Should we consider a BOV

[foxracer1]

I have had several people that are decent mechanics yet have 0 experiance with diesels ask how the engine controls its speed. Where the throttle blades are.

[vanagonturbo]

throttle blades eh? :lol:

[Darkness_is_spreading]

Ok so we have gotten some were here,  I'm gonna go with a BOV,  and then control the pressure that leads to that BOV with T fitting off of LDA line.  Have in NO   or NC (Normally open  Normally Closed) and see how that affects the performance......   Plus I get a wicked sound

[gigaz2]

utterly pointless in my view, but, as someone else said: its your wallet.

I would do it if I had the parts around and time to kill, as a joke, like i did this time:

:lol:  :lol:  :lol:  :lol:

[Dr. Diesel]

it's all about the wicked sound. Just like putting a "BOV" on a G60 engine. Utterly useless.
I doubt you'd even get much of a sound, at least, nothing like a gas engine.
Like Libbypapa said, at high RPM, under full boost when you shift, the engine's still at 5500 when you let off the pedal. It's still drawing 300cfm (or what have you) of air, which certainly doesn't pose a restriction to the output of a turbo that has suddenly found itself without any motive force on the exhaust side.
Probably wouldn't even hear it over the diesel clatter.

Maybe you could rig it up so the BOV's outlet pipe runs to a bullhorn carefully duct-taped to the roof. You could even set it up with relays and switches so that the bullhorn only triggers on only above 3000rpm when the throttle is at idle.
Battery life would increase, and you wouldn't spend most of the time amplifying the wind noise buffeting the bullhorn's mic.
Also, I'd probably mount it facing rearwards for better aerodynamics.

[saurkraut]

I totally understand the difference between the gasser need for a BOV and all that. But, the pump slows down to idle after letting off the throttle. Also, with the pump causing the engine to return to idle, doesnt that mean that the valves and pistons slow down?

As we all know, the engine is essentially a pump within itself. So if we slow the pump down then we are processing less air, no? Exhaust and intake alike.


The reason I am interested in this is because I believe I am getting a pretty fair amount of surge after letting off the throttle. Example, 1st gear pull to get to second, then WOT up to 4500 rpm and then let off the throttle. Hence the warbling noise. So if pressure could be vented  somehow that might alleviate stress on the turbo. I plan on using a gt25 on the next engine and I dont it to break the shaft. Especially @ 30+psi.

The engine slows down more slowly that the turbo.  There is allot of rotating mass in the engine, so RPM doesn't plumit.  As a result, I suspect the boost falls faster then engine RPM.  The engine just pumps the 'excess' boost right through.  No harm, no fowl.  If you leave the engine in gear, it slows down even slower.

I'm haveing a hard time correlating 'warble' to a compressor stall.  Compressor stalls tend to make sudden sounds like repeated thump or wump sounds.

I had a K24, that I was running just under 30 PSI, lose a section of a trailing edge of one turbine blade.  It made all kinds of bizzar noises above ten PSI after it crapped the blade piece out of the tail pipe.  I actually heard the piece of blade go rattling down the pipe, so I was able to mark the difference in sounds after word.  It still made boost, but it also made some really strange noise too, and warbling could have been one of them.

You may want to look at your turbine blades and see if everything is OK in there.

Here is the photos of the blade failure:

http://www.vwdiesel.net/phpBB/viewtopic.php?t=14895&highlight=

This is a turbo that lived well above 20 PSI for three years.  It even had new journal and thrust bearings.  The shaft didn't snap, the compressore didn't throw a blade, it never had a compressore stall, and it only lost a small part on one blade.

I suspect the compressore stall problem on the big pick up trucks stems from turbos big enough to injest our tiny turbos, with significant rotating mass, making HUGH boost, on low RPM motors.

Oh, and they have huge "accumulators" (intercoolers) that may not bleed down as fast as out teeny manifolds.

[andy2]

yes, however, take into consideration the size of the turbo on the Dodge vs. the little tiny turbos that we have on the VWs.

Its not really a question of turbo size but rarther Boost pressure.A BOV will only be useful for safe guarding certian turbo(s) when extreme boost pressures of at least 40+ psi are used.

[andy2]

Ok so we have gotten some were here,  I'm gonna go with a BOV,  and then control the pressure that leads to that BOV with T fitting off of LDA line.  Have in NO   or NC (Normally open  Normally Closed) and see how that affects the performance......   Plus I get a wicked sound

A BOV will not affect the performance in any shape or form.

[zukgod1]

Wow for all the knowledge here there sure is allot of naivety.

The BOV would serve a purpose other than just making a cool sound (if you like that) it would allow the boost pressure that is built up in the charge piping a place to go in the event of a sudden peddle lift.

Believe it or not there is a drastic difference in pressure from the exhaust side to the intake side when this happens. Throttle blade or not it's there.
This is the reason turbo bark/ surge occurs and it will eat your turbo in time, experience speaking here not just throwing up on the key board.

The problem is getting a BOV that reacts fast enough to do any good, if it opens to late it's pointless if it doesn't close fast enough once again your defeating the reason for having it. the factory BOV has this problem, but then again it wasn't designed as a BOV it was designed as merely a safeguard against over-boost. Where we don't have throttle plates as well all know it will be difficult to control it accordingly. there may not be enough pressure difference to get it to function as required.

I would like to have one on my system but I'm so tired of throwing parts at the damn thing I just don't see it happening. I'll just be nicer to the peddle and keep driving.

[zukgod1]

The peak boost level does NOT occur after the pedal is lifted, but rather before.  Therefore, how is it proposed that a BOV be actuated in order to routinely release the boost pressure when the accelerator is suddenly lifted?

On a gas engine, the intake pressure increases after the pedal is lifted, and so a BOV can simply be programmed to open when over-pressure occurs.  Not so on a diesel...

Andrew

Exactly, this is a problem.  Where we don't have a throttle plate making the damn thing work is a problematic.
Sure we can probably figure out a way to get it to open at say 25psi but when will it close and what if we are still in the gas (sorta speak) at 25 psi? It opes and we loose all the boost.

[vanagonturbo]

The engine slows down more slowly that the turbo.  

So I read this earlier today and decided to check to see if this is correct. I do not beleive it is. I ran my car at WOT in second gear a few times today and observed that the engine would return to idle and the boost pressure would remain at 6-7psi for about 3 seconds before returning to 0 on the gauge.

So, that in mind, the engine is obviously slowing down faster than the turbo. This test was done only at about 15psi as I didnt have a lot of road and I didnt want to take my eyes off of traffic on the freeway.

What say the group?

[vanagonturbo]

Ok maybe I was not very clear in my posts. I totally agree that there is no need for a BOV on a regular setup.

Mine is not regular. I have not blown any turbos either. I am just looking at this thread and trying to participate with my own worries. My turbo was recently rebuilt and I dont really want to ruin it.

The turbo that I am using is the T3. I have the DV plugged and the wastegate disconnected. I see 25psi of boost regularly. I have an intercooler (albeit, its from an S4 with plastic ends tank but it does a decent job for now). Pump is tweaked (gov mod, fuel screw, boost pin, star wheel, etc).

I would also advocate for a DV over a BOV any day. Screw the noise, Im not concerned with that.

[CoolAirVw]

Wow has this thread taken off.  BOV crowd on the left with knives!  Non-BOV crowd on the right with baseball bats!  Lets have at it!  

ok so what happens then when going from full boost @ 4500 rpm (25PSI) to an idle? Is the engine still processing that much air? No. What happens to all that air? It gets stopped up and pressurizes the intake the wrong way. My car makes a fantastic warbling noise under these conditions, and I too am worried about shaft snappage.

Are you really driving that way?  That seems unusual.  It would seem most people would accelerate through boost then back out at 4500 rpms, but the trans would still be in gear and the RPM's wouldn't drop to idle.  The RPM's would be controlled by the gear you are in, and road speed.  Obviously RPM's would drop gradually as the car slowed.    

Sure if you Race your car up to 4500 then push in the clutch and coast for a while your car will drop back to idle.   Certainly you dont race up to 4500 then push in the clutch, let the car dop to idle, then shift to 2nd, race up to 4500, let the car drop to idle ect, ect.  

What makes boost?   Fuel and RPM.  when you snap that throttle closed, your taking away fuel very fast.  And in most circumstances your road speed, clutch and trans will keep the rpm the same.  Obviously road speed will slowly decrease with removal of throttle.  But they dont drop to idle unless you push the clutch and let it drop to idle.  

What controls air flow?  RPM.  And what controls RPM?  Dont say the throttle!  ROAD SPEED controls RPM! (taking into account gear ratio), That is, if you have a manual, and your clutch isn't slipping.  Your RPM's, and therefore the volume of air you are injesting, will be controlled by your road speed.  

So unless your racing your car up to 4500 then snapping the throttle closed while holding the clutch down or while staying in a lower gear, then I really dont think RPM change is causing a airflow restriction.

[CoolAirVw]

it's all about the wicked sound. Just like putting a "BOV" on a G60 engine. Utterly useless.

Sorry for my ignorance.  A G60 is a supercharged Corrado correct?  

I'm trying to understand why a supercharged car wouldn't need a BOV.  Is it because the boost is made "POST-THROTTLE-PLATE"  So there's not Boost backing up against the throttle plate??

[zukgod1]

Anyone who is snapping their throttles closed on their TD VW engines should be permanently banned from this forum...  

Andrew

I'll second that notion!!!!