**RB2530**

How are you testing the WG? If you are doing a static test (ie car not running and just putting air pressure into actuator) the results won't mean anything. The reason is that when the engine is running there is also some exhaust gas pressure on the WG flap that is helping it to push it open...So its opened by a combination of actuator pressure and exhaust gas pushing on it. From what you are describing the problem may be that the WG flapper is not opening as much as it should. This could be because it is fouling on something in the dump or the linkage is binding or jamming which is stopping the WG from opening as much as it should.

Has your mate driven since the incident? If he has, then it's quite obvious he has not learnt any lessons yet. I believe there needs to be more consequence coming his way so he does learn a lesson. Unfortunately when he chooses to drive unlicensed (and therefore uninsured) , he poses a risk, not just to himself, but to the rest of the population who are at risk of losing a lot through no fault of their own. Even if he does get charged by police and pays the BMW guy cash for repairs, in my mind he has gotten off lightly when compared to what could have happened. ie he puts someone into a wheelchair etc etc.

Anto, Well I am glad to read that you enjoyed this thread. I see from your post that there may be some loss in translation possibly because you are not a local and although we all speak english, we use it in many different ways. I hope you don't mind but I have taken the liberty of rewording your post so it comes across a bit better when the average Aussie reads it..... Hello all from Anto, Well what an interesting topic!! There is a lot information to get through. Its awesome to see threads like this where people from a range of differing academic backgrounds come together and relay their experiences to discuss a topic that we are all interested in...Unlike topics such as 'nuclear' (tricky word to spell...) reactors as not many people actually have these and those that do are probably scientists. The details would be way too complex for most of us to understand anyway... There are not enough threads like this...98% of this thread brilliant and the remaining 2% (as usual) is from people butting in and making meaningless statements that do not relate to the topic at all. Wouldn't it great if people who had nothing constructive to say , actually didn't say anything at all... Very kind regards, Anto...

They also make for exciting discussions on SAU..

+1 from me on this... I always thought any cooling fan (clutch or electric fan) was there just to pull air through the radiator while the car was stationary or close to it. Road speed air would move heaps more air through the radiator than any fan behind it could. The intent of the clutch in the fan is to slip and therefore limit the fan rpm when engine rpms are high. The clutch is a simple viscous coupling which slips more as its temperature increases. Thats why when they are cold they slip less and as the oil comes up to temp, it slips more. When you get stuck in traffic and engine rpm drops, oil temp in clutch drops and it slips less..ie more drive to fan when it is needed.

Sorry mate I am a little lost. During the 'gear change' I am assuming that the exhaust gas pressure drop across the turbine (hot side) is very low and therefore very little energy is put into the exhaust wheel to keep it spinning. On thinking about it some more the would be some windage across the turbine wheel which would act to slow the T/C rpm. I am not sure if this was what you were getting at? The windage would be fairly low (I assume) due to the temperature of the exhaust gas (low viscosity) and also the smaller dia of the exhaust wheel when compared to the compressor wheel dia...

Aw FFS!! Nobody is saying that turbos go kaboom if you dont run a BOV!!! I am talking about long term wear on bearings and not catastrophic failures. By the sounds of it you guys are both running 'bush' bearing turbos???..So maybe your experience is based on those. Bush and Ball bearings can tolerate different levels of thrust loading. I think someone else in the thread supports this? Matt, As far as perpetual motion machines are concerned, your theory that reduction in turbine rpm is the same irrespective of BOV /NO BOV, to me, has a scent of divine energy creation in itself... By what you were saying I assumed 'you' had some measured data to support your theory. I was keen to see it. Onve agin very very simply put; On a gear change the only energy remaining in T/C is kinetic. Turbine starts to slow due to friction in brgs and windage etc. With no BOV, as soon TB closes there is a rise in pressure between it and the compressor. Now, where do you think the energy that compresses this air comes from?? Something else I will put out there. Another energy sink within the whole intake system is the restriction of the air filter and pipework leading up to the compressor. Typically the compressor draws air through this section of the intake and as a result, the pressure at the compressor inlet will be slightly -ve. (if you don't accept this I think I will call it a day-we must be using different brands of physics) Now consider that with a recirc BOV, the air is dumped back into the intake. So pressure within the intake will become slightly +ve and will therefore act to remove the intake restriction and IMO reduce the loss in turbine rpm...

Hammer and chisel to hammer it out!! ??? Maybe these are the only tools he can use properly. Is the socket in the head 'completely round'? Sometime you can get away with tapping (gently) an imperial hex driver that is just slightly bigger than the metric size. By hex driver I mean one of the attachments that you find in those screw driver sets you can get. Alternatively get an imperial allen key and cut it down. The you have something to grip onto with vice grips etc. OR If the top of the head is raised above the plastic enough you can use a dremel with a small circular blade to cut a slot across the top of the bolt then use a flat blade screw driver to turn it out. OR If you are confident enough you could drill the head out so that you can remove the cover. Then you should have better access to what remains of the bolt and use vicegrips to turn it out... Good luck with it...

So car manufacturers install BOV to meet emmisions???? How does that work?? Are you getting confused between vent to atmoshpere and recirculating? Were aftermarket BOVs created before OEM ones? Contradiction in terms? IMO aftermarket BOVs are made to satisfy the ever growing rice market out there.. Your large turbo would have higher KE...but it would also have more surface area on the impeller vanes (it moves more air right?) so the advantage backpressure would have over the impeller with respect to stalling it would be higher right? Now you have some proof that using/not using a BOV makes no difference to compressor stalling....but it does slow down right? Isn't the difference between it slowing down and stalling just a matter of time? Where is your proof? Please provide detailed explanation?

Wasn't there some interesting proof regarding this topic coming through today???

This just made my day!!! Well done there chap...

Not likely...When IC pipework comes apart, engine will idle but as soon as you give it any throttle, it will stall. Simple reason is air is not being drawn past AFM. Also when IC pipework comes apart you normally hear a significant pop...

Don't nearly all modern factory turbo cars run a BOV??..Europeans such as SAAB, Audi, Porsche, VW etc call it a 'compressor bypass valve'. They all use a Bosch item. Its what I use. I rate them, although there are a few forum members who claim they don't work. I must get special ones..

Adam..you are correct...and you? It takes one to know one?

I don't know much about the Neo ECU but what I do know is that with any AFM setup and a vent to atmosphere BOV, stalling issues are caused by the fact that when you close the throttle, the BOV is pulled open (all the ones I have used anyway) by the inlet manifold vacuum. The air drawn by the engine for idle and very light engine loads is then drawn in through the open BOV and not through your air filter and therefore the afm does not register that air. Obviously the extent to which this happens depends on where the BOV and air filter are in relation to each. Also depends on air filter restriction etc.. Also consider the fact that when you have 'vented to atmosphere', some air that has already passed through the AFM is dumped. So the ECU is calculating for air that the intake system no longer has...if this makes sense. I advocate plumb back all the time. I wont say anymore. With some smart tuning however you may get a driveable set up but if you want 'vent to atmosphere' consider a MAFless system.

I don't know that a turbocharger core would have a 'design factor' of 2??? ie stock Nissan RB25DET T28 stock application is 7-8 psi..They run fine at 14-16psi?? No The concensus is that they are 'ok' up to 11-12 psi and even then will not live a long life. So design factor is more like 1.5

Mmmmm, Just thinking about all the money that car manufacturers have wasted incorporating BOVs or compressor by-pass valves into their cars over the years..A BOV probably adds $50-150 to the build cost of each car. Millions of dollars wasted all because their engineers were liars....Can't trust those engineers!!!

I agree about the unidirectional thing. The direction of the force acting on the impeller vanes does not change. The rest of what you say I can't.. 1. Normal operating conditions where impeller is being spun by turbine. Air is drawn in at compressor inlet and starts to rotate with vanes. Air moves outwards through impeller (due to centrigual acceleration) and is captured by compressor scroll. Curvature of vanes acts to add tangential velocity to air as it moves into scroll. Velocity is in direction of air rotation in scroll which increases efficiency. 2. Under a reverse flow scenario, the air enters the scroll and obviously starts to rotate with it. As the cross section of the scroll reduces, the air is pushed into the vanes and starts to rotate them. The centrifugal force that is wanting to push the air back out is simply counteracted by the pressure in the scroll. You can prove this by getting an old turbo and putting compressed air into the compressor outlet. Believe it or not the compressor wheel spins backwards!! Also if you have a look at the geometry of the turbine, this is exactly how it works!! ie exhaust gas enters the scroll and turns the vanes. The only thing that changes is the vane geometry (curvature is the same though). Now we need to go back to basics.. When engine is running under boost the turbine is being spun by the exhaust gas. The turbine spins the compressor wheel and it compresses the air. On a gear change all positive pressure disappears from the exhaust manifold. It may actually be slightly negative due the fact that the exhaust gas flowing in the exhaust has inertia and wants to keep moving... So when the throttle closes there is no exhaust pressure to spin turbocharger because engine is not burning fuel. The only thing that is keeping it spinning is its own 'Kinetic energy'. It does not matter what the WG is doing. Without a BOV you have air pressure remaining in the compressor outlet which is trying to spin the comp wheel backwards and no energy from the turbine to counteract it (due to no exhaust gas pressure). It 'will' slow down quicker than it would if there was no pressure at the compressor outlet. Now as far as damage is concerned..There is confusion between wear and damage. Wear is a type of damage that occurs over time in an expected fashion. If a bearing gets through 15% of it expected life is it worn out or damaged? If it gets through 110% of its expected life is it worn out or damaged? What is known with certainty is that the life of a bearing is generally inversely proportional to its loading (all other things being equal)...The higher the loading, the quicker it fail. The is a very simplistic view but it gets my point across. Also if you are running 5psi and typical spikes were up around 15psi no issue. If you are running 25psi with spikes up to 50psi there may be an issue.. So when you dont run a BOV and you load up the thrust bearing more than what you would with a BOV, and it fails after 25,000km you may find it acceptable and call it worn out..If you were hoping for 100,000km then you would say its damaged....

Wilkor32gtr, Unfortunately mate you will not get a straight answer to this question on these forums. It has been debated for many years on these forums and comes up every few months. The pros and cons vary and actually depend many variables. The 'keyboards mechanics' out there have an endless number of anecdotes of cars that don't run BOVs have no problem. Race cars etc etc. Race cars are also not trying to get the best possible life out of their turbochargers though. (I assume you will be). Fact is some race cars also don't run cooling fans. But I can't ever remember seeing traffic lights and peak hour traffic on a race track. It really is a horses for courses thing. IMO, for a street car setup, a BOV is a very good idea for both turbocharger longevity and driveability.

Yes I think he means AFM... MAF stands for mass air flow.. The voltage output of the AFM is a bit larger than the range of 0-5v... The ECU sees its maximum as 5.12v because this is the highest voltage the A-D converter in the ECU can output. I would expect the afm output to be say 0-6v or 0-7v or something like that.. This is probably irrelevant though because if you are getting 8.2v at the signal when there is no air flow, the afm is indeed toast...With no air flow it should be at least under 1v.

Water into the AFM element would have stopped it from working properly.. AFM signal would have either gone to it lowest or highest output voltage. Most likely the highest. ECU would have seen this as excessive air flow and instigated 'air flow cut' cutting fuel and spark. This probably saved your turbo's compressor wheel from damage though. Large water droplets and spinning compressor wheel is not a good combination...The droplets may as well be ball bearings..

Most heater hose is not oil resistant and therefore over time start to swell due to the oil vapour in the intake air that they are transfering.. The genuine Nissan hoses would be oil resistant and last for years and years.. It may take years to become a problem and this depend on how much oil vapour gets into your intake. Turbo and engine condition etc will dictate this.. I would use heater hose as stop-gap measure until you find the right hose...Otherwise buy a few sets and treat them as a consumable...

Also check to see if either the r32 or r34 has a dictionary in it...

I 'think' it may be a case of early ECUs being quite sensitive to spikes and transients that may occur during a jump start...Now they are a very refined bit of kit and their sensitivity has been designed out.. So thats how this story may have started...

I"ll get my people to call your people...