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Discussion Starter #1
Ok I run a safari snorkel and 3 inch exhaust. I know they both amplify the induction sound, but a couple days ago I noticed a sound I have not noticed before. I'm told it's normal but not so sure.. during gear change and while under load it makes a 'whoosh' sound. It also makes that same sound very vaguely when I gear down.

I have changed the air filter, checked hoses and exhaust flanges.. they're all ok

2013 3l crd 37xxx kms
 

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Discussion Starter #3
haha that's what my old man said also. I think you're both right
 

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LED ZEPPELIN
1995 GQ TD42 NA
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I'd agree with that, when I had my 2008 with Safari snorkel and 3" exhaust I'd occasionally wonder if I was hearing something a bit weird, but I never had any problems.
 
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I SUNK 1
Nissan Patrol ST GQ30
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sounds to me like a bit of turbo blow back (hope thats the right word) do you run a blow off valve (even a recirculated one)
 
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sounds to me like a bit of turbo blow back (hope thats the right word) do you run a blow off valve (even a recirculated one)

Now whilst you can get a blow off valve for a diesel, I dont think he has one. It is compressor surge... normal
 

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Y2KGUII ZD Wgn
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Compressor surge is a dangerous thing if left to continue, it can destroy bearings etc, I doubt it is surge on your ZD30 VNT, just the normal intake sound amplified by the snorkel, after removing the screens from my airbox lid this sound was amplified a little more, but still acceptable, I quite like it. I get a nice whistle and a slight whoosh and I'm running over 18psi without surge.

Surge will see a slight drop in boost in cycles as the turbo beats and then meets demand until maximum boost is reached.
 

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Y61=WIN
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Yes it wont be compressor surge. Ive been trying to get my hands on the compressor map for the CRD Y61 compressor wheel so I know for sure exactly where compressor surging will occur. I know for a fact it wont surge at 27 psi and the airflow rates the engine see's Ive been running that years now. I dont know how much beyond 27 psi itll do before surge I dont want to be an expensive genuine pig :)

Since diesels arent throttled you dont get the "pressure surge" (for want of a better term not compressor surge but the rise in pressure when the throttle slams shut) of airflow and things like a blow off valve dumping it in petrol engines. But you still get some pressure and airflow changes in diesel engines as revs change and load changes etcetc so you get those little noises in the intake system from it, its all normal
 

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Y2KGUII ZD Wgn
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Edzackery. A few years ago I had the boost line suddenly develop a small split on the back of my high pressure Dawes and boost shot to 26psi, at the time (on the side of the Motorway) I could not find a cause so drove home around 40k so I could look at it in detail, there was no surge experienced while doing that and my spoolup (the main offender for surge) was as aggressive then as it is now. Limp yes, surge no.
 

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Y2KGUII ZD Wgn
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Discussion Starter #14
These relate to Gas engines but the same principles apply, a turbo doesn't need to be at full boost to get surge, it can happen on it's way there, it is simply too much air coming in that cannot be used by the engine at that specific moment.

From the horses mouth:

https://www.turbobygarrett.com/turbobygarrett/compressor_surge

and a second opinion, with some interesting observations:

http://www.gfb.com.au/tech/tech-articles/11-the-truth-about-compressor-surge
Thanks for that
 

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Y2KGUII ZD Wgn
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Discussion Starter #17
great info guys, but I'm still curious as to how that can start on it's own a couple months after owning her. It is a sound I would have definately noticed at the start
 

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Discussion Starter #18
sounds to me like a bit of turbo blow back (hope thats the right word) do you run a blow off valve (even a recirculated one)
I don't have a blow off valve. They worth getting?
 

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I SUNK 1
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compressor surge was the word i was looking for too :cool:. from what ive learnt compressor surge is created when the throttle closes and the excess air created has no where to go but flow back to the compressor wheel causing it to effectively stall creating the noise. a blow off valve lets this excess air out. a recirculated bov puts the excess air back into the intake and starts the compressor wheel truing thus making it more efficient to some extent.
from what i was told this is no problem and wont do any damage when running low boost as things arent spinning as fast as the could be. in regards to a blow off valve, again i was told running only 10psi it isnt really necessary. i have run with out one so far but being a race car, i am going to install one as i am constantly on and off of the throttle so i think the frequency factor will damage it. where as on a road car throttle on and off happens slower and less frequently so would be less likely to do damage.

please note, i am far far from an expert. this is only what i have learnt and may not be correct.
 
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