How Blow Off Valves Work

[69Marshall69]

I have the wonky idle issue when I place a soft enough spring for BOV to open at idle. Now I usually run a stiffer spring causing the BOV never to open but that's dangerous for the turbo shaft/bearings. Now this MAF sensor is obviously too close to the BOV on the FBM kit to run like it normally should, so other than high speed density change is there another way around this problem?

[crazyfrenchbiker]

Originally Posted by 69Marshall69

I have the wonky idle issue when I place a soft enough spring for BOV to open at idle. Now I usually run a stiffer spring causing the BOV never to open but that's dangerous for the turbo shaft/bearings. Now this MAF sensor is obviously too close to the BOV on the FBM kit to run like it normally should, so other than high speed density change is there another way around this problem?

Never open, even under boost?

How much boost are you running? Which BOV? Do you have a boost gauge, if so, what are you running vacuum at idle and at WOT?

Also, respect for a car from the 902 - Was just there a few weeks ago visiting my parents.

[King Tut]

Originally Posted by 69Marshall69

Now I usually run a stiffer spring causing the BOV never to open

Never is a long time. I don't know why your car is different than every other Full Blown car. My BOV worked perfectly with an 11 psi spring. If yours isn't opening then there is something else wrong and my guess would be the vacuum/boost source you are providing to the port on the BOV.

[mike the snake]

I have read some people say that at low boost levels a BOV isn't as necessary. Yes, you'll get the surging, but it isn't as destructive at low boost pressures.

[Sellout]

Originally Posted by mike the snake

I have read some people say that at low boost levels a BOV isn't as necessary. Yes, you'll get the surging, but it isn't as destructive at low boost pressures.

That's why Greddy's low boost turbo kits for non-turbo cars almost never include a BOV.

People will argue about it because "omfg the OEMs use them so they must be necessary", but the OEMs aren't typically running 7 psi boost these days...

[69Marshall69]

Nice to see someone come by the east coast from this site haha Well my FBM kit came second hand from a guy in Jersey, I never changed anything from the kit and my vacuum source is what was recommended by FBM. after WOT my vacuum is -21. now the spring I have in my BOV is designed for -24 to -27 therefore the BOV never opens. I put a softer spring in (9lbs) and it stayed open during idle (which is apparently what its supposed to do) but MAF sensor was misreading causing a wonky idle. so I went with a slightly stiffer spring, now the car still idled a little funny as the BOV would continuously open and close because my idle vacuum is so close to my WOT vacuum, around -19 to -20. so I consulted with a few people and they told me the BOV is too close to the MAF sensor and it should be relocated further down the pipe. I wondered why such people who knew what they were doing when they designed this kit, would not realize this potentially fatal flaw. Then I found out this car runs on both MAF and MAP sensors. A buddy of mine told me in order to run the kit correctly, I would need a MAFless Tune and upgrade my MAP sensor in order to up the boost. I currently have 7psi for boost (wastegate spring) in my car so its safer to have the compressor surge compared to a higher boosted engine, but before I increase my boost im solving this BOV situation.

[69Marshall69]

i now have the 11lb spring but it would slightly open and close causing an idle issue, the BOV would release but i would get a compressor surge right before it would. maybe all i need is a washer to stiffen the spring ever so slightly but the cars BOV should be open at idle due to stand BOV operations. I may be wrong but the BOV should always release once any time of vacuum is created. where did you tap off for vacuum?

[SilverSkyline210]

[ame="https://www.youtube.com/watch?v=sLr1A9Duwck"]R34 GTR HKS T51R - YouTube[/ame]

[sw20kosh]

Originally Posted by 69Marshall69

i now have the 11lb spring but it would slightly open and close causing an idle issue, the BOV would release but i would get a compressor surge right before it would. maybe all i need is a washer to stiffen the spring ever so slightly but the cars BOV should be open at idle due to stand BOV operations. I may be wrong but the BOV should always release once any time of vacuum is created. where did you tap off for vacuum?

No a BOV should only release when there is boost in the charge pipes and the throttle plate shuts (causing the intake manifold to have vacuum). The line to your BOV should be from the intake manifold.

[69Marshall69]

Yes I understand that, that's where my vacuum is drawn from. But the car idles close to its maximum vacuum causing the BOV to open. most BOVs operate at any negative pressure to counteract any compressor surge. when I had the 11lb spring, I would get a slight compressor surge right before my BOV would open. this is because the vacuum pressure took a split second to reach max negative pressure. so im assuming that if I ran a lot more boost, my turbo would still get a compressor surge and would be dangerous enough to cause major damage. I think a MAFless tune is the only answer unless the BOV is relocated


remember, at idle the car is in vacuum

[sw20kosh]

Originally Posted by 69Marshall69

Yes I understand that, that's where my vacuum is drawn from. But the car idles close to its maximum vacuum causing the BOV to open. most BOVs operate at any negative pressure to counteract any compressor surge. when I had the 11lb spring, I would get a slight compressor surge right before my BOV would open. this is because the vacuum pressure took a split second to reach max negative pressure. so im assuming that if I ran a lot more boost, my turbo would still get a compressor surge and would be dangerous enough to cause major damage. I think a MAFless tune is the only answer unless the BOV is relocated


remember, at idle the car is in vacuum

You don't want a MAFless tune. Your car will not drive right according to tuners.

On the Ptuning gt3076 kit the BOV doesn't even blow off unless you are running upwards of 6psi. Compressor surge all day long unless you up the boost. It disappears as long as you have 6+ psi of boost in the pipes. The higher boost I run the louder the BOV release gets and 0 surge.

I talked to the kits designer and he said I could run with a very weak spring if I wanted since the MAF is so far away from the BOV and there is an intercooler in between them. Maybe relocate your BOV?

[King Tut]

Originally Posted by 69Marshall69

Yes I understand that, that's where my vacuum is drawn from. But the car idles close to its maximum vacuum causing the BOV to open. most BOVs operate at any negative pressure to counteract any compressor surge. when I had the 11lb spring, I would get a slight compressor surge right before my BOV would open. this is because the vacuum pressure took a split second to reach max negative pressure. so im assuming that if I ran a lot more boost, my turbo would still get a compressor surge and would be dangerous enough to cause major damage. I think a MAFless tune is the only answer unless the BOV is relocated

How are you sensing this "slight compressor surge"? What boost level are you actually running right now? You need to do whatever your vacuum source/BOV needs to keep it closed at idle. That will most likely be an 11 psi spring, but if you still have some issues then try a couple washers. I will mail you the ones I used if you want. Remember the sole point of that spring in the BOV is to keep it closed at idle in the highest vacuum situations. That is why they are rated in terms of vacuum. Don't get obsessed with some percieved sense of compressor surge. If you no longer want to deal with this, then I would recommend spending the money to relocate the BOV down into the driver side fog light area.

[zoth]

Originally Posted by audixieboy

man, sorry if I hurt your feelings man. Take it you feed your family by selling expensive BOVs. Was just asking a question. Thanks for response. ****

In short... any cheap imitations will leak=loss in performance & possible engine damage should you decide to go FI.

[69Marshall69]

Thanks for the pointers guys, it could even be a tuning thing. I will give the washer idea a go with the 11lb spring. I get the whole vacuum thing and I figured FBM knew what they were doing. I just had a lot of tuners tell me that it needed to be relocated if running a MAF so close the BOV. my max vacuum is so close to my idle vacuum is why I was overthinking the entire situation. One tuner just scared me with the whole compressor surge dilemma. Because this is a whole new world to me I get sketched out when people say these things. Which is why I consulted you guys
im running 7psi boost right now and about the slight compressor surge, I was referring to a compressor surge right before my BOV would release ( this was with the 11lb spring) thats all I was talking about. King Tut if you wouldn't mind showing me a picture of the washers, im going to try and find some tomorrow or machine the proper size (how many did you end up using and what was you vacuum levels at max and idle) thanks!