Compressor surge, Is it really that harmful ???

[neil_jdmr]

I have read so many conflicting reports of the damage compressor surge can do. some folk saying wear and tear on turbo\'s causing end-float etc.
Other folk saying it causes no problems whatsoever i.e your turbo\'s are under far more stress just spooling up everytime you put you foot down so the stress is next to nothing. Nothing but an excellent bit of marketing etc etc
 
Many tuners use/don\'t use them for many different reasons.
 
Is running without a bov for short periods of time (as in all summer) really gonna cause any problems?

[Timmy]

I would say depends more on the turbo you are runnning. Big turbo\'s seem to take compressor surge quite well. Small turbo\'s not so well. The only real thing you can go on is asking people how long that specific turbo has lasted other people.

[Grizzly]

Has allot to do with what turbo you are running/Power your running/How much abuse you give it and things like that. Don\'t forget the Most Boost your giving it the more Violent the effects.

I had a T04R that was put together by Innovative in the US, i ran that for 2-3 years with no bov as an ever day car, after that time i could honestly say there was little wrong with it.

On the other hand i know people that have had issues, but at the end of the day its an educated risk, that said if i was running big HP i would proberly not think twice about fitting one.

[neil_jdmr]

So from what your saying on a standard twin set-up running standard boost the effects would be minimal right?.
 
But with a big single running plenty o boost a bov is advised
 
 
Correct?

[rx7veilside]

think of the turbo as a propellor and u put air through the front and spin the blades then put the same amount of air thru the back at the same time as cutting the air at the front..quite a shock to the system when u are talking abut the rpm of the blades
bov are a safety device first and foremost..forget the sound all road going turbos have either a bov or relief valve for one reason longevity of the turbo
if u want ur turbo to last fit a bov if u want to take a chance then dont its that simple
forget the comments about ive not had one for this and that each person makes their own choice sometimes without really knowing what the vave does
and of course the rally cars dont run them thats because they dont wory as the team strip and rebuid the parts regular ie after every race and dont have to pay for the things

[Timmy]

Big turbos with lots of boost even with a dv you stall get compressor surge because it can\'t expell enough boost quick enough.
Any way compressor stall on stock twins probably causes more damage than say a t04r at 1bar with no dv. It\'s more to do with the bearings of the turbo.

[Grizzly]

So from what your saying on a standard twin set-up running standard boost the effects would be minimal right?.

TBH i\'ve never seen it done with Twins.

[Ricco_04]

It\'s more to do with the bearings of the turbo.

Yup, I have always been lead to believe its the bearings.  Stock turbos dont have a 360deg bearing. You could run without a bov but I wouldn\'t want to do so myself.

[neil_jdmr]

so no-one with standard twins has ever ran without a bov, I honestly cannot see why whether the compressor blades run forwards or backwards would decrease the life of the bearings. Surely like all bearings they are designed to run both ways and only the blades are slanted to deliver air in any one direction.
My other point would be i understand that holding pressure in a system would be harmful but even without a bov the air would pass through the blades and out of the exhaust hence no build up in pressure.
 
Has anyone any real experience of damage that not having a bov causes or the usual horror stories just being repeated?
 
Before anyone jumps in to give me an ear bashing i am only throwing in these questions as it helps me learn more. i am not planning on blanking my bov off personally but am keen to know the TRUE affects this has. From my experience in industry the only reason bov/prv are used is to release when a set pressure is exceeeded and has nothing to do with compressor life preservation.
 
Again iam only asking questions and not looking for a lashing

[Grizzly]

Yup, I have always been lead to believe its the bearings.  Stock turbos dont have a 360deg bearing. You could run without a bov but I wouldn\'t want to do so myself.

Actually its more to do with Shaft failure (Imagen the amount of Exhaust gases does not change but on the other side of the turbo the Throttles are now shut,simply the pressure will build on the colds side until both sides are the same then the compressor stalls, all this happens in hundredths of second) the bearings will let go if you run higher boost levels, 360\'s help with that, the surge is renown for snapping shafts. Thats why the bigger turbo\'s handle it better (T series turbo\'s hard thicker shafts which made them stronger but also heavier)

If that made sense...

[rx7veilside]

the dump valve has nothing to do with releasing pressure when it reaches a certain point
the wastegate controls the pressure and stops u boosting to silly levels in excess of your mapping
the bov will stay shut(failing a fault)until u lift off pressure by lifting the pedal
your engine will explode long before the d/valve will release pressure it is a simple device on boost the valve is forced shut and will stay shut until u lift off the pressure at which point the valve will vent the air either to atmo or recirc thru the intake

[Grizzly]

Has anyone any real experience of damage that not having a bov causes or the usual horror stories just being repeated?
 

Well not me personally but i\'ve seen the damaged caused on 5 turbo\'s etc when running high boost with no BOV. I can tell you 100% it can be catastrophic damage (the main one is Shaft failure or bent shafts  but i\'ve seen bent Fins on Wheels and even blades missing dues to surge or so i was told by the Turbo people) tbh i would not be at all suprised if the bearing may need changing after a Shaft failure?

mazda didn\'t fit a BOV to the stock car for no reason, everything was put through R&D

[neil_jdmr]

the dump valve has nothing to do with releasing pressure when it reaches a certain point
the wastegate controls the pressure and stops u boosting to silly levels in excess of your mapping
the bov will stay shut(failing a fault)until u lift off pressure by lifting the pedal
your engine will explode long before the d/valve will release pressure it is a simple device on boost the valve is forced shut and will stay shut until u lift off the pressure at which point the valve will vent the air either to atmo or recirc thru the intake

Yes mate
 
I understand that but the bov is there to release the pressure left in your system once you lift off and if it isnt released to atmos/re-circ it is released back through the blades and out the exhaust.
 
I think im getting it now,
 
So because once ive lifted off milliseconds before the bov opens the turbo is still spinning ( over spinning effectively) and the pressure build up between the turbo and the still closed bov would stall the compressor until it forces it backwards hence forcing it one way then the other. Is it the fact that the pressure changing the direction of the compressor that causes problems???
 
If so surely when driving off boost before the compressor gets spinning the exhaust is drawing air turning the compressor backward anyway???

[BlitzBoy]

there is a big thread on ausrotary with Pros and Cons. Been discussed many times on here.
On standard twins keep the valves as MAzda intended as the turbos and shafts on twins are small, if you run a big shaft single turbo no point, Id rather keep the performance benefit of running without bov, plus I have seen no damage on my turbo or others that run without on big singles.
If ya scared of damage then run a BOV

[BlitzBoy]

So because once ive lifted off milliseconds before the bov opens the turbo is still spinning ( over spinning effectively) and the pressure build up between the turbo and the still closed bov would stall the compressor until it forces it backwards hence forcing it one way then the other.?

The compressor wheel does NOT STOP SPINNING or Stall.
Exhaust gas is still turning the Turbine BLade!! it will not rotate in the other direction!

The other man use of the recirc valves was to do with emissions