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Discussion Starter · #1 ·
I just noticed my BOV is open at idle then as soon as I touch the throttle it closes. I've did some searching and some people say it is ok and just put a filter over it, others say put a stiffer spring in so it stays closed at idle. What do you guys think?

I'm also thinking this could be causing my lean take off problem. At idle it seems like air is getting blown out of the BOV. So when I first get on the gas and it shuts, that would cause extra air to be pushed into the engine. I'm thinking if it is shut all the time it wouldn't have a rapid change in air flow.
 

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I can't speak for all BOVs and I know you don't have the same as me, but in my experience an open BOV at idle could cause idle problems. That doesn't explain lean take off though.

I'd be interested in seeing if your maf is too close to the throttle body. If too close, the maf will read the air as unstable and would cause acceleration problems.

EDIT: Looking at your pics, it's not sitting right on top of the throttle body, so chances are it's probably ok. Ya got me. :)
 

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It's not supposed to be open at idle
 

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Discussion Starter · #4 · (Edited)
Thanks for the help! Looks like you're suppose to pick the BOV spring based on the vacuum at idle. Here is the chart from Tial's web site on the 50mm BOV:

Engine Vacuum_______Color________Use Spring
---------------------------------------------------------------------------
- 22 and -23 in/Hg______Pink________12 Psi (-24 in/Hg )
-18 and -21 in/Hg______Un-painted___11 Psi (-22 in/Hg )
- 14 and -17 in/Hg______White_______-9 Psi (-18 in/Hg )
-10 and -13 in/Hg______Black_______-7 Psi (-14 in/Hg )

My vacuum is around 14.5 in/Hg according to my FIC so it looks like I need to go up to the 9psi spring. Hopefully this helps my takeoff problem.
 

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Discussion Starter · #6 ·
Right now I have the Tial 50mm BOV with a 7psi spring. I just ordered a 9psi spring.
 

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EL NINJA MODERADOR
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You have a great set up ;)

BTW
try to dedicate a vacuum hose not "T" for the BOV, if that solve the problem then you can find on Ebay Vacuum blocks, they are a better way to have all connected.


 

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Discussion Starter · #8 ·
Major mistake on my part! I haven't looked at my FIC software for months and for some reason thought my AFR of 14.5 was my vacuum in in/Hg. .:doah: Waaaaay off. So needless to say that the 9 psi spring didn't work and the BOV still open a little at idle.

So now after actually looking at my FIC the vacuum is 10 psi (20.4 in/Hg) at idle. So the 11 psi spring is what I really need and is on its way. There goes $40 down the drain for being ignorant
 

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Dedication to Thai Cuisine
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WHY DID NO ONE CATCH THAT FOR HIM! also, at least you know know the problem, if the 9 psi spring helped a little.
 

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Discussion Starter · #10 ·
I got the 11psi spring today and it appears to be too stiff. The BOV now flutters when it goes off. I tried making a vid of it but it but I couldn't hear it very well when I played it back.

My plan now is to go back to the 9psi spring and add some washers to space it up a little. When I had the 9psi spring in the BOV was only open about an 8th of an inch so it shouldn't take much to get it right. Do you guys think this is the best solution?
 

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Discussion Starter · #12 ·
It is a Tial 50mm. It doesn't have any adjustment on it.
 

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Discussion Starter · #14 ·
Thanks for the help! I'll try to find some washers tomorrow and space the 9psi spring a little. Hopefully I can get it to stop surging and stay closed at idle.
 

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Discussion Starter · #16 ·
I found a washer at Lowes that worked pretty well but using it with the 9psi spring still caused some surge. It isn't as bad as the 11psi spring but it still surges some. It doesn't surge when I let off at full boost (3psi) but it does when I'm around 1psi of boost and a little bit in vacuum as well.

I read some people say some surge is ok at low boost levels. Do you guys think that would be ok?

The washer I used was kind of thick so I might try to find a skinner one. I was stupid and didn't look to see if the 9psi spring and washer made the BOV stay closed at idle. I just drove it and heard the surge then took the washer out. I'll have to play around with it some more tomorrow.

Another thing I just thought of is that I put the washer on the part of the BOV that moves. I wonder if the extra weight could cause it to surge more since it will not move as fast. I might try putting it on the other end but there isn't a big enough lip to hold both the washer and spring in place, so that might not be possible.
 

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there is no reason why it would stay closed at 3 psi and open up at 1 psi... something's hooked up wrong, maybe?
 

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Discussion Starter · #18 ·
When I'm at 3psi of boost then let off the throttle the BOV sounds like it works correctly but just opening once. But if I only boost up to 1psi then let off the throttle the BOV sounds like it open and closes a few times, like it is fluttering.
 

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Discussion Starter · #19 ·
The washer I tried the other day was 1/8" thick. I found some skinner ones that are about 3/64" thick. So about a third the size.

I put one of those in with the 9psi spring and put it in the housing of the BOV, not the part that moves. At idle it is still open a little, maybe an 1/8". I then drove it around and the BOV is going off twice when I let off the throttle at around -5 to -10 in/Hg vacuum. When I let off from -5 in/Hg vacuum to 3psi boost the BOV goes off once like it's suppose to.

So how bad is it that it is fluttering like that low load levels? I assume it is bad for the turbo but at those low of levels maybe it is ok. Is there some magic level that it is ok to have the fluttering of the BOV?

What about putting a filter over the BOV so it doesn't suck in anything bad and just live with it open slightly at idle? It runs fine with just the 9psi spring so that isn't an issue.

Any help would be appreciated!!! :3_shiny:
 

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Discussion Starter · #20 ·
I've been reading a lot on this the last hour and so far this is the best info I've found. It sounds like the flutter is ok at low RPMs but bad at high RPMs, which is what I'm seeing.

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!
 
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