What better way is there to find out other than real world conditions?

 

I guess over 6 years now is not enough proof?

 

6 years... How many miles though for some here that could be 2k miles?

 

I honestly don't think the "he did it for xx years" is proof enough for me. Everyone's setup is different. I mean, Busted7's car has been running 500whp @ 20psi with no AI on pump gas for many years, does that mean everyone can/should do it without problems? No!

I've had a compressor nut back off due to a disconnected BOV, plain and simple. This tells me that the spike in intake charge is putting some amount of force on the compressor wheel. And BTW, I am the one who built the turbo, so you can call me whatever you want, but this has been my experience. At the same time, I think that the spike in pressure between the compressor wheel and throttle plates will be much more of an issue as the turbo becomes larger, due to increased inertia and air flow.

It would be nice to see some testing on the subject, but I don't really see it happening in the near future. It seems to me all the references made to Rally cars and the like don't really apply, as rally cars run anti-lag that causes turbine wheels to deteriorate quickly, so obviously longevity isn't a crucial factor.

 

Trots*88TII-AE*, having a disconnected BOV is the opposite of having no BOV at all. By having it disconnected, the BOV will be open under boost causing a massive boost leak which in turn would cause the turbo to overspin and is the reason your nut backed out. The boost line to the BOV is what keeps the BOV closed under boost and opens it with a pressure differential between the intake and the IC charge.

thewird

 

You're right, my bad. It was a while ago and I had forgot, but the BOV was actually connected to the outlet on the compressor cover. Either way, it was not leaking, but was not relieving boost pressure. I had switched the pressure source and wasn't thinking.

 

Here’s my thought process.
Let’s start at the top level.

Will there be pressurized air in the intake system when the throttle closes? Yes

Is it possible for a throttle to fail? Yes (springs fatigue, debris, wear, thermal shock causing interference ect)

Can pressurized air bypassing the throttle accelerate and engine? Yes

Has this failure ever occurred? Yes (It’s know to happen, l will fully describe my situation once I have access to my compressor maps)

At this point we have a “possible” unintended acceleration so it’s a severity of 10. Remember an unintended change in the rate of deceleration/acceleration is considered a 10 (Toyota Prius regeneration brakes)
Here’s a list of 10’s from AIAG
“Dangerous to Service/Assemble
Unintended vehicle motion
Clutch release linkage failure
Engine cranks with transmission in gear
Vehicle motion in the wrong direction
Unintended vehicle acceleration
Exposure to high voltage
Regulatory Non-Compliance
Noise levels above (SAE J366, ISO 362)
EMC levels above regulation limits

So what about the history? Because the failure is a 10 (dangerous) the history does not matter. Just because people use heroin every day without dying does not mean you can.

Most campanies use the rule

“all failure modes with a Severity of 9 or 10 (safety related) must have corrective actions”

So at this point I look for corrective actions. Here’s my list
Air diversion (BOV, POV)
Fuel cut (requires TPS and air flow inputs, super lean deceleration is not Ideal IMO)
Ignition cut (requires TPS and air flow inputs, can cause overheating exhaust do to late burning fuel)
Wastegate (must be designed to do open on deceleration, most wastegate systems to not react fast enough)
Of these items I prefer BOV. I would not run without one of the above.

In the end it really depends on your system. If the stock fc or fd has the right logic in the ecu then go for it (I do not know I've always been haltech). If you run a map sensor only and you have not tuned for the lack of a BOV beware IMO.

Again I'm not knocking those who do this right, it's just not for me.

 

That doesn't always apply. The typical style with diaphragm chamber(s), spring, and poppet valve usually have enough spring tension to keep the valve from leaking under boost without any kind of boost signal line. There is more than one design out there though so you can't make overgeneralizations.

 

It works the same as a wastegate. After X boost it will open. For example on a Tial BOV you have a choice between 7,9,11,12 psi springs. Couldn't find the spring rate for Greddy's standard and stiff springs but should be similar range. The whole point of the springs are so the BOV stays closed at idle otherwise it would open due to the vacuum at idle. Of course they're are new design BOV's like the synapse but the principle is still the same, they require an external boost source to stay shut past X boost.

thewird

 

i am part of the no bov fan club. compressor surge sounds really awesome on greddy mitsu turbos!

 

Oh interesting. What turbo was this btw?

thewird

 

So here's my map. I'm not near the surge line especially at high RPM were my issue occurred. (See circle) I was running a T04E 57 trim with a 1 A/R turbine housing.




I had the same throttle body and fuel setup on my supercharger and NA setup with no issues. I switch to turbo and the engine would "surged". I would let off the gas and it would rev up for a split second. I adjusted my BOV to the light side and it fixed the issue. Later I figured out my secondary throttle plates were not fully closing every time. I switch to a Lokar throttle cable, new return springs, and adjusted the BOV again and the issue is gone.

 

^

 

lol

 

Is this the case? I wasn't paying attention when I put my setup back together and forgot to put that vacuum line on my bov and I had the compressor surge sound. Granted it wasn't tuned all the way so I wasn't really going over 5 psi and never really WOT.

EDIT: Was running Greddy Type S bov with stock spring.

 

^ The Greddy Type S has adjustable spring preload (the "hard" and "soft" adjustment). It is an allen bolt on the top with a locknut. The BOV will not open under boost unless the spring is overwhelmed. I can tell you that for sure because I drove around for a few thousand miles with my Greddy Type S accidentally hooked up to basically nothing, just atmospheric pressure (it was the port air passageway on the ACV flange).

Cap off your BOV line and pressure test your intake tract to see what I mean. If the BOV is adjusted tight enough it still won't leak.

Yes. And X boost could be determined by the spring pressure itself or adjusted preload. If that's stiff enough, it won't leak whether you have a pressure source hooked to it or not.

 

How much could the preload affect the trigger boost for it to crack? Most people don't run the stiff springs and I don't think you could double the load it can take with the preload screw? If I wasn't out of the country I would indeed test it, boo.

thewird

 

I think you misunderstood me. I was just getting at that my bov doesn't open with no vacuum source hooked up to it, which contradicted what thewird said (bov opens with no vacuum line hooked to it and creates a huge boost leak). I wasn't paying attention and never hooked up a source to it and it never opened under 5 psi of boost. With vacuum it opens up 100% fine. Though I think I do need to tighten the allen bolt since between shifts for just daily driving (not fast shifting) the bov will somewhat linger open for a little bit longer than it did with my old small turbo.

 

You'd be surprised. Cap off the hose(s) to the BOV. Do a boost leak pressure test where you connect the tester to the turbo inlet. Have someone slowly increase the pressure through the system with the regulator. Start messing with the adjuster and you'll see what I mean. On adjustable BOV's I like to use this pressure testing method to help me set the preload.

Now here's something else interesting. Rig up some plumbing fittings (hose, reducer, etc) and test the factory FD air bypass valve. Leave the top nipple on it open. Good luck making that thing leak if you pressurize it from the correct side. I think I got it to hold 60psi before it blew my makeshift tester off. The factory valve appears to be a pull-type.

 

Logic fail.

If the BOV is hooked up in the conventional fashion diaphragm reference post throttle and the throttle sticks (assuming you are not running drive by wire, using pedal as "requested load delivery"), the BOV will not open, the only way that it can work as a partial safety device (down to atmospheric pressure only so still have engine producing torque) is if the system is Drive by wire AND you run a solenoid on the BOV reference line that ports to atmosphere with a very weak BOV spring.


I think it is Hilarious that all of the endurance motorsport setups through the 80s running plain bearing turbos at high boost, didn't run BOVs, yet so many idiots pander to all the bullshit marketing. Do you think when some of the competition was using antilag and heaps of fuel in doing so that if teams could improve response on gear changes by dumping compressed air that would otherwise provide the engine torque & exhaust energy to keep the turbo pushing target boost in the next gear they wouldn't use a device that weighed less than the fuel some of their competitors were dumping during a race while heat loading everying in the engine bay??

I have seen logs from teams testing this stuff, on fast gear changes the non bov cars come back on harder, for obvious reasons, they can even kick back off as boost levels they would not otherwise be able to reach at those revs.

They are on most efi turbo cars because they run Mass flow meters which get disturbed without them if the ecu does not go into open loop off throttle.

For everyone with a MAP tune they are simply a point of failure.

 

And again, with anti-lag a BOV would defeat the whole purpose. When you run a rally-style anti-lag, even when you close the throttle, it is still introducing air past the throttle plates. Of course it would be stupid to run a BOV if the throttle is never actually shut and you're still trying to cram pressurized air in the engine between shifts.

Now, who said rally teams or other were concerned enough about turbo longevity to even test whether a BOV would actually help in that aspect?

 

how many miles of rally racing equals the same mileage of a street driven car?

they are the epitome of abusing their ****, and they dont often break down the cars in between stages.

 

+1

It is very sad when some people ridicule these examples, because they come from racing scene...
As has been said, rally cars, endurance cars from Group C era, F1 cars etc. all run without any BOV. And in case of endurance cars, running 24 hours, almost 5000 km of full load, there is nothing to discuss. If it would prolong life or enhance reliability, sure, they would use it,but they didnīt. It must be some secret sauce

Most people who are arguing in this thread are confusing things what they read - heard about compressor surge - this is not happening here

 

I think one of the things that confuses people is that their "mates" turbo failed when they removed the BOV 180,000km into turbo car's life, after doubling the factory boost pressure.

Lets have a think about that. Bearing wear is proportional to square of speed. Out of balance forces are proportional to the square of speed. Thrust force from turbine wheel due non linear exhaust pressure rise is proportional to a partial power of intake pressure (due to less than 100% efficiency of turbine & compressor), shaft speed is roughly proportional to boost pressure (in the meat of the map anyway) .

so bearing wear on an already flogged out turbo then gets >> a doubling of speed*increased load thrust(2*1.5 rise factor).
(2^2)*2*1.5 + out of balance=12+ times the thrust bearing wear rate his shitty old turbo was seeing, already degraded, under load, where you spend much much much more time than on gear change tranisents. Definately the BOV that killed it

This is not to mention that many guys see much more significant transient loads from the turbine wheel due to audible or inaudible missfires, ignition cut rev limiters or two steps (explosion in your exhaust manifold anyone) in a much more confined space than intake/plenum/pipework which almost always blows off if they get an intake backfire despite the force being far less concentrated by a more restricted volume.

Fact is to get a responsive turbo/engine package that has more under the curve in a street car you need to work a (slightly smaller than many use) turbo harder for the best performance compromise, but compared to industrial diesels (or real race cars that spend more than 10 seconds on load by a factor of lierally thousands ) that do literally thousands of hours, not just idling the turbo over like spark ignition engines do at cruise, but actually working on load at boost, pushing & pulling loads all day, we must be getting a lot of shittily manufactured and assembled turbos in the after-market. Even a daily driver/track car that gets thrashed "mercilessly, all the time" only sees a tiny fraction of the duty a circuit racer or working machine sees.

 

It was an HKS Sports hotside/CHRA (O-trim exhaust wheel) with a 35R compressor wheel/back plate.

I think I'll gracefully bow out of this conversation now. I've always liked the way of the osterich, you can't hear bullshit with your head buried in the sand.