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Old 04-17-2010, 02:14 AM   #1
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Default recirc. BOV, hot or cold side?

I'm sure it's been discussed here as it has on every DSM/SRT forum, however, I thought I'd bring it up.

I'm currently plotting my over the top intercooler set up for my 1.6 - hoarding parts, convincing family members that Dad really needs that tig welder for his birthday , etc.

The one detail I've been back and forth on is where to mount my recirc. BOV (I like silence). It seems miata tradition is to mount it to the cool side near the TB which seems to make some sense - TB closes, pipes pressurize, air is evacuated at the point of pressure concentration. There's nothing really preventing me from running this set up except I'd prefer to not route 2-3' of 1" tubing back to the intake. Then I started questioning whether it really needed to be near the TB at all. It seems that the delay (if any) in pressure onset near the TB vs. the hot side piping would be pretty negligible and releasing the pressure anywhere in the piping would still prevent the compressor wheel from 'stalling'. By running it on the hot side it would allow me run a much shorter return line there by avoiding the cluster **** caused by a relocated radiator with stock fans.

I've noticed in a few forum searches that there's a couple members who have gone this route - perhaps they can chime in.

-Zach
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Old 04-17-2010, 03:07 AM   #2
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The possible downside I see with putting it on the hot side is running the risk that the diverting line won't be able to contain all the excess pressurized air.
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Old 04-17-2010, 11:51 AM   #3
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The closer to the tb it is the less the flow of air is reversed. Lets say you put it on the hot side then after you close the tb then all air has to slam to halt and gets swirled around, and when you get back on the throttle the air has to straighten out and start moving forward again. However if you put the bov near the tb then all air continues to move forward and when you get on the throttle the air is already moving in the correct direction.
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Old 04-17-2010, 04:55 PM   #4
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Quote:
Originally Posted by ZNuT View Post
The closer to the tb it is the less the flow of air is reversed. Lets say you put it on the hot side then after you close the tb then all air has to slam to halt and gets swirled around, and when you get back on the throttle the air has to straighten out and start moving forward again. However if you put the bov near the tb then all air continues to move forward and when you get on the throttle the air is already moving in the correct direction.
This makes sense - maintaining direction of flow.

Perhaps I'll just slap a filter on the BOV and call it a day.

-zach
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Old 04-17-2010, 04:59 PM   #5
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This makes sense - maintaining direction of flow.

Perhaps I'll just slap a filter on the BOV and call it a day.

-zach
If you are still running the stock ecu or any MAF setup then you car will go rich when you shift and will most likely bog. If running MAP setup then no worries.

Also you don't need a filter on a BOV since the air only goes out. Well expect if you use some stock recirculating valves (BOV's).

Last edited by ZNuT; 04-17-2010 at 06:14 PM.
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Old 04-17-2010, 05:36 PM   #6
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If you are still running the stock ecu or any MAF setup then you car will go rich when you shift and will most likely bog. If running MAP setup then no worries.
truth,

earlier when i ran my setup on stock ecu with VTA bov everytime i shifted it bogged a bit and shifting was shitty as well because of the indefinite rpm drop
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Old 04-17-2010, 07:07 PM   #7
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Originally Posted by ZNuT View Post
If you are still running the stock ecu or any MAF setup then you car will go rich when you shift and will most likely bog. If running MAP setup then no worries.

Also you don't need a filter on a BOV since the air only goes out. Well expect if you use some stock recirculating valves (BOV's).
running MS so it's not an issue.

As for the filter, I realize there's positive pressure so the engine should ingest anything, however, there's nothing stopping dirt ingress at rest (I live in a dust bowel) and sliding seals + particulates = fail.

-Zach
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Old 04-17-2010, 09:13 PM   #8
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Quote:
Originally Posted by ZNuT View Post
The closer to the tb it is the less the flow of air is reversed. Lets say you put it on the hot side then after you close the tb then all air has to slam to halt and gets swirled around, and when you get back on the throttle the air has to straighten out and start moving forward again. However if you put the bov near the tb then all air continues to move forward and when you get on the throttle the air is already moving in the correct direction.
...and the logic for putting it on the hot-side closer to the turbo is to let the turbo more quickly dump pressure while it holds more turbine speed. Is there more to gain by maintaining the inertia of the air or more to gain from letting the turbo freewheel? I'm certain that you won't tell a difference either way and it doesn't matter.

This was recently discussed in another thread and it makes no difference really.
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Old 04-17-2010, 11:36 PM   #9
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...and the logic for putting it on the hot-side closer to the turbo is to let the turbo more quickly dump pressure while it holds more turbine speed. Is there more to gain by maintaining the inertia of the air or more to gain from letting the turbo freewheel? I'm certain that you won't tell a difference either way and it doesn't matter.

This was recently discussed in another thread and it makes no difference really.
+1 I would rather keep the turbo spooled.
+1 It really does not matter anyway. Whatever is easier to install.
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Old 04-19-2010, 12:58 PM   #10
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Old 04-20-2010, 01:24 AM   #11
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Ran mine hot side...I will also recirc right in front of inlet. My understanding is it's better for the turbo the closer it is to it...but at non-radically built motor boost (ie 12-15ish psi) there is no way to notice it all. Mount it in the cleanest place for your setup and be happy.
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