does blow off valve location matter?

[S14tat]

well ever since i upgraded my turbo to a T04E, the car's been fluttering. even when i took out the springs, and run the type S with boost assist, it still flutters. now the problem is that the type S use to be located 6 inches away from the compressor discharge. but since the T04E's housing is waay different from the B's i had to get the pipe cut and that ended up shifting the type S to only 2-3 inches away from the discharge. do you think theres too much turbulance there thats why i'm gettin the fluttering no matter how i run the thing?

[Structure240sx]

possibly so close that it cant bleed the air fast enough either. move it

[Import_Ant]

possibly so close that it cant bleed the air fast enough either. move it

^that sounds probable. another aspect to take into consideration is heat. you could relocate the BOV to the cold pipe and it would help it last a bit longer due to the decrease in the heat you are exposing the valve to. it's not a HUGE issue but something to take into consideration if you are going to have to relocate the BOV anyhow.

[GirlsLoveBoost2]

Best place to mount the bov is as close to the throttle body as possible, reason being to avoid the flow of air to be reverted back through the IC..basically the air from your turbo is being forced down through your hotside piping then through the ic then the cold side piping up twards your throttle body then when your throttle slams shut the air is trapped and needs a way to get out (BOV) you dont want the air to backtrack through the ic piping toward your turbo b/c then when you open your throttle back up you have to reverse that air again..the closer the bov to the throttle body the less backtracking the air has to do...that might be why your bov is fluttering......What are you using as a vacuum source for the top nipple of your bov? And how many other things are teed off of that source? Having a good clean single purpose source for your bov will also help, even though the KA doesn't have many vacuum source options.

Hope that helps.

[nissanfanatic]

A little surging right as you let off the gas is no big deal. Its very common on large compressors such as the T04E.

[S14tat]

well it worked perfectly fine before in its old location. also i dont' want to deal with all that extra plumbing to route the boost back into the intake from the cold pipe. and like i said before, since it worked perfectly fine before on the hot pipe. i dont' think its fluttering because i have it on the hot pipe.

i have the signal Tee'ed off from the FPR. but i also have my boost gauge and wastegate Tee'ed off the same line. but like i said before, it worked fine before with that same setup. but i will buy a vacuum manifold when UR comes out with it so i can just use one single and have a large collector with many different ports to Tee off too.

[C-Kwik]

Best place to mount the bov is as close to the throttle body as possible, reason being to avoid the flow of air to be reverted back through the IC..basically the air from your turbo is being forced down through your hotside piping then through the ic then the cold side piping up twards your throttle body then when your throttle slams shut the air is trapped and needs a way to get out (BOV) you dont want the air to backtrack through the ic piping toward your turbo b/c then when you open your throttle back up you have to reverse that air again..the closer the bov to the throttle body the less backtracking the air has to do...that might be why your bov is fluttering..

I have yet to see hard data to support it either way. But, my own speculation is that before the IC would be better. There is higher pressure there so the BOV should be more responsive. The BOV does not need to prevent reversion and frankly reversion would only occur if you let the pressure drop. A BOV only needs to allow the turbo to flow enough air when you close the throttle to prevent the airflow at the turbo from falling into the surge area. Ideally, you want the pressure to remain in the system so that boost response just after the shift is better. In this kind of set-up, either will work fine, but for maximum response, I would think it would be better to have it before the IC.

As for the flutter, I had it in my KAT and the BOV was mounted after the IC.

[Structure240sx]

people are talking about different things fluttering

it is the turbo fluttering (compressor surge) that we are talking about not the bov fluttering

like cory said its very common to have very light surge (fluttering) under certain conditions

[nissanfanatic]

Surging and fluttering are two different things..

If you have flutter, that means your BOV is adjusted too tight. Fluttering is when the valve is opening and closing constantly... You would hear a pssh pssh pssh pssh.

If you have surging, that means that your BOV is either undersized, not reacting quick enough, or is adjusted too tight. Compressor surge for me actually sounds a lot like my BOV is fluttering, but luckily, they are on different sides of the car, so I can tell which is which. I get a "chsh chsh psshhhhhhhhh"

I have also ridden in cars where the BOV was mounted before the IC and I have to say, I have way better boost response after shifting.. Zero lag after a shift..

[scarboroughdub]

I have yet to see hard data to support it either way. But, my own speculation is that before the IC would be better. There is higher pressure there so the BOV should be more responsive.

hard data you may not get but from experience i have worked on several cars and they showed stumbling problems and bad idle if the bov was located close to the turbo, but being close to the throttle body would help to issues greatly.

as for the bov response time, it doest matter where it is because the vacuum source is coming from behind the throttle body or the manifold, so there for the bov being close to the throttle body would yield a shorter vacuum line going to the bov.

[2_Liter_Turbo]

Also consider where OEM's put the BOV. On the S13 Sidemounts, their stock BOV is located after the intercooler. On DSM's it is located about 10 inches from the throttle body on the cold pipe. BOV's (in my opinion as well as OEM opinions) should be located between the intercooler and TB.

[ispypsi]

s14 sr bov's are mounted under the fuse box off the cold pipe by the throttle body, so what that means is that it ultimately it doesnt matter, as long as its functioning.

i totally understand the "column of air" theory that gets tossed around, but ive driven both ways (before and after IC), and there's no difference. its the butt dyno talking...kinda like "hey i think the car picked up 3hp from blocking off the EGR".

[Import_Ant]

A BOV doesn't neccesarily perform better before >or< after the intercooler, it is simply exposed to more heat when placed before the IC and thus the lifespan of the valve is reduced. That's it. The difference is negligible IMHO but when you are designing a car from scratch like auto manufacturers do, even small nuances tend to be accounted for.

[2_Liter_Turbo]

The reason why you want the BOV near the throttle is because when the throttle closes under boost, all that compressed air wants to go somewhere. So it backtracks towards the turbo. If you have the BOV on the hot pipe, then that back pressure will have fight its way through all the IC piping and the IC itself. This causes the airflow to be all screwed up resulting in compressor surge, and sluggish throttle response. If the BOV is located near the TB, then the air is taken out right after it hits the throttle plate, and re-circulated (in a optimum scenario, or you can vent it) back into the non pressurized side of the intake tract. This will make the flow after the compressor a lot smoother, resulting in better throttle response.

[Import_Ant]

The reason why you want the BOV near the throttle is because when the throttle closes under boost, all that compressed air wants to go somewhere. So it backtracks towards the turbo. If you have the BOV on the hot pipe, then that back pressure will have fight its way through all the IC piping and the IC itself...

you are forgetting that the pressure discrepancy in the hot pipe (under this scenario) will create a vacuum, pulling the pressure toward the BOV.

Take two empty 2-liter pop bottles. blow in one and pop a hole in the *** end of the bottle. do the same w/ the second only pop a hole near the neck. you're going to get the same result.

as far as recirculation goes I agree but it's irrelevant whether you're recirculating from a BOV on the hot pipe or cold pipe because you will still get the same end-result.

/bickering mode

[2_Liter_Turbo]

But why would you want it to have to pull that air through the IC when you can just let it be released near the origin (TB) ? That and the Turbo is begging to build pressure right after the shift. Just makes more sense logically to locate it near the TB. That's why OEM's do it.

[Import_Ant]

But why would you want it to have to pull that air through the IC when you can just let it be released near the origin (TB) ? That and the Turbo is begging to build pressure right after the shift. Just makes more sense logically to locate it near the TB. That's why OEM's do it.

you're thinking of air as something concrete like a stick. you dont have to move the mollecule of air that is located at the throttle body all the way back through the intercooler and out the BOV to reduce pressure, you just have to displace a percentage of the volume of air in the system to reduce overall pressure.

The reason factories place the BOV AFTER the intercooler is because it reduces the heat the bov is subjected to and increases its life span. Seriously.

[2_Liter_Turbo]

I guess then, what is the advantage of it being on the hot pipe? I wouldn't be able to think of any, except that it is "easier" to recirculate it.

I'll still fab up a re-circulation kit from the cold side, when I make my own FMIC setup. Not like I think he's god or anything, but Dave Coleman from SCC wrote an in depth article on why it is better to locate the BOV on the cold pipe rather than the hot pipe. The article made snese to me, so that's what I'll stick to.

[Import_Ant]

there really isnt any advantage other than ease of placement and that's subject to application.

[C-Kwik]

The reason why you want the BOV near the throttle is because when the throttle closes under boost, all that compressed air wants to go somewhere. So it backtracks towards the turbo. If you have the BOV on the hot pipe, then that back pressure will have fight its way through all the IC piping and the IC itself. This causes the airflow to be all screwed up resulting in compressor surge, and sluggish throttle response. If the BOV is located near the TB, then the air is taken out right after it hits the throttle plate, and re-circulated (in a optimum scenario, or you can vent it) back into the non pressurized side of the intake tract. This will make the flow after the compressor a lot smoother, resulting in better throttle response.

You should understad that the BOV does not need to bleed out an huge amount of air. When you close the throttle, the turbine will see very little aiflow. But a turbo does not spool down as fast as surge would occur. The BOV only needs to flow enough air to allow the turbo's airflow through the compressor to remain high enough to prevent surge. It does not actually need to lower the pressure in teh system. Furthermore, the entire column of air would never move backwards through the system. As the turbo will still be pushing air into the piping, most of the air bled out of the BOV will be from the direction of the compressor. If some air were to backtrack, it would be at a relatively slow rate. Air moves based on pressure differentials. And at that, the volume of air that is between the BOV and TB would lose pressure bleeding off whatever air the pressure in this section has vs the what is between the BOV and the turbo and relative to the atmospheric pressure.

While a relatively small concern, if I were to be picky, I'd want the BOV to see actual pressure spikes rather than through an intercooler where the IC might hinder flow a bit. With the relatively small amount o air moving through the system anyway, it would not be a huge concern either way and either location would really suffice in preventing surge.

As far as Dave Coleman's article, I recall reading it. I wish I could find it, but I do recall not walking away from reading it feeling enlightened.