i have just put on my new dump valves , had a job removing the recirc valves but got them off. just give it a run seems ok ..

but....... i was under the impression that every time i took my foot off the throttle even under normal driving it should hissss.

i have to cane it to get them to hisssss.

 

i think i may have to adjust them to hold the boost longer

or have i done all that work for nothing

 

apparently they have trumpets on the dump valves so there noisy ...but not yet

 

any advice on how mush i need to adjust them

thanks

What valves are they, and are they adjustable?

 

They wont sound if your driving normally as the car is running in vacuum they will only sound when you are genarating boost hence why they work when you boot it.

They will ONLY hiss if the turbos are making boost before you let off the throttle...

just adjusted the pressure. took the vacuum pipe of on tick over and its sucking. if i put my finger inside the valve and ry to lift the piston it mes easy but switch it off and i cant move it

i reall thought that having dump valves it would hiss everyime i accelerate

but its not now im pi44ed off....

if i put more pressure to the valve spring will that work

 

 

aaarrrrrrrrrrrrrrrrrrrggggggggggggggggggg doin mi edin

firstly, it shouldn't make much of a difference how much pressure you put onto the spring, if the pipe is under vacuum, the valve shouldn't lift! the valve will only lift whenever there is a positive pressure applied to the disc.

 

Secondly, why would you want to fit dump valves???? like many other threads have said on here.....they only decrease your performance......unless your running 600bhp+!!

 

But i suppose, everyone to their own opinion and all that!

When you step off the throttle, the turbo is still spinning and is forced to stop very quickly, due to that the air has no where to go. When you then step on the throttle, the turbo has to rev up again. This takes time, and the car feels tired.

When you close the throttle, a vacuum is built up after the throttle. A hose goes from the inlet to the dump valve, and the built up vacuum sucks up the plenum valve inside the dump valve, and releases the over pressure built up before the throttle. The air goes out into the engine compartment and creates a the sound you hear from turbo. When you then start to accelerate, the vacuum disappears, and the dump valve closes, and the turbo pressure is on top at once. The car feels a lot more powerful than before. This is why you will not hear the vavlves at low revs. You need to have the turbo's creating enough boost to have the excess pressure to blow out of the turbo's. The only way you will get the valves to work sooner is to have your turbo's kick in sooner i.e lower revs.

The recirculation valves do exactly the same thing -they are fitted as standard but dump the air into the inlet rather than to atmosphere. This means the air the ECU has measured into the engine by the MAS stays in the system, rather than causing overfueling when you step back on the throttle.....

Recircs are better:

Boost valves eliminate compressor surge but we did confuse the engine just a bit since the ECU already told the injectors to issue fuel to be used for the air that we've now thrown out. Other than that sounds like a good idea right? so what if were running a bit rich for a moment, no big deal. Before you place your order read on...

 

The Re-circulating Valve... a better idea:

 

How about instead of poking a hole in the turbo to intake manifold tube and just letting the air leak out wherever it wants to, we could direct that pressurized air somewhere else where we could hold on to it until we need it again? The intake side of the compressor housing (between the intercooler and the turbo) would be a good place wouldn't it? that way we wouldn't slow the turbine down and we would have that pressurized air that would have otherwise been thrown out, ready in a really good place when we need it. On top of that eve got still got the correct air/fuel ratio going since we're not throwing and air out, just moving it from one place to another within the intake system. Instead of having to suck in air for the turbo to pressurize, we've got some pressurized air with the correct fuel amount already waiting. Now we've got all the benefits of a blow off valve and then some. That's a re-circulating valve. Let's all order re-circulating valves then and skip the blow off valves completely. They're probably gonna cost a bit more than the blow off valves since they work a little better right? Now the big surprise... Re-circulating valves were engineered into the design of your 90+ twin turbo z on the drawing board... you've already got them...

 

In conclusion: You could always disconnect your stock re-circulating valves (which you have to do to install blow off valves) and spend 500-600 bucks for blow off valves and what will you get? better performance? No,

There's basic flaws in the physics behind his arguement tho ;)

 

If he's even trying to suggest the pressure from the recirc will boost the compressor then he's wrong. Any excess pressure dumped will take the easiest route out, and thats back out of the air filter... Goose honk anyone?

suppose it a personal preference thing..... Dump vavles don't really add any performance value unless your running very high BHP. Suppose it's more a crowd pleaser and grin value more than anything....

 

Fast and Furious...lol.... more furious at the price paid to power gained

it is a bit of a crowd pleaser realy.

i guess ill strip it all down and put the recircs back on...

 

for sale .....dump valves ..one owner low milage...

what if i sealed up the recirc pipes now there off and move the dumps closer to the throttle body would that help ... always wanted a turbo car hat hissed ...got the car no hisssss

what if i sealed up the recirc pipes now there off and move the dumps closer to the throttle body would that help ... always wanted a turbo car hat hissed ...got the car no hisssss

 

should work mate. Moving it closer will give you a bit more pressure when the turbo dumps the excess boost as the distance travelled is shorter. Technically the idea works. Give it a go see if it works mate

There's basic flaws in the physics behind his arguement tho ;)

 

If he's even trying to suggest the pressure from the recirc will boost the compressor then he's wrong. Any excess pressure dumped will take the easiest route out, and thats back out of the air filter... Goose honk anyone?

Goose honk is caused by the reed valves in the recirc fluttering: http://www.aus300zx.com/forum/showthread.php?t=251871 and is typically caused / aggravated by induction kits. My stock TT hasn't honked once in 8 years.

 

There's no flaw in his physics. BOVs release system pressure into the outside which does stop compressor stall so the compressor is still going so the pressure on the input side is lower than it would be if the pressure released downstream to stop compressor stall was put back upstream which is what the recircs do.

 

That's one of the reasons Mr Nissan put them there.

 

The quote was taken from one of Twin Turbo net's faqs http://www.twinturbo.net/ttnetfaq/FAQpages/bov.html which has been up there for 6 or 7 years to my memory and they're pretty hot on technical accuracy.

The dumped air will find the find the path of least restricion - back out through the filter!!! Agreed there will be a VERY SLIGHT difference but it will be minimal to the point of almost imeasurabe.... His comments suggest it gives some massive performance gain, which it won't.... Main reason for recircs is that the ecu has already measured the air and is fueling for it

The dumped air will find the find the path of least restricion - back out through the filter!!! Agreed there will be a VERY SLIGHT difference but it will be minimal to the point of almost imeasurabe.... His comments suggest it gives some massive performance gain, which it won't.... Main reason for recircs is that the ecu has already measured the air and is fueling for it

so how about if the valves were to be moved closer to the air filter?????? :nelson:

ok ok you win

 

ill go back to recircs

 

thanks lads for your help

just a quick one wtf is Goose honk please? pardon my ignorance!

just a quick one wtf is Goose honk please? pardon my ignorance!

Goose honk is caused by the reed valves in the recirc fluttering: http://www.aus300zx.com/forum/showthread.php?t=251871 and is typically caused / aggravated by induction kits. My stock TT hasn't honked once in 8 years.

..

lol none of that means anything to me lol im mechanically inept ill just accept it exists as reed valves and Pod filters mean nothing to me lol

The dumped air will find the find the path of least restricion - back out through the filter!!! Agreed there will be a VERY SLIGHT difference but it will be minimal to the point of almost imeasurabe.... His comments suggest it gives some massive performance gain, which it won't.... Main reason for recircs is that the ecu has already measured the air and is fueling for it

He doesn't claim a massive performance gain. His comments are more that there won't be the lack of pressure cause by boost valves. Which is correct.

 

In any case there is a reasonable amount of inertia in the air already moving through the system which won't suddenly vanish and let through dumped air in the reverse direction.

 

If there are any measurements showing the difference is "almost immeasurable" I'd be interested to see them. By definition, the pressure lost is enough to make those bloody awful noises dump valves make.

 

And, what's worse, as any physicist or engineer knows, noise is a symptom of inefficiency in a process and who wants to make a Z more inefficient than it already is!

 

He does state the ECU reason. So recircs don't confuse the ECU or risk fubaring up the air/fuel mix which is a major cause of detonation.

As any physicist knows, pressure acts in all directions, so any inertia in the air through the intake will rapidly be defeated. Listen to most cars with an induction kit and stock recircs and you can hear the air rushing back out of the airfilter on lift off.

 

One thing worth noting with recircs is that the air being put back into the system has already been compressed and therefore heated by the turbos. Dump valves you get fresh, cold air every time so this would fight against detonation! Also, if the ecu is fueling for air that is no longer there, then this will cause a RICH condition, combatting detonation again...

 

The noise is caused by energy loss, would be interesting to see the energy loss through heat disipation from the intercoolers with the hotter air from the recircs ;)

As a physicist I certainly know that pressure acts in all directions. OK maybe for accuracy I should have said momentum instead of inertia but we were talking principles instead of quantifiable and measurable things. To take this case, Momentum = p = mv (mass x velocity) and we were comparing the momentum of the air already in the intake system to the momentum of the air coming out of the recirc valve. This would show whether they would be in balance or whether one would overcome the other.

 

First approximation is that the mass of the air in the system is probably significantly more than the mass of air introduced by the recirc valve. What's the velocity? Dunno but clearly quite a lot when under throttle. And non-zero when you lift off because recircs avoid compressor stall in the turbos. So somewhere between "some" and "quite a lot". That's for the system air. Now how about the recirc air. Gut feel that its velocity is quite high as it's coming from a compressed into a not-quite-so-compressed chamber. But maybe not as high in proportion as the difference in mass.

 

So for first approximation it appears likely p(system) is greater than p(recirc).

 

Second approximation don't forget the recirc air is coming into the chamber orthogonal to the flow of the system and hence since v (and hence p) are vectors, the resultant is very probably in the same direction as p(system) i.e. towards the turbo.

 

Still, as I said, would be interested to see real measurements (or even references) to test the hypotheses.

 

Point about fuelling refers to feedback loops and the potential confusion of the ECU. If the ECU is fuelling for air that isn't there that will indeed cause rich but then what happens when the effects of the rich running are detected by the other sensors feeding the ECU and it leans off the mixture too quickly by which time you are back on boost and fullthrottle? What is the feedback time of this control loop? No idea. But I can certainly understand why dump valves can confuse the ECU and to me that's not an optimum condition.

 

All noise is indeed caused by wasted energy (unless it's your ICE or horn). The energy losses caused by heat dissipation from the intercoolers should be considered as the same system as that from the recircs - it's not an either / or. The thermodynamics of the situation treat the "thing which does the combustion" i.e. the engine from intake to exhaust as a single "black box" (not "black body" - that's a different thing altogether which we can cover in a different class) with the temperature of its inputs (the fuel and the air), the energy released through the exothermic burning of the fuel, the temperature of its outputs: the exhaust gases and the general waste heat; plus the energy released as noise.