Weird flutter/ surge?

[Callumgw]

I think there is a lot of people who believe the sound that is made by the BOV is surge. When the BOV return is placed near the filter or opened to atmosphere the sound of air coming out is heard. Now this often pulses making that distinctive sound. But the sound is only a symptom of pressure fluctuations in the inlet, not a certainty of surge. You may be getting it but it isn't a certainty. If the BOV is doing it's job properly the compressor should not reach the stall conditions, despite the noises of the BOV.

Also surge will shorten the life of your turbo. Guaranteed. It place more load cycles on the unit that are at the upper design range and over time it will have an effect. Remembering that turbos can last 200000km plus, so half a year or even 2 years isn't a long test, nor an indication that it "has no effect"

So if you have short term objectives it's not likely to give you a problem on a new turbo. If you have an older turbo it just might.....

C

[xr6eta]

cool, thanks. What does engine ping/ knock actually sound like? i think i wound the boost up too much last night hahaha

Hey TimmyET

You sound like you're having fun with your new toy, I just got one of those in the mail yesterday, haven't fitted it yet as DAMO is helping out with the LT10x fitment so doesn't matter yet. Just noticed most responses were in relation to flutter or surge sounds and not your ping/knock question. I know very little about these cars bar what I've learned on this forum and it sounds like you're playing with danger not having an intercooler and winding the boost up a heap. From your 9ish answer to the boost pressure it doesn't even sound like you have a boost gauge (how do you know 9ish). I don't know what pressure these little boost thingies go to but to save fitting a new engine, you might want some more advice from people on here. Just a suggestion.

[ETONE]

I think there is a lot of people who believe the sound that is made by the BOV is surge. When the BOV return is placed near the filter or opened to atmosphere the sound of air coming out is heard. Now this often pulses making that distinctive sound. But the sound is only a symptom of pressure fluctuations in the inlet, not a certainty of surge. You may be getting it but it isn't a certainty. If the BOV is doing it's job properly the compressor should not reach the stall conditions, despite the noises of the BOV.

Also surge will shorten the life of your turbo. Guaranteed. It place more load cycles on the unit that are at the upper design range and over time it will have an effect. Remembering that turbos can last 200000km plus, so half a year or even 2 years isn't a long test, nor an indication that it "has no effect"




So if you have short term objectives it's not likely to give you a problem on a new turbo. If you have an older turbo it just might.....

C

i dont think the would be much stress going on at 7-12 psi Callum, i've talked to alot of big hp boys in the skyline world and the same answer pops up all the time " you only need a BOV for big boost" thats if your worryed about turbo wear... are we forgetting what BOV's are really for ........


Campbell

[Callumgw]

i dont think the would be much stress going on at 7-12 psi

answering this simple statement isn't that simple, because when things are designed there is several thing consider. First can it survive the biggest load predicted? then if the answer is yes, can it survive for the period required under the series or repeated loads. These load cause fatigue and fatigue occurs at much lower stresses. For steels the endurance limit, below which very little fatigue occurs, is down towards 30% of maximum stress. So even at low stress the item is consuming life.

We should also mention thermal stress because that plays a part.

Now lets think about stress verses load. The stress has to do with the amount of material that carries a particular load. We also need to consider the effect of stress concentrators. So if we think about three wires all made of the same material. The first has a diameter and the second has twice the diameter. Because stress is load by area the thicker one can carry a bigger load. The stress inside is less and doesn't reach the ultimate stress on the metal. the third wire is as thick as the first but has a notch, even at the notch it has more area than the first wire. It could actually break befoe the first wire (despite more area) because of the stress concertation created by the notch.

So stress and load are related, but you don't know the stress unless you know how the designer built something. Fatigue is driven by stress and as such concentrator make things worse, worse again than for static loads.....

So lets get back to the big turbo boys...how many break turbos and then fit a bigger one? how many have a turbo that lasts 100,000km? or 50,000km?or even 10,000km?I don't think they can talk about longevity and life. They may be able to say it'll last 30 dyno runs and 10 drags at 30 psi....but what abut normal use?

In short. BOVs are good they reduce shock loads on turbos. Surge is bad it causes shock loads on turbos. A large amount of bigger loads = less life. Almost guarenteed.

C

to explain the "almost" exceptions will take another little while...

[Damo]

i dont think the would be much stress going on at 7-12 psi

answering this simple statement isn't that simple, because when things are designed there is several thing consider. First can it survive the biggest load predicted? then if the answer is yes, can it survive for the period required under the series or repeated loads. These load cause fatigue and fatigue occurs at much lower stresses. For steels the endurance limit, below which very little fatigue occurs, is down towards 30% of maximum stress. So even at low stress the item is consuming life.

We should also mention thermal stress because that plays a part.

Now lets think about stress verses load. The stress has to do with the amount of material that carries a particular load. We also need to consider the effect of stress concentrators. So if we think about three wires all made of the same material. The first has a diameter and the second has twice the diameter. Because stress is load by area the thicker one can carry a bigger load. The stress inside is less and doesn't reach the ultimate stress on the metal. the third wire is as thick as the first but has a notch, even at the notch it has more area than the first wire. It could actually break befoe the first wire (despite more area) because of the stress concertation created by the notch.

So stress and load are related, but you don't know the stress unless you know how the designer built something. Fatigue is driven by stress and as such concentrator make things worse, worse again than for static loads.....

So lets get back to the big turbo boys...how many break turbos and then fit a bigger one? how many have a turbo that lasts 100,000km? or 50,000km?or even 10,000km?I don't think they can talk about longevity and life. They may be able to say it'll last 30 dyno runs and 10 drags at 30 psi....but what abut normal use?

In short. BOVs are good they reduce shock loads on turbos. Surge is bad it causes shock loads on turbos. A large amount of bigger loads = less life. Almost guarenteed.

C

to explain the "almost" exceptions will take another little while...

I don't disagree with most of what you are saying Callum, you are more than likly correct on the stress and fatigue issue, but I am still to see a turbo fail due to throtal closed surge. As has been said before, I would suspect that more than 80% of manufacturers reasoning behind BOV's is NVH rather than turbo longevity. Esspecialy in this day and age of materials.


Damo

[ETONE]

Callum,

You didn't answer my question :p

What are BOV's really for?????

And just a lil FYI, i have a mate his name is Matt he has a R32 GTR pushing 400kw atw and has done for the last 40000kms and no BOV (only cause he hasn't found one he like yet such a poof) but thats 22psi everyday and no signs of bad shit yet.
I agree with you BOV's reduce wear but how much?? I think it would be insignificant on the amount of boost the boys on this forum run.

Campbell

[ETONE]

i dont think the would be much stress going on at 7-12 psi

answering this simple statement isn't that simple, because when things are designed there is several thing consider. First can it survive the biggest load predicted? then if the answer is yes, can it survive for the period required under the series or repeated loads. These load cause fatigue and fatigue occurs at much lower stresses. For steels the endurance limit, below which very little fatigue occurs, is down towards 30% of maximum stress. So even at low stress the item is consuming life.

We should also mention thermal stress because that plays a part.

Now lets think about stress verses load. The stress has to do with the amount of material that carries a particular load. We also need to consider the effect of stress concentrators. So if we think about three wires all made of the same material. The first has a diameter and the second has twice the diameter. Because stress is load by area the thicker one can carry a bigger load. The stress inside is less and doesn't reach the ultimate stress on the metal. the third wire is as thick as the first but has a notch, even at the notch it has more area than the first wire. It could actually break befoe the first wire (despite more area) because of the stress concertation created by the notch.

So stress and load are related, but you don't know the stress unless you know how the designer built something. Fatigue is driven by stress and as such concentrator make things worse, worse again than for static loads.....

So lets get back to the big turbo boys...how many break turbos and then fit a bigger one? how many have a turbo that lasts 100,000km? or 50,000km?or even 10,000km?I don't think they can talk about longevity and life. They may be able to say it'll last 30 dyno runs and 10 drags at 30 psi....but what abut normal use?

In short. BOVs are good they reduce shock loads on turbos. Surge is bad it causes shock loads on turbos. A large amount of bigger loads = less life. Almost guarenteed.

C

to explain the "almost" exceptions will take another little while...

I don't disagree with most of what you are saying Callum, you are more than likly correct on the stress and fatigue issue, but I am still to see a turbo fail due to throtal closed surge. As has been said before, I would suspect that more than 80% of manufacturers reasoning behind BOV's is NVH rather than turbo longevity. Esspecialy in this day and age of materials.


Damo

Yay Damo answer first you lose callum
just playing

Campbell

[BennyET]

You didn't answer my question :p

What are BOV's really for????

Campbell

i'd say drivability and nvh [noise vibration harshness] as fitted from factory

i really noticed a diffence on my et when i removed the bov, between gear changes the revs would drop more slowly through the flutter and had to time the clutch differently to change as smoothly as when the bov was on. would much prefer a valve on; recirc or venting definitely made a difference for me

[Callumgw]

I don't get te NVH issue at all. I've had turbo with and without and frankly didn't notice any NVH issues.

The two things a BOV does is keep the turbo spinning to improve response by reducing spool time. And at the same time this reduces the load range and will extend life. So to increasing mid range response and driveability (with other load side effects) is what I think BOVs are really about for manufactures. This way people stop complaining about lag and response of new turbo cars.

My opinion anyway.

C

[TimmyET]

Its all a bit more than I needed to know but thanks I guess. Everyone. Hah