BOV before IC or after?
10-26-2010, 08:06 PM
#1
BOV before IC or after?
For those with SCers and an IC, what are your thoughts on the location of the BOV?
Ever since I put on the IC, Ive always had the BOV right after it in the fender area. I recently decided to relocate it to the opposite side in between the blowers outlet and the IC inlet.
I cant say that Ive noticed much of a difference, the car "seems" to have much better throttle response in the lower RPMS but may just be in my head. One thing is for sure, its quite a bit louder now.
Ever since I put on the IC, Ive always had the BOV right after it in the fender area. I recently decided to relocate it to the opposite side in between the blowers outlet and the IC inlet.
I cant say that Ive noticed much of a difference, the car "seems" to have much better throttle response in the lower RPMS but may just be in my head. One thing is for sure, its quite a bit louder now.
10-26-2010, 09:27 PM
#2
Well, I would imagine that venting the air pre-IC would let the IC stay cooler for longer periods, since the air (which gets heated by the SC) wouldn't ever reach the IC. So your intercooler stays more efficient for longer periods. Not to mention the volume of basically pre-pressurized air would be greater (think of a CAI on a NA maxima only with ram air). As far as sound, I would imagine that it has to do with the volume of air being blocked by the TB plate being much larger with the distance being greater from the TB. One of the reasons why most people recommend placing a BOV as close to the TB as possible is to minimize reversion and compressor surge. SO the more air venting from the BOV, the "louder" it gets.
Now I know where I will be putting my BOV when I put in my intercooler.
Now I know where I will be putting my BOV when I put in my intercooler.
Last edited by Mad-MAX_SE; 10-26-2010 at 09:58 PM. Reason: clarification
10-27-2010, 12:24 AM
#4
In my opinion, the best location is before the IC. I have measured boost from different locations and learned that before the IC when you let off there is a spike in boost before the air vents out the BOV. My logic tells me that its due to the pressure drop in the IC. There is always more pressure before the IC than after (unless you have invested $$$$ in a good IC, even then pure physics, there is resistance). So with that said, I recommend before IC. In my case it is more significant, having like 10 feet of charge piping before the IC. The important part is having a BOV that vents really well, I am happy with the 50mm Tial.
10-27-2010, 09:01 AM
#5
Well, I would imagine that venting the air pre-IC would let the IC stay cooler for longer periods, since the air (which gets heated by the SC) wouldn't ever reach the IC. So your intercooler stays more efficient for longer periods. Not to mention the volume of basically pre-pressurized air would be greater (think of a CAI on a NA maxima only with ram air). As far as sound, I would imagine that it has to do with the volume of air being blocked by the TB plate being much larger with the distance being greater from the TB. One of the reasons why most people recommend placing a BOV as close to the TB as possible is to minimize reversion and compressor surge. SO the more air venting from the BOV, the "louder" it gets.
Now I know where I will be putting my BOV when I put in my intercooler.
Now I know where I will be putting my BOV when I put in my intercooler.
The BOV isnt louder when releasing boost under a load, just louder as its venting when cruising.
Ive always heard that too which is why I had it after the IC originally, but most of the time it was refering to TC applications.
In my opinion, the best location is before the IC. I have measured boost from different locations and learned that before the IC when you let off there is a spike in boost before the air vents out the BOV. My logic tells me that its due to the pressure drop in the IC. There is always more pressure before the IC than after (unless you have invested $$$$ in a good IC, even then pure physics, there is resistance). So with that said, I recommend before IC. In my case it is more significant, having like 10 feet of charge piping before the IC. The important part is having a BOV that vents really well, I am happy with the 50mm Tial.
The car really does seem to have a sharper throttle response. Before, when cruising under 3k and suddenly punching it the car would have some hesitation. Would never do it going WOT from 1k and up. I tried to have them eliminate it when I was getting tuned and some was but I was told the Emanage couldnt respond fast enough to get rid of it 100%.
Now with the BOV relocated, its almost completly gone.
My BOV does vent well, its the Vortech Mondo. I originally had the Tial but would get compressor surge with it and couldntget rid of it. Tried swapping springs but all that did was keep it fromventing completely.
Since it wasnt fully adjustable I sold it for one that was.
Last edited by Flava_24/7; 10-27-2010 at 09:04 AM.
11-09-2010, 04:49 AM
#7
You should mount your BOV as close to the throttle plate as possible.
Think about what your "blow-off valve" does: turbocharged air is being rammed into the intake manifold at 4000 fps, the turbo wheels are spinning at 12,000+ rpm, and when you shift, if you let off the throttle, the throttle plate closes, and suddenly all that moving air has nowhere to go. The "blow-off valve" blows that air to atmosphere (or in a metered system, theoretically, you should "bypass" that air back into the tract pre-turbo).
So it backs up along the entire intake tract, and tries to stop the comp/exh wheel assembly in a nano-second.
This is bad. I've seen turbos fail when the wheels are stopped in the blink of an eye, but that little nut holding the compressor wheel on keeps-a-spinning, backs off, and gets ingested by the compressor shortly before the entire thing grenades. Ever heard an improperly bov'd turbo "chug" between gears? It's that afore-mentioned air charge trying to halt the rotation of the compressor assembly, but not quite being able to, so the assembly goes from residual rotation and boost-making rpm to below the threshhold, repeatedly. Ouch.
The spike in boost pressure pre-IC you guys are seeing is all that air backtracking from the TB through the piping, through the IC, before it's able to be vented. The IC is too large a heatsoak to be affected by split-second changes in aircharge or temperature passing through it. It's not going to get hotter by BOV placement after it.
Think about what your "blow-off valve" does: turbocharged air is being rammed into the intake manifold at 4000 fps, the turbo wheels are spinning at 12,000+ rpm, and when you shift, if you let off the throttle, the throttle plate closes, and suddenly all that moving air has nowhere to go. The "blow-off valve" blows that air to atmosphere (or in a metered system, theoretically, you should "bypass" that air back into the tract pre-turbo).
So it backs up along the entire intake tract, and tries to stop the comp/exh wheel assembly in a nano-second.
This is bad. I've seen turbos fail when the wheels are stopped in the blink of an eye, but that little nut holding the compressor wheel on keeps-a-spinning, backs off, and gets ingested by the compressor shortly before the entire thing grenades. Ever heard an improperly bov'd turbo "chug" between gears? It's that afore-mentioned air charge trying to halt the rotation of the compressor assembly, but not quite being able to, so the assembly goes from residual rotation and boost-making rpm to below the threshhold, repeatedly. Ouch.
The spike in boost pressure pre-IC you guys are seeing is all that air backtracking from the TB through the piping, through the IC, before it's able to be vented. The IC is too large a heatsoak to be affected by split-second changes in aircharge or temperature passing through it. It's not going to get hotter by BOV placement after it.
11-09-2010, 04:56 AM
#8
You should mount your BOV as close to the throttle plate as possible.
Think about what your "blow-off valve" does: turbocharged air is being rammed into the intake manifold at 4000 fps, the turbo wheels are spinning at 12,000+ rpm, and when you shift, if you let off the throttle, the throttle plate closes, and suddenly all that moving air has nowhere to go. The "blow-off valve" blows that air to atmosphere (or in a metered system, theoretically, you should "bypass" that air back into the tract pre-turbo).
So it backs up along the entire intake tract, and tries to stop the comp/exh wheel assembly in a nano-second.
This is bad. I've seen turbos fail when the wheels are stopped in the blink of an eye, but that little nut holding the compressor wheel on keeps-a-spinning, backs off, and gets ingested by the compressor shortly before the entire thing grenades. Ever heard an improperly bov'd turbo "chug" between gears? It's that afore-mentioned air charge trying to halt the rotation of the compressor assembly, but not quite being able to, so the assembly goes from residual rotation and boost-making rpm to below the threshhold, repeatedly. Ouch.
The spike in boost pressure pre-IC you guys are seeing is all that air backtracking from the TB through the piping, through the IC, before it's able to be vented. The IC is too large a heatsoak to be affected by split-second changes in aircharge or temperature passing through it. It's not going to get hotter by BOV placement after it.
Think about what your "blow-off valve" does: turbocharged air is being rammed into the intake manifold at 4000 fps, the turbo wheels are spinning at 12,000+ rpm, and when you shift, if you let off the throttle, the throttle plate closes, and suddenly all that moving air has nowhere to go. The "blow-off valve" blows that air to atmosphere (or in a metered system, theoretically, you should "bypass" that air back into the tract pre-turbo).
So it backs up along the entire intake tract, and tries to stop the comp/exh wheel assembly in a nano-second.
This is bad. I've seen turbos fail when the wheels are stopped in the blink of an eye, but that little nut holding the compressor wheel on keeps-a-spinning, backs off, and gets ingested by the compressor shortly before the entire thing grenades. Ever heard an improperly bov'd turbo "chug" between gears? It's that afore-mentioned air charge trying to halt the rotation of the compressor assembly, but not quite being able to, so the assembly goes from residual rotation and boost-making rpm to below the threshhold, repeatedly. Ouch.
The spike in boost pressure pre-IC you guys are seeing is all that air backtracking from the TB through the piping, through the IC, before it's able to be vented. The IC is too large a heatsoak to be affected by split-second changes in aircharge or temperature passing through it. It's not going to get hotter by BOV placement after it.
The SCer is always makeing boost, so if its after the IC then charged air does make its way inot the IC even it if doesnt make its way into the TB.
By placing it before the IC, some charged air still makes it through but no where near as much.
11-09-2010, 08:49 AM
#9
My thread was in regards to a SCer, not a TC.
The SCer is always makeing boost, so if its after the IC then charged air does make its way inot the IC even it if doesnt make its way into the TB.
By placing it before the IC, some charged air still makes it through but no where near as much.
The SCer is always makeing boost, so if its after the IC then charged air does make its way inot the IC even it if doesnt make its way into the TB.
By placing it before the IC, some charged air still makes it through but no where near as much.
... I soooo didn't even see that.....my bad...
Still, I'm not 100% ok with some of what you're saying, tho, Flav, as it doesn't seem to make perfect sense, but I also don't know enough about SC'ers to say otherwise, so I'll butt out now
11-09-2010, 10:07 AM
#10
I thought the very samething and had mine before the IC. It ended up wearing out my throttle body within a few months and it starting leaking causing idle problems. So I moved it much closer to the throttle body after the IC and never had a problem. Keep in mind I went really high on boost with this setup and had no problems in this department.
11-09-2010, 10:16 AM
#11
I thought the very samething and had mine before the IC. It ended up wearing out my throttle body within a few months and it starting leaking causing idle problems. So I moved it much closer to the throttle body after the IC and never had a problem. Keep in mind I went really high on boost with this setup and had no problems in this department.
How much boost did you make?
11-09-2010, 10:27 AM
#12
Regarding boost. I was running a 1.725” pulley.
11-09-2010, 11:46 AM
#13
The throttle body is not designed to have positive pressure against it. If the BOV not in front of the throttle body then the pressure remains. At least this is the best I could figure so I moved it from between the SC and the IC to 6-8 inches from the throttle body.
Regarding boost. I was running a 1.725” pulley.
Regarding boost. I was running a 1.725” pulley.
1.725??? Thats crazy small. Im surprised the blower didnt crap out, thats some major over spinnage.
Where you running the normal V2 blower?
11-09-2010, 01:57 PM
#14
Yup, started breaking the flex plate and that was when I started demodding the car and selling off parts. Shatter 2 flexplates in 45 days. Ran out of waqys to keep the power to the wheels.
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