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Deleting Manifold Blow off Valve?
by
Bugsy_malone 666
on 19 Mar, 2013 01:57
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Well I am wondering about the BOV on my 1.6TD, basically the other day when I was testing (before taking to bits) I was giving my van some death up hill and it basically was blowing off the pressure and ending up with a load of black smoke.
So while its currently in bits and I am doing some stuff to the engine (lifters and timing mainly) I wondered about the BOV, so I took it out to have a look. Seemed to move fairly easy pushing my thumb on it, so I wondered if it was working at all! That then made me think, do you really need a BOV on a diesel?
Have many people deleted the BOV?
What alternatives are there?
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#1
by
vanbcguy
on 19 Mar, 2013 06:00
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I just blocked the hose itself. There are a few ways to disable the valve, or you can buy a block off plate.
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#2
by
spencebm
on 19 Mar, 2013 06:26
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don't need it at all. It is just a back up for wastegate failure. weld that thing shut or buy a block off!
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#3
by
damac
on 19 Mar, 2013 11:28
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I have been pounding my rabbit this last month since I brought it back to life and have been watching the boost gage.
Stock setup, blowoff valve installed.
I am not seeing the gage drop off when floored like people mention?
I see it hitting like 12 something and just staying pegged as I rev the car out on hills, etc.
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#4
by
R.O.R-2.0
on 19 Mar, 2013 11:39
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I have been pounding my rabbit this last month since I brought it back to life and have been watching the boost gage.
Stock setup, blowoff valve installed.
I am not seeing the gage drop off when floored like people mention?
I see it hitting like 12 something and just staying pegged as I rev the car out on hills, etc.
the valve opens @ 12psi..
block it with a wine cork, and go for another run..
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#5
by
81 vw pu
on 19 Mar, 2013 14:33
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#6
by
R.O.R-2.0
on 19 Mar, 2013 14:47
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heres what i did to get rid of the overboost valve..
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#7
by
Bugsy_malone 666
on 19 Mar, 2013 16:33
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heres what i did to get rid of the overboost valve..
Lol, twin plenum manifold I presume? Bit extreme to just block it off lol!
I think the idea of essentially corking it isnt a bad one. If my turbo is boosting over 12psi and holding open, I am certainly not getting boost to push the van up hill! (which presumably means more fuel than boost so runs hotter and potential for piston cooking as opposed to clean boost?)
I think I have a piece of pipe the right size to clamp onto it (it just vents into the air at the minute).
Alternatively I did wonder about a normal BOV from something else. The petrol ones are connected just before the throttle body so when you let of the throttle and the boost suddenly builds up at the throttle butterfly the BOV opens, which is normally adjustable. I figured maybe I could fit the random petrol BOV to the vw one, then linked the 3-4mm pressure feed to the same pipe that does the fuel advance, when pressure reaches 25psi, if the wastegate stops working it will blow off at a preset pressure above 12psi
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#8
by
JamesT
on 19 Mar, 2013 16:57
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BOV on gas motors prevent boost spikes and turbo-bark when quickly lift off the throttle. Because a diesel has no throttle plate, there is no risk of this happening. I'm convinced VW was afraid the waste-gate wouldn't be big enough to fully divert the flow, so they installed it as a precaution, and nothing more. My AAZ manifold doesn't even have a boss cast in it for one, so they finally figured it was redundant.
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#9
by
libbydiesel
on 19 Mar, 2013 17:02
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Napa sells various size expansion plugs that have a rubber donut, two metal washers to squish it and a bolt running through. The 1-1/2" size works well. I've also unscrewed the set screw, dropped in a small bolt and screwed the set screw back in so that the valve is held positively closed.
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#10
by
bajacalal
on 19 Mar, 2013 19:55
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I've seen boost leaks caused by the o-ring which sits under the blow off valve, so if you're having issues, simply plugging the hose or preventing the valve from opening may not solve them.
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#11
by
Bugsy_malone 666
on 20 Mar, 2013 01:04
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BOV on gas motors prevent boost spikes and turbo-bark when quickly lift off the throttle. Because a diesel has no throttle plate, there is no risk of this happening. I'm convinced VW was afraid the waste-gate wouldn't be big enough to fully divert the flow, so they installed it as a precaution, and nothing more. My AAZ manifold doesn't even have a boss cast in it for one, so they finally figured it was redundant.
Yep thats what I was trying to say, however the way the actual BOV works would be the same on anything forced induction, so if you had a supercharged gas motor the BOV would open when you drop off the throttle because of the boost surge and may also remain slightly open on idle if you have a fair amount of boost from the charger - I recall hearing one run a bit like this on a Big V8 VW Type3 Fastback used for Drag Racing.
What I was getting at is its a boost sensitive device so if there is too much pressure it would open, regardless of the application it was fitted too. So in the situation of it being fitted to a diesel and connecting it to manifold pressure feedback(the little hose that also feeds the fuel pump fuel advance), it should start opening when it hits a predfined pressure which can be adjusted.
I think i'll have a bit more of a read up on BOV and look to get a pressure gauge installed+EGT gauge.
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#12
by
RabbitJockey
on 20 Mar, 2013 06:33
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BOV on gas motors prevent boost spikes and turbo-bark when quickly lift off the throttle. Because a diesel has no throttle plate, there is no risk of this happening. I'm convinced VW was afraid the waste-gate wouldn't be big enough to fully divert the flow, so they installed it as a precaution, and nothing more. My AAZ manifold doesn't even have a boss cast in it for one, so they finally figured it was redundant.
it is actually still possible but i think only with a large turbo, in our diesels when u let off the pedal there is no longer any fuel creating heat and drive pressure on the exhaust side of the turbo, so if the pressure left in the intake manifold and piping is not consumed quick enough by the engine, air and reverse through the turbo and cause bark/surge, but like i said i think this would only really happen with a large turbo and lots of boost, but it is definitely possible. not a concern for any of us really tho.
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#13
by
libbydiesel
on 20 Mar, 2013 08:10
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I think turbo bark and surge are two different things. I believe bark noise is generated by the turbine.
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#14
by
libbydiesel
on 20 Mar, 2013 08:12
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This guy used one of the Napa plugs I was talking about or similar.
