Anyone here run without a BOV?

[yoshimitsuspeed]

I don't hang out on the DSM forums much these days.
I do still come here from time to time due to the fact that there are a lot of people who know a lot about running boost and making power.
My Baby for the last 10 years has been a MK1 MR2 which is now running a blacktop 4AGE at 11:1 compression and 7 PSI boost on a DSM T25.

Anyway occasional I stumble into the MK2 MR2 forums because there is a lot more turbo talk and knowledge there than in the MK1 section.

There is a pretty big movement at this point of people not running a BOV. In fact it seems more like the black sheep who do these days.
You have to be a member to view the MR2OC so I won't drop a link but I'll throw a couple quotes from pro no BOV supporters.
I did a search and couldn't find anyone here talking about it.
Give me your thoughts. I'm looking for people who really know their stuff.
If you are going to tell me everyone should run a BOV because that's what you were taught or because that's the standard don't bother.
I'm looking for knowledgeable educated thoughts on this.

The sound is the compressor screaming "help meee....!"

It is not!

Running no BOV does not damage the turbo, or effect its lifespan.
BOV's were introduced as a NHV prevention measure, that is all.
Running without a BOV does decrease lag on gear changes.

When will people learn...

This is never going to be proven.

I think its fine to not run a valve. The logic makes sense to me.

However, you have the guys who run valves who are fine. You have the guys who dont run valves who are fine. And you have the guys who do both and lose turbos both ways.

My only response to the bov is needed crew is this: Toyota ST185 AllTracs/GT4s didnt come stock with one, and their turbos get about the same life out of them as ours do.

I took mine off in 2009. I got a lot of sh○t for it when I first started talking about the idea in 2008. I've had my turbo apart several times since then for upgrades, etc, and never seen any damage that could be attributed to it. I've run boost as high as 3.0 pressure ratio on it (~29psi at sea level), though I've had the boost turned down lately due to head lift. I'll be turning it back up once I retorque the head.

I think that covers the high points.
I could dig up pages upon pages of similar content.
Tell me what you think.

 

[cavyracer666]

isn't one of the main reasons for a bov so that when the throttle shuts an excessive amount of pressure isn't applied to the throttle plate. I've heard of people bending throttle plates like this. however if it was a race vehicle with no lift to shift I guess that wouldn't be a problem as far as the throttle plate is concerned

 

[WES_393]

I don't think it's totally a matter of lifespan, but more about performance. In my experience, off-throttle compressor surge (or "turbo flutter") can mess with perfromance in 2 different ways.

1. By messing with the MAF signal. When the air has nowhere to go, it flows back past the compressor wheel causing that well-known fluttering noise. Those pressure waves are picked up by the MAF sensor and show up on the log as oscillating spikes of airflow. I have seen this first-hand when I had a flutter-happy Crushed 1g BOV. And that skewed airflow reading naturally had negative effects on the ECU's fuel control, sometimes to the point of stalling the engine. Now, the ST185 does not have a BOV from the factory, that is true. A good friend of mine has one and I have personally worked on it multiple times including a top end rebuild. However, it does have a "harmonic intake" which is basically a little door between the turbo and MAF. It's my thought that this not only stops the flutter noise for NHV purposes, but also reduces the effects of those pressure waves.

2. Slowing down the compressor. It's simple physics, if the compressor rotates one way to move air in one direction, then air moving in the other direction will try to force the compressor rotation in the other direction. It's a pretty well busted myth that the compressor will stop or reverse direction, but it will slow down as a result. If that's not true, why would companies like Holset spend the valuable time and resources equipping their stock turbochargers (which are used on engines without a BOV) with anti-surge housings? It must have an effect of shaft speed, and possibly service life as well.

 

[yoshimitsuspeed]

isn't one of the main reasons for a bov so that when the throttle shuts an excessive amount of pressure isn't applied to the throttle plate. I've heard of people bending throttle plates like this. however if it was a race vehicle with no lift to shift I guess that wouldn't be a problem as far as the throttle plate is concerned

This is very important with a fixed displacement supercharger since the pressures can get much higher. I have never heard of anyone bending or breaking a throttle plate with a turbo setup. If you know of any easy to find links I would love to see them.

I don't think it's totally a matter of lifespan, but more about performance. In my experience, off-throttle compressor surge (or "turbo flutter") can mess with perfromance in 2 different ways.

1. By messing with the MAF signal. When the air has nowhere to go, it flows back past the compressor wheel causing that well-known fluttering noise. Those pressure waves are picked up by the MAF sensor and show up on the log as oscillating spikes of airflow. I have seen this first-hand when I had a flutter-happy Crushed 1g BOV. And that skewed airflow reading naturally had negative effects on the ECU's fuel control, sometimes to the point of stalling the engine. Now, the ST185 does not have a BOV from the factory, that is true. A good friend of mine has one and I have personally worked on it multiple times including a top end rebuild. However, it does have a "harmonic intake" which is basically a little door between the turbo and MAF. It's my thought that this not only stops the flutter noise for NHV purposes, but also reduces the effects of those pressure waves.

2. Slowing down the compressor. It's simple physics, if the compressor rotates one way to move air in one direction, then air moving in the other direction will try to force the compressor rotation in the other direction. It's a pretty well busted myth that the compressor will stop or reverse direction, but it will slow down as a result. If that's not true, why would companies like Holset spend the valuable time and resources equipping their stock turbochargers (which are used on engines without a BOV) with anti-surge housings? It must have an effect of shaft speed, and possibly service life as well.

I have presented these theories and plenty of others have as well.
As for the AFM/MAF. This fluttering is only going to happen off throttle. At that point you aren't looking for performance. If you are completely off throttle (at least with my MR2 and many other cars) fuel is cut completely so the only time it would be the slightest issue would be at those times where you let most of the way off the throttle but not all the way.

As for slowing down the compressor, this one was the hardest for me to swallow.
Many people swear they get quicker spool on shifts and quick throttle of then on transitions without a BOV than with. I rarely trust people opinions judging something like this however I have now seen several logs showing boost response with the BOV and without and the turbo does indeed appear to make boost faster without.
One big point and where it is the most important is on quick shifts or quick lifts. Since the pressure charge is still in the intake when you step on the gas you are already feeding a larger mass of air into the motor and therefore more exhaust gasses coming out of it more quickly speeding up spool.
I have seen datalogs that seem to confirm that this outweighs any loss from slowing the compressor.

 

[WES_393]

I have presented these theories and plenty of others have as well.
As for the AFM/MAF. This fluttering is only going to happen off throttle. At that point you aren't looking for performance. If you are completely off throttle (at least with my MR2 and many other cars) fuel is cut completely so the only time it would be the slightest issue would be at those times where you let most of the way off the throttle but not all the way.

Sure, if your in gear and let off the throttle. But if you do a quick pull and then shift to neutral to coast, the ECU resumes closed loop operation. Thats why DSMers have such an issue with stalling when venting to atmosphere- It messes with closed loop.

As for slowing down the compressor, this one was the hardest for me to swallow.
Many people swear they get quicker spool on shifts and quick throttle of then on transitions without a BOV than with. I rarely trust people opinions judging something like this however I have now seen several logs showing boost response with the BOV and without and the turbo does indeed appear to make boost faster without.
One big point and where it is the most important is on quick shifts or quick lifts. Since the pressure charge is still in the intake when you step on the gas you are already feeding a larger mass of air into the motor and therefore more exhaust gasses coming out of it more quickly speeding up spool.
I have seen datalogs that seem to confirm that this outweighs any loss from slowing the compressor.

I might just try this myself and see what I get...

 

[yoshimitsuspeed]

Sure, if your in gear and let off the throttle. But if you do a quick pull and then shift to neutral to coast, the ECU resumes closed loop operation. Thats why DSMers have such an issue with stalling when venting to atmosphere- It messes with closed loop.

It is a little bit different though.
If you vent your BOV the ECU is dumping fuel for air that has already passed past the AFM/MAF but is not going into the engine.

Without a BOV if you let off the gas the volume of air is going the exact same place it would with a recirc BOV it's just taking a different path. It should have a similar effect. If the air was still fluttering while you stepped on the gas it could confuse the ECU a bit but that overlap should only be a few ms if anything.

If you do try it I'd love to see your results.

 

[ZenkaiRacerDsM]

I don't see the point unless you just don't want to pay for a BOV. I'd rather have the best of both worlds with a BOV.

My BOV doesn't open while running down the track and no lift shifting.

 

[JusMX141]

DON'T think about doing it unless you have a ball bearing turbo. Above a certain boost level, a journal bearing can't handle the surge from the shaft load....even if it's surge-ported.

Good friend of mine forgot to hook up his BOV signal line from the manifold after installing a new trans mount one night. Drove the car around like that for two weeks before he noticed it and hooked the line back up- two days later, death whine from the turbo. That was at about 25psi with a 20G.

 

[DSMsOwnYourV8]

DON'T think about doing it unless you have a ball bearing turbo. Above a certain boost level, a journal bearing can't handle the surge from the shaft load....even if it's surge-ported.

Good friend of mine forgot to hook up his BOV signal line from the manifold after installing a new trans mount one night. Drove the car around like that for two weeks before he noticed it and hooked the line back up- two days later, death whine from the turbo. That was at about 25psi with a 20G.

Yeah... I don't understand why people constantly try to reinvent the wheel. BOVS are engineered for a reason. Use them.

 

[rrussell]

Don't do it!!!

I killed a perfectly good evo III 16g turbo in about a month running with a bad BOV. I thought well I'm running a auto so it shouldn't be that bad?

After a good pull getting onto the freeway and letting off at 30psi. I noticed the turbo started making a whining sound and then at the next stop at light load she gave up and completely stop turning. Limp it home and took the turbo apart to find the compressor wheel was lightly hitting the compressor cover. Also on the turbine side the seals were pinch to the point I can't even get part of one out.

So now I have a low mile 16g as a paper weight in my office to remind me, always run a BOV.

 

[Steve93Talon]

DON'T think about doing it unless you have a ball bearing turbo. Above a certain boost level, a journal bearing can't handle the surge from the shaft load....even if it's surge-ported.

Good friend of mine forgot to hook up his BOV signal line from the manifold after installing a new trans mount one night. Drove the car around like that for two weeks before he noticed it and hooked the line back up- two days later, death whine from the turbo. That was at about 25psi with a 20G.

While I agree with what you're saying, in all fairness your friend's example is far different from running with no BOV. He had no boost pressure to force the valve shut, creating a massive boost leak leading to over-spinning the turbine shaft.

 

[pearl4gtsi]

Many people swear they get quicker spool on shifts and quick throttle of then on transitions without a BOV than with. I rarely trust people opinions judging something like this however I have now seen several logs showing boost response with the BOV and without and the turbo does indeed appear to make boost faster without.
One big point and where it is the most important is on quick shifts or quick lifts. Since the pressure charge is still in the intake when you step on the gas you are already feeding a larger mass of air into the motor and therefore more exhaust gasses coming out of it more quickly speeding up spool.
I have seen datalogs that seem to confirm that this outweighs any loss from slowing the compressor.

I understand the logic behind this, but don't you get just the same when you recirc the bov?

I know you said you've seen logs where it indeed appears that with no bov you get quicker spool.... But to save many people the headache of POSSIBLY destroying there turbo, why not keep the bov, recirc it, and have the best of both worlds.. turbo safety and quick spool when shifting?

Just my 2 cents

 

[yoshimitsuspeed]

I don't see the point unless you just don't want to pay for a BOV. I'd rather have the best of both worlds with a BOV.

My BOV doesn't open while running down the track and no lift shifting.

That might be easy enough on the drag track but it's not always the ideal option.

I'm not afraid to say I played the role of the pessimist for a long time on the MR2 boards. I'm still not fully convinced either way but since most here seem to be pessimists I'll try to play devils advocate to the best of my ability.

DON'T think about doing it unless you have a ball bearing turbo. Above a certain boost level, a journal bearing can't handle the surge from the shaft load....even if it's surge-ported.

Good friend of mine forgot to hook up his BOV signal line from the manifold after installing a new trans mount one night. Drove the car around like that for two weeks before he noticed it and hooked the line back up- two days later, death whine from the turbo. That was at about 25psi with a 20G.

This guy runs 16Gs and 20Gs.

I took mine off in 2009. I got a lot of sh○t for it when I first started talking about the idea in 2008. I've had my turbo apart several times since then for upgrades, etc, and never seen any damage that could be attributed to it. I've run boost as high as 3.0 pressure ratio on it (~29psi at sea level), though I've had the boost turned down lately due to head lift. I'll be turning it back up once I retorque the head.

Yeah... I don't understand why people constantly try to reinvent the wheel.

This is silly logic. People are constantly trying to reinvent the wheel and constantly figuring out ways to squeeze more hp, better gas mileage, less emissions etc out of setups that people just wouldn't believe 5 years earlier.

BOVS are engineered for a reason. Use them.

What is that reason? Is this knowledge that you have gained through engineering turbo systems? Ir is it knowledge you have gained that has been passed down through the generations of tuners and internet forums?

Don't do it!!!

I killed a perfectly good evo III 16g turbo in about a month running with a bad BOV. I thought well I'm running a auto so it shouldn't be that bad?

After a good pull getting onto the freeway and letting off at 30psi. I noticed the turbo started making a whining sound and then at the next stop at light load she gave up and completely stop turning. Limp it home and took the turbo apart to find the compressor wheel was lightly hitting the compressor cover. Also on the turbine side the seals were pinch to the point I can't even get part of one out.

So now I have a low mile 16g as a paper weight in my office to remind me, always run a BOV.

This is interesting. I don't hang out all that often on the MK2 MR2 boards but I have yet to hear of one failure that could be attributed to running without a BOV. There are quite a few people over there running considerable boost with no BOV.
Are you sure it wasn't leaking like Steve93Talon mentioned? Or possibly some other related or not related reason?

I understand the logic behind this, but don't you get just the same when you recirc the bov?

No, the benefit is having the pressure charge in the intake piping post turbo. It takes longer to bleed this pressure off through the compressor whereas the BOV bleeds it off almost instantly.

With no BOV you let off the gas and then as long as you give it gas while there is still pressure in the system that higher pressure charge rushes into the engine and gives it a boost of power and increased exhaust flow that spools the turbo quicker.

 

[johnovision27]

Straight up, Compressor surge is not considered "normal operation" for any turbo, engine, etc. It's abnormal and usually a bad situation. Ask any airline pilot out there (mind you, their situation is far worse as they're in the air, but the same principals apply)
Run a BOV, stop being a cheap arse, and stop trying to go against the grain when you have zero evidence to support your wild and crazy theories.

 

[rrussell]

This is interesting. I don't hang out all that often on the MK2 MR2 boards but I have yet to hear of one failure that could be attributed to running without a BOV. There are quite a few people over there running considerable boost with no BOV.
Are you sure it wasn't leaking like Steve93Talon mentioned? Or possibly some other related or not related reason?

I actually did a boost leak test before I took the turbo off the manifold. I thought at first a major charge pipe or boost leak was the problem. Then when I started the engine back up after the test i noticed the compressor wheel wasn't turning.

 

[yoshimitsuspeed]

Straight up, Compressor surge is not considered "normal operation" for any turbo, engine, etc. It's abnormal and usually a bad situation. Ask any airline pilot out there (mind you, their situation is far worse as they're in the air, but the same principals apply)
Run a BOV, stop being a cheap arse, and stop trying to go against the grain when you have zero evidence to support your wild and crazy theories.

Like I said, If I took the time I could find pages upon pages of dozens of people running no BOV and many of them at very high boost. I have also not yet heard of a failure that could be directly linked.
I have also made it clear that these are not my theories but I am looking for input from people who can explain their reasoning behind agreeing or disagreeing.
Regardless I don't need people telling me what to do or how to think.
I am looking for an intelligent educated conversation on a controversial subject.

On throttle compressor surge is a very bad thing and I would find it especially disconcerting in an airplane. Due to the nature of an airplanes throttle operation and manner of use I doubt there is much occasion where there would be off throttle surge.
In fact I wonder if any airplane even runs a BOV?

 

[jakelandry]

FWIW, I toasted a hx40 (factory surge-ported and designed for a non bov vehicle) from doing the dgm bov mod and not running the bottom port. 80 mph on the highway created enough surge to cause journal wear signifigant enough to eat my compressor cover and billet wheel up. Ask justin, he rebuilt it... twice. Not saying no bov kills turbos, just adding my experience.

 

[yoshimitsuspeed]

80 mph on the highway created enough surge to cause journal wear signifigant enough to eat my compressor cover and billet wheel up.

From your description this sounds like on throttle surge which is very bad and unrelated to the BOV. Is that the case?

An anti surge housing really just moves the surge line to the left on the map so it's still quite possible to get surge with an anti surge housing it's just less likely.

 

[DSMsOwnYourV8]

This is silly logic. People are constantly trying to reinvent the wheel and constantly figuring out ways to squeeze more hp, better gas mileage, less emissions etc out of setups that people just wouldn't believe 5 years earlier.

Silly logic is trying to outsmart/question engineers who design one turbocharged car after another. Squeezing extra ponies out is one thing, doing a mod that puts your turbo at risk and has no real added gain is another.

 

[rrussell]

Also in my case the thrust plate had around a .050 groove cut in it. In fact all the parts that take side to side thrust were f'd up. It had great oiling. The shaft and bearing showed no signs of lack of oil.

This was a OEM evoIII 16g with less then 4k on it that I only ran about three 28psi
full passes on. Before that it was only at 18psi.

 

[jakelandry]

From your description this sounds like on throttle surge which is very bad and unrelated to the BOV. Is that the case?

An anti surge housing really just moves the surge line to the left on the map so it's still quite possible to get surge with an anti surge housing it's just less likely.

My daily commute is fairly hilly, and according to my avcr after topping a hill the throttle cuts from around 25% to 1-3%, enough to cause what I would consider "off throttle" compressor surge. While its not a 30+ psi or 50lb/min flow, it was significant enough to ruin an evo 3 and hx40. Evo 3 got about 7k miles and the holset went within 4k miles, both extreme journal wear. And yes it is still possible to surge, especially on a 2l motor. That compressor cover is designed to reduce surge on motors that consume what 5 lb/min just to remain running?

 

[yoshimitsuspeed]

Silly logic is trying to outsmart/question engineers who design one turbocharged car after another.

Well then the same could be said for running a boost controller, crushing the stock BOV, or really changing any other part of your car.
More importantly unless you are one of those engineers, have talked to one of those engineers or were educated based off the science that they used you don't know their reasons for doing it. I don't question them, their engineering ability or their reasons for doing it. Obviously it was worth the time and money to add to most cars. What if it was purely NVH? Can you prove it wasn't?

Once again

Toyota ST185 AllTracs/GT4s didnt come stock with one, and their turbos get about the same life out of them as ours do.

Now why didn't they feel that one of the greatest rally cars of it's time and a car more commonly used for racing and high performance driving than many cars did not need a BOV?
Some say because it was a low production car aimed at the kind of people who wouldn't be bothered if their car sounded like a wounded pigeon every time the let off the gas.
What's important is that they last very well.
Now it's possible they had modifications made to the turbos but if so it's not something noticeable.
So at some point some group of engineers and designers decided a BOV wasn't needed in at least some applications.
There are a number of other cars that don't have OEM BOVs though most of them do run lower boost.

I actually did a boost leak test before I took the turbo off the manifold. I thought at first a major charge pipe or boost leak was the problem. Then when I started the engine back up after the test i noticed the compressor wheel wasn't turning.

Was your boost leak test done up to the pressure of boost you were running? Did it include the BOV circuit to make sure the BOV wasn't bypassing under full boost?

 

[JusMX141]

I'm a bit confused- are you here looking for input as the last line of your first post suggests, or are you only here to tell us all that we're idiots for using a blow off valve?

 

[Alex7747]

I'm a bit confused- are you here looking for input as the last line of your first post suggests, or are you only here to tell us all that we're idiots for using a blow off valve?

Thats the same feeling i got after reading a couple of his posts...

And for the record, about a year ago i bought a cheap ebay BOV and it was leaking and needed my car then and didn't have the money to buy a legit BOV so i decided to use the car without a BOV. The cars performance did improve (I'm sure its because it was leaking before and no other reason) but it was surging all the time. About a week later i got a new BOV and everything was back to normal. Turbo never had shaft play or anything bad ect. It was a s16g on about 17psi, so that it for what its worth .

 

[yoshimitsuspeed]

I'm a bit confused- are you here looking for input as the last line of your first post suggests, or are you only here to tell us all that we're idiots for using a blow off valve?

Lol, I already told you. I'm here to play devils advocate and since everyone here seems pretty pro BOV that means me backing the other side of the argument. If everyone here were proud members of the no BOV club I would be playing the other side. If I wasn't supporting the other side we wouldn't exactly have much of a conversation going on would we?
I haven't made any personal accusations or even included much of a personal opinion one way or the other so why do you feel so attacked by someone coming in and questioning a longstanding belief?