hmm im going to take my bov off of the stock system just to test it. If it blows my old crusty stockers oh well I guess its single time.

haha that made me laugh.

Just took it of and did some initial testing, I was expecting some flutter but no it just sounds like a lower pitched bov. On a side note stock non seqs dont hit 10 psi til almost 5k in 2nd gear, never really noticed that before lol and ive been DDing it like this for years

My HKS BOV leaks... hmm

Bov's are not needed ran without one for 20k on my s2000 when i was turbo'd people think it will surge the turbo but it wont. you have nothin to worry about. :-D keep everyone posted just so you can prove most wrong. :-D



Edit i was at 650 whp to at 26 psi. and beat the hell out of it at that.

Ok it's been a year and almost 3000 miles of boosting. Turbo hasn't blown yet, no noticeable problems.

https://www.rx7club.com/members/thatpoorguy-131086/

I tried to see if he made a thread about it. BUt this forum member claims his stock twins shaft snapped due to his vacuum line comming of his BOV.
I searched a little but not much info on it.
HE has the carnage in his photo album

I personally used to own an 86 300zx turbo. besides the fact that z31 engines run 5-6 psi. The factory POV(pop off valves) do get plugged for performance and ran up to 13.5 psi like that.

Its up in the air. MY z ran without one for 2 years. And my 7 has used one for 5 years.

Ive been running 13psi on the stock twins with it deleted for a little over 1k miles now. My turbos already smoked a little bit on startup for a few seconds and Ive seen slight traces of oil in the IC lines in the past before deleting it. Nothing has changed since deleting the bov, still same amount of smoke and no increase in oil in IC lines.

I was hoping it would be devastating to the turbos or somehow blow the engine so I could get motivated to install a fresh rebuild in my car but no dice. I will be running my 500R without a BOV whenever I find time to install it.

Lots of reading in here.

I have a couple of questions. Dj did you notice any performance improvements on the twins? If you actually boost higher between shifts do you need to retune the car to accommodate the extra cpl psi? Could that explain why the one car above was jerking, even though it ran quicker times?

Finally if you delete the bov that is almost the same concept as running the re circulating bov right?

First of all, remember that 3rd gen car and a 2nd gen with a standalone EMS don't have an airflow measuring device in the intake, so there are no potential driveability issues related to that.

Now on a recirculating BOV (an air bypass valve) the pressure waves are relieved through the valve to the low pressure (inlet) side of the turbo, before the blades. Without an air bypass valve the air goes back through the turbo itself and out the inlet.

The debate is whether, upon lifting the throttle, relieving the pressure through the turbo itself (no air bypass valve at all) will damage the turbo or hurt response. One argument is that it will quickly cause damage to the turbo. That has been mostly refuted. I haven't had a BOV operating for a couple years now, but with my projects and the way I drive my car that's about 5000 hard miles boosting anywhere from 16 to 21psi.

Some say running no air bypass valve will shorten turbo life over time. There are a couple turbo cars that have been mentioned which came without one from the factory. As for longevity debates in these Rx-7 applications, well there are people like me testing this just for the heck of it really.


The whole debate about turbo spool and response which surrounds air bypass/blowoff valves is tricky. There is a lot of marketing hype around aftermarket BOV's because people are trying to sell products. There is also more anecdotal evidence indicating the opposite--that BOV's don't really make much of a differerence, or that they actually hurt response. And that's the kind of thing that is frustrating to sort through. What compounds the confusion is hearing claims from people with airflow meters (Evo, STi), because keeping that sensor happy can also improve the way the car drives. I think one of the only way to settle this will be to get datalogs from a turbo tachometer but Google tells me they are like $1600.

$425

http://www.atpturbo.com/mm5/merchant...egory_Code=BCS

How hard fitting is, esp to non Garrett turbos, I have no idea.

Cant believe this thread went 5 pages(i only read 2),why dont people listen to people that have been there done it! rx72c has proven that you dont need one,I have ran many turbo track cars with out bov's without any issues and they responed better between gears without ya gay bov.all with plain bearing turbos aswell.
rx72c I feel ya pain buddy,trying to explain to people how shit happens and they just dont listen because they THINK it cant work:lol:

I notice less pressure drop between shifts but it is minimal. I am using a mazdaspeed short shifter and shifting using the clutch like a normal person drives on the street. You arent going to see vast response difference, it was just another thing to delete from the engine bay. Getting used to the sound is a little difficult, I prefer my car to be quiet and it is far from it with the BOV deleted. Ive since put another 1k miles or so on the car since the last post with no ill effects.

I am now at like 3k miles without a BOV.

My reasoning is that if I have an antisurge housing that can prevent true harsh on throttle surge I doubt a flutter with no throttle is goin to hurt it.

Damn. That's not a bad price considering the other options. I bet it's some kind of square wave signal that can't be easily/cheaply datalogged though.

[IMG][/IMG]

And that's why the Mazda describes the factory air bypass valve as a noise reduction device...

^I'm not running one right now. I re-did my IC setup and just didn't get a flange on my new piping for one. I don't drive too much, and when I do, I don't boost too hard (needs tune, waste gate). However, it really does sound ODD. The fluttering on my car is very loud. Personally, I prefer NO noise. I want to put one back on and route it to the filter/turbo inlet.

lazy man post
 

So I haven't read every post because I am lazy, but anyone who works in the industry fears the terms "unexpected/unintended motion" in a DFMEA review. Toyota had some fun with that one. Not running a BOV can cause this.

The all of the stock cars (that I know off) that do not run a BOV/POV have a fuel or ignition cut programmed in, which is not ideal in IMO. On a race car it's no issue, but anyone who has had a car surge on them knows it can be difficult to handle. My car use to surge at the top of 1st & 2nd gear causing me to bounce off the rev limiter. (I had sticky secondary throttle plates, stiff BOV, and I run a map sensor) If you get blocked from passing you can end up swapping paint. Either way you don't get out of the corner right.

I understand that with all new equipment and a good tune you may not need one but who wants to worry? A BOV is cheap. I run a CXracing BOV, supercheap and works great.

The best theory I've heard is that you can only have two of the following fast/cheap/safe in a race car. Most of us go cheap and fast. :lol:

That's my two cents...

Cheap BOV endup costing you more. I had a Jeg's one that came on a TII I picked up. It stuck open/closed too slow and caused some issues. With my current setup running the Greddy Type S it isn't an issue. If I were to build my setup again I wouldn't use a BOV. But it would cost me more to redo the piping to get rid of my bov flange, so BOV is staying for now.

What does compressor surge due to mismatched turbo have to do with not running a BOV? Unless I mistook what your trying to get at?

Not running a BOV, isn't about cheaping out. It's that fact that it may in fact not be needed, one less thing to fail, cleaner engine bay, and that it possibly increases turbo response after a shift since the IC/pipes don't depressurize. A lot of members that have tried it have claimed it does have a noticeable affect on boost response after a shift.

I run an undersized BOV on my car and it flutters every time i shift which gives the car a unique sound. I've been considering removing it but haven't decided yet hehe. It's one of those things I'll probably get to when everything else on the car is the way I want it running.

thewird

I don't think anyone in here is advocating that you run a turbo that is mismatched to your engine. This can cause damaging compressor surge under heavy load driving and there is no debate about that. That type of compressor surge is separate from the question of what should happen to the charge air after you close the throttle.

Btw, I was dynotuning a streetported GT40 FD on Friday and the Turbosmart BOV was causing a massive boost leak. We were wondering why we couldn't break 300 to the wheels at 14psi on a Garrett GT4094R turbo. It took us a while to figure it out because the atmospheric wastegate dump was so loud that you couldn't hear anything else. Of course a good BOV that has been installed and adjusted properly will not cause a boost leak.

Let me clarify,

Depending on your system and the condition of your parts you can have a "surge" with a matched turbo. For me it occurred at high RPM shifts (7500 + rpm) near redline in low gears in combination with a sticky throttle and a stiff BOV. It took all three of these conditions to cause the issue. It theory it can happen any time you have a turbo.

I sorry but "clean engine bay and one less thing to fail" sound like excuses. Not knocking your opinion, I just don't agree.

I understand running no BOV can decrease spool time after shift but if you have the right turbo you should not have delays between 2-3, 3-4, and 4-5. In 1-2 shifts it can be beneficial IMO to have a slight drop in boost/power so you don't light the tires up. It's kind of like the auto-traction method (shift above peak torque).

Maybe people have issues with BOV because they shift slow, and don’t put enough right foot into it.

:101384_l:

^
I am missing your point, your turbo surging has nothing to do with the BOV so why are you claiming it caused the problem?

CBR. dont waste your time. i am learning slowly. People do not want the word from people with real world experience who are willing to share info you have to pay good money for. They would rather go on their own theories.

You have an issue somewhere. With HKS downpipe(restrictive), resonated midpipe, and Greddy SP I hit 10 lbs around 38-3900rpms in second.

Any body data log pressures before and after throttle plates yet? If the pressure spike is the same with and without BOV I would buy into this, but I would have to see more than "I haven't had issues yet". That's not a good way to find out IMO.

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

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

last post
 

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.

https://www.rx7club.com/attachment.p...1&d=1282093032


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.

^ http://www.brukbar.no/brukcms/data/u...t-see-shit.jpg

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 shit, 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 didn´t. It must be some secret sauce:lol:

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

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 :lol:

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 :lol:) 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. :nod: 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. :lol: