BOV noises

Hello people,

I was just wondering how people get that multiple pssht pssht sound when just of throttle. Is it a sequential BOV or something else. Some guy told me that it is turbulance in the piping, but I think he's full of shite. Or is it the BOV bouncing?

Thanks heaps,
Doc

hi,

when i dont boost to max boost, and let off the throttle at about 3-5psi , i get the flutter sound, and so do most cars that dont hit full boost with a blowoff valve....

I think its because there is not enough pressure to completely open the valve and because oif that it just flutters a little bit...

also on rotors and other drag cars ive heard , they have external wastegates which i have been told (im reluctant to believe) that cause the same type of noise?

Rowan

G'day unfamilia,

Do you have a after market BOV or are y ou using the factory. Cause all mine does is pshht when the throttle is released regardless of how much boost is pumping. I really want that pssht pssht pssht sound, and I want it now god dammit.

Doc

sorry,

Forgot to mention i have a go fast bits aftermarket BOV - equivalent to turbosmart Type 2 bov i think..

Rowan

Unfamillia,
How dare you leave such an important peice of info out.
The only problem is that my mates RX7 made the similiar noice when before he got his BOV, and its not air going back into the turbo.

I'm f**ked if I know what it is.

Cheers big ears,
Doc

Originally posted by Doctor
Unfamillia,
How dare you leave such an important peice of info out.
The only problem is that my mates RX7 made the similiar noice when before he got his BOV, and its not air going back into the turbo.

I'm f**ked if I know what it is.

Cheers big ears,
Doc
Hey,
Its a sequential BOV. Standard BOV's will make a similar sound at half throttle but not as loud (not sure why tho) I just installed a GReddy Super Sequential and it makes that sound when you drive normally... if you full throttle her and let the car pull to 6-7k rpm then it just goes pssht. Also my standard BOV made a similar noise when not boosting to full... but the noise could hardly be heard and was a rather pathetic sound. :) hope it helps man

it also made the same noise with my stock BOV (although VERY quietly)

An R32 GTS4 i test drove at hill motorsports had a fluttering sound whenever i changed gears, regardless of the throttle/.boost position - maybe give them a call ? :)

Thanks ladies,

I appreciate the answers that you have supplied me with.
Unfamilia, didn't you buy a Skyline?

Doc

unfortunately not yet - the sale of my familia didnt go ahead, and im relying on that for the most part of my finance towards the skyline ..

soon to own r32.. soon :(

Oh man that sucks ass.
Oh well, good things come to those you wait. Geez I hate that saying.
Hope it comes soon buddy.

Doc

me too :)

:smoker2: :bloated:

Fellas,

The fluttering sound you talk about sounds like the noise most pod filters make when you back off before full throttle (ie before the BOV opens fully). I have a GFB BOV and I never heard that sound until I got the Pod filter installed. I have also heard cars with stock BOV and Pod filter making the flutter, and mine definately is the filter so maybe that's it.....


Brett

SOmeone correct me if I'm wrong but the fluttering is actually compressor chatter,

eg all the air is backing when the throttle body shuts and slamming into the compressor wheel. U tend to get it in aftermarket BOVs because they dont open unless you really cane it.

Er.. oh and its also bad for the turbo.

But the blitz ones flutter.. I dunno why.

ok if the fluttering noise isnt a sequential BOV then what is the difference between a Normal BOV and a sequential BOV (i always thought you got that noise coz the BOV let the pressure out in stages with a sequential BOV)

A sequential BOV works diffrently to ya normal BOV. It has 2 cylinders in it for one, and I think correct me if I'm wrong (has happened before) that it pulls the valves instead of the traditional push type.

Doc

My understanding is that a sequential BOV has 2 chambers. With single chamber BOV's you either have the spring loose so the BOV opens easier but can't vent as much air under heavy load, or tight to vent heaps but doesn't open as early (not really good). The twin chambers work by having a light spring on the first chamber and a heavier one on the second so you get the best of both worlds. But you pay for it....

I'm pretty sure that's the right explanation, but if anyone else knows for sure let me know:)

Brett

ahhh well there ya go then... learn something new everyday :licker: :licker: :licker:

gofastbits.com.au

The "Sequential" Myth
Added on 21st June, 2004

We’ve had a lot of enquiries recently beginning with the question “do you have the valve that makes that sequential noise?”. There is a common misconception that the fluttering, chirping kind of noise that people often hear, is caused by a sequential valve. This is NOT correct, in fact, there is no such thing as a blow-off valve that makes this kind of noise.

The term “sequential” is applied to HKS’ Super Sequential because it has two valves that open one after the other, the small inner valve opens first, which then pulls the second, larger valve open. By this definition, GFB’s Hybrid, Bovus Maximus and Stealth FX valves are also sequential, as there are two ports, which open one after the other.

The fluttering noise is in fact compressor surge, caused by pressurised air blowing back through the turbo when you close the throttle. Compressor surge occurs when the blades of the compressor “slip” in the air, much like an aeroplane wing stalling. This condition is most common when shutting the throttle and not opening a BOV far enough, but it can also occur with the throttle open under boost conditions if the turbo is not correctly matched to the engine. The fluttering noise is simply a result of the pressurised air trying to escape through the turbo, and the turbo attempting (under its own momentum) to cram it back in. The high velocities of the air involved can sometimes make a chirping noise in combination with the flutter.

Whilst the noise does not actually come from the blow-off valve itself, it can be caused by the blow-off valve. When the spring pre-load is set too hard, or the valve itself cannot flow enough air, compressor surge will result. Generally, if the spring is too hard, you will tend to hear the surge at low to medium RPM and boost conditions, with a normal “whoosh” at higher engine speeds and boost. If the valve is too small for the task, the surge will occur at high RPM and boost.

It is possible for the blow-off valve to open and still cause surge, as at lower RPM and boost the compressor is closer to the point of surging. Turbos can surge even with the valve half open at low RPM, and yet at high RPM even with the same valve opening, it does not surge. If you’ve ever watched the piston of a blow-off valve open when the turbo surges, you’ll usually see it flutter up and down, which is what leads people to think it is the valve causing the noise. It is in fact the pressure fluctuations in the turbo piping caused by the surge. If you hook a boost gauge near the turbo, you can see the pressure fluctuating as the compressor surges.

Ok, so how do I get that noise, then?
Quite simply, all you need to do is increase the backpressure in the turbo piping when you lift off the throttle. This can be done by removing the valve totally (not recommended – see paragraph below), or adjusting the spring on your valve harder. This will allow the valve to open at higher RPM and vent normally, and at low RPM will increase the amount of air flowing back through the turbo.

However, the noise that you get is totally dependant on your individual engine/turbo/intercooler/air filter setup. A stock intake air filter box will usually muffle the noise very significantly, pod-type filters will make the noise much more obvious. Secondly, the noise is very dependant on the type of turbo. Usually you will find that smaller turbos such as the TD04 used on WRX’s will not surge as readily, and do not sound the same at all. Nissan turbos such as those used on the 200SX and GTS-T readily surge at low RPM (accelerate moderately to about 3000 RPM, roll off the throttle, and you’ll usually hear it on a Nissan). Larger intercooler set-ups also increase the chance of surge, as there is a significantly larger volume for the valve to evacuate.

So if the noise is compressor surge, will it wreck the turbo?
This is a very grey area, dependant on too many variables to say yes or no. Generally, if the surge is only occurring at low RPM and boost, then there really isn’t going to be a detrimental effect on the turbo. You only need to compare the loads placed on the turbo at full boost near redline to the small amount of surge at low RPM to see this. If the surge is occurring when you are driving flat out at high boost (greater than stock), then the risk of turbo damage and/or a reduced turbo lifespan is greatly increased. Also bear in mind that driving style alone probably has the greatest effect on the life of your turbo!

ive got a sequential BOV and it flutters, but when i got my pod filter, it made the flutter alot more prominant. also cars that are using such things as link computers, or any thing that allows to take out the air flow sensor flutter real loudly.

In reaction to Turnerl.
The fluttering is highly unwanted. Although it sounds cool.
Surge can wreck the blades of the compressor. This happens mainly at high rpm's (of the compressor) and low air mass. This is why the bov is designed in the first place. The main function is to increase the air mass that will go through the turbo and keeping it away from the surge line. Besides that the older model turbo's have 270 degree bearings. When the compressor is driven the turbo shaft is pushed one way. When the throttle is closed the turbo is pushed the other way and it depends on the setup of the engine how it gets to the other side. This is off course no problem for the 360 degree bearing turbo's.

Derby

all you have to do tighten up your b.o.v as much as you can to make that flutter noise its quite simple really