piston wont go all the way far up to open the small opening of the atmospheric side.SO it seems to act only as a recirc valve in that situation.

[A80Avant]

tested today the version of the spring that john sent me and the results are much better.It now has no difference from the 006 forge i use and it does make a nice sound like the SQ!!! me likes!!!

[Bram]

Do you have a picture how and where you connected this DV?

[s2_bo]

Same place as the oem DV. Just one side venting to atmosphere.

[Acidburn]

Got any sound clips vasilis?

[A80Avant]

excactly.Only difference from forge manual is that you connect the pressure side the opposite way as apposed to the recirc valve. Hence the small vaccum hose and the piston of the valve is in line with the pressure side.

[A80Avant]

there it is explained!

[A80Avant]

No sound clips yet.I just managed to test it once today. but i will try to make some!