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Old 11-15-2018, 04:47 PM   #1
Sweep
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Default Dump or Recirculation valve?

I've been eyeing up this recirc valve from Forge lately, the 940's been on the back burner for a while but it's back in the limelight.
https://www.forgemotorsport.co.uk/Tu...duct--756.html
It has a HY35 strapped to it, however we have idle issues which I assume is down to not having any sort of recirc valve.

Are there any pros/cons to either dump or recirculation? Does one prefer to work with 2.4 over the other?

Ben.
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Old 11-15-2018, 04:52 PM   #2
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What is currently fitted?

I have no bypass or dump valve of any sort and no idle issues.
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Old 11-15-2018, 05:15 PM   #3
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There was a thread started a while back that said a dump valve shouldn't cause stalling issues on lh2.4, but I'm pretty sure it prefers a recirc valve
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Old 11-15-2018, 05:45 PM   #4
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I have recently had the same issue sweep. I've got an Owen developments 19t and fitted an atmospheric bov where the original recirc goes and it would stall everytime coming up to a junction and struggled to idle. Refitted the stock recirc and the problem instantly went away.
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Old 11-15-2018, 05:47 PM   #5
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I've been following your thread on voc by the way and look forward to seeing the potential of your setup.
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Old 11-15-2018, 07:45 PM   #6
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If your car has an airflow meter you should recirc because the air has been measured.
Dumping measured air will mess with fueling same as an air/vacuum leak.
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Old 11-15-2018, 08:05 PM   #7
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Your car is a much better sleeper if it doesn't make blow off noises. Plus it's better not to lose measured air as mentioned above. I use a Forge valve made as a replacement for Saab. It looks just like the Bosch ones only is metal and will handle higher boost pressures.
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Old 11-15-2018, 08:26 PM   #8
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Search up the many threads already started about this. They explain everything
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Old 11-15-2018, 10:17 PM   #9
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Search up the many threads already started about this. They explain everything
That would be too hard... Don't ya know how it works around here?
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Old 11-16-2018, 07:38 AM   #10
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Quote:
Originally Posted by crogthomas View Post
What is currently fitted?

I have no bypass or dump valve of any sort and no idle issues.
It doesn't have anything fitted currently.
Quote:
Originally Posted by LeedomtoFreedom View Post
There was a thread started a while back that said a dump valve shouldn't cause stalling issues on lh2.4, but I'm pretty sure it prefers a recirc valve
Quote:
Originally Posted by martin84 View Post
I have recently had the same issue sweep. I've got an Owen developments 19t and fitted an atmospheric bov where the original recirc goes and it would stall everytime coming up to a junction and struggled to idle. Refitted the stock recirc and the problem instantly went away.
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I've been following your thread on voc by the way and look forward to seeing the potential of your setup.
Thanks, I'm looking forward to it as well! I think it's the best thing to try, I don't like blow off noises so would prefer a recirc anyway.
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Search up the many threads already started about this. They explain everything
That would be far too easy!
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Old 11-16-2018, 10:03 AM   #11
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Quote:
Originally Posted by Sweep View Post
It doesn't have anything fitted currently.
Then your problem lies elsewhere, don't complicate things by adding a recirculating bypass valve, it's not required for the engine to run or idle.
A rough idle is almost always down to a air leak somewhere. Unless there is something not set up correctly. Was it fine before?
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Old 11-18-2018, 12:44 AM   #12
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I've noticed 3 things that can cause idle roughness on these engines:

1) vacuum leak
2) bad AMM
3) dead in tank fuel pump

If you know your pumps are good and you've tested with a spare AMM, I'd look for vacuum leaks like crogthomas suggested.
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Old 11-18-2018, 02:32 AM   #13
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Then your problem lies elsewhere, don't complicate things by adding a recirculating bypass valve, it's not required for the engine to run or idle.
A rough idle is almost always down to a air leak somewhere. Unless there is something not set up correctly. Was it fine before?
A fair comment, it's not been on the road for 3 years but yes it was fine when I picked it up. I don't currently have any sort of boost control so the little port on the compressor housing isn't connected, could that be an air leak causing it to die?

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I've noticed 3 things that can cause idle roughness on these engines:

1) vacuum leak
2) bad AMM
3) dead in tank fuel pump

If you know your pumps are good and you've tested with a spare AMM, I'd look for vacuum leaks like crogthomas suggested.
I bought the 012 from a member on here under the impression it was a good unit.
Pump is a Walbro 255.
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Old 11-20-2018, 06:35 PM   #14
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If that port isn't being used for boost control it should be plugged. If it is going to be used for boost control it goes to the wastegate actuator.

No connection at all is a large air leak causing a loss of measured air and idle roughness.
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Old 11-21-2018, 10:53 AM   #15
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If that port isn't being used for boost control it should be plugged. If it is going to be used for boost control it goes to the wastegate actuator.

No connection at all is a large air leak causing a loss of measured air and idle roughness.
That's excellent, thanks! I'm on holiday on your side of the pond until December so it'll have to wait.
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Old 11-21-2018, 04:39 PM   #16
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I bought the 012 from a member on here under the impression it was a good unit.
Pump is a Walbro 255.
Assumption, the mother of all F*** ups! Test and KNOW, rather than assume.
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Old 11-22-2018, 12:27 AM   #17
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Assumption, the mother of all F*** ups! Test and KNOW, rather than assume.
Ain't that the truth! Is there a surefire way of testing them?
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Old 11-22-2018, 01:00 PM   #18
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Ain't that the truth! Is there a surefire way of testing them?
The best test I've read of is to compare running specs/performance UNplugged vs. plugged in. BOSCH certainly isn't unique to this breed of vehicle. When there is no difference in operation..... she's dead Jim.
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Old 11-25-2018, 10:59 PM   #19
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A dump valve is always a vacuum leak, its always slightly open while the engine is running. Re-circulation is not, because its after the maf and its not leaking un-metered air. Any Maf (or amm if you prefer) car will not run correctly with a dump style valve on LH 2.4 because of the maf.
Refer to post #6 Dirty Rick, he is correct.
Using no bypass or dump such as crogthomas says he does leads to premature turbo bearing failure, especially if running a decent amount of boost. When letting off the throttle under boost the air pressure backs up in the intercooler tubes, pushing back on your turbos impeller, trying to spin it backwards, its not made for that stress.
Did you hook that port on your wastegate to the actuator yet? Super important...don't even bother with anything else till thats done
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Old 11-27-2018, 06:02 PM   #20
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Using no bypass or dump such as crogthomas says he does leads to premature turbo bearing failure, especially if running a decent amount of boost. When letting off the throttle under boost the air pressure backs up in the intercooler tubes, pushing back on your turbos impeller, trying to spin it backwards, its not made for that stress.
Almost but not quite. Surge won't try to spin the wheel backwards; and even if there is some torque reversal at the wheel it's not the main concern.

Compressor surge essentially creates a rapid oscillating axial thrust load, pulling and pushing the shaft in and out. With a journal bearing turbo that can quickly damage the thrust bearing since it will likely get overloaded with more thrust load than a hydrodynamic film can support. With a ball bearing turbo that has angular contact paths, there is no separate thrust bearing, and they can take a lot more abuse via surge without any real damage.

The reason the wheel and rotor group thrusts in and out in surge is due to the pressure differential from the front of the wheel to the backdisc. You always have a net positive force pushing the wheel out of the turbo on boost, because the cavity behind the wheel "fills up" and reaches close to full boost pressure. The cavity in front of the wheel is the intake tract of course, and will be slightly below atmospheric. So there's always a net force pulling the wheel outward. Hard compressor surge is a pressure oscillation and even some flow reversal, but the main impact is that the static pressure behind the wheel will vary rapidly, which beats the crap out of the thrust bearing (again, in a JB turbo with a separate thrust bearing).

The dorifto guys running no BOV at all and getting away with it are likely also using ball bearing turbos.
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Old 11-28-2018, 04:11 PM   #21
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Are Holsets journal or ball bearing?
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Old 11-29-2018, 11:29 AM   #22
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Quote:
Are Holsets journal or ball bearing?
Mostly journal
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Old Yesterday, 10:29 AM   #23
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Last edited by Thebrick_740turbo; Yesterday at 10:30 AM.. Reason: Read forum wrong
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Old Yesterday, 04:24 PM   #24
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