Curious: Recirculating BOV Towards Turbine Wheel

[98GSXin]

I got to thinking again about new ways to make things better. This idea is completely open to suggestion, criticism and laughter. Just thinking out loud basically... please keep the conversation intelligent respectful.

A typical bov recirculation shoots compressed air back into the intake system at the compressor wheel. It makes sense in practice because it is recycling the boost so that there is as little waste as possible.

But the basic principle of a turbo is that the turbine wheel drives the compressor wheel by use of gas in the exhaust system. So then, wouldn't it make sense to divert the bov recirculation directly into your exhaust towards the turbo so that the extra pressure is used to keep the turbine wheel spinning? After all, the cause of turbo lag is the exhaust gas slowing down between shifts. Replacing your exhaust gas with the extra boost in short bursts could possibly help keep the turbo wheel's rpms up.

Then there are logistics issues in making a connection between your intercooler piping and the exhaust like heat transfer and back pressure from the exhaust on the bov, but that can be sorted out through research and development.

What do you guys think?

 

[Bud92gsx]

Buy an auto....

No but seriously you would have to make a hole in the manifold, and have to have a metal recuirc tube..

I guess It could work in theory, but then who knows It could also be a crapshoot..

On a stock engine, the air is supposed to go back into the intake tube..So you would also have to account for that as well..

 

[98GSXin]

That's why this thread was started! I'm not falling all over myself to go fab this up, but it has piqued my interest. I think that it would be possible with the right skills, time and money to do it properly though.

And I will never buy an automatic vehicle again in my life. Another story for another time... haha.

 

[icekilla126]

I don't think the bov will be able tO handle the back pressure from the exhaust

 

[Bud92gsx]

Auto dsm's are hella fun..They don't loose boost pressure when shifting..

But I like this theory..

 

[kicker91laser]

I don't think it would work. Turbine drive pressure is almost always higher than boost pressure, this would also be the case while out of boost. My thoughts are that the exhaust pressure would back up into the charge-air plumbing if the bov would even open at all. The bov would also have a hard time surviving at the temps coming from the exhaust so you would probably have to run a wastegate as a bov if it did work.

 

[98GSXin]

The bov would also have a hard time surviving at the temps coming from the exhaust so you would probably have to run a wastegate as a bov if it did work.

Forward thinking. I like it. If I were to end up with a good name brand wastegate like Tial, would it stand a better chance resisting the exhaust back pressure? Or are bovs just not designed to see pressure like that?

What if one were to incorporate a very stiff spring to the inside of the intercooler piping at the bov keeping it in the closed position while being pushed on by exhaust gas?

 

[El Cuervo]

One of the problems here that I see is that eventhough you could get it to work, the extra discharge of fresh air to the turbine would cause a lean condition readout by your o2 sensor and or wide band.

 

[98GSXin]

One of the problems here that I see is that eventhough you could get it to work, the extra discharge of fresh air to the turbine would cause a lean condition readout by your o2 sensor and or wide band.

Which could be compensated for in dsmlink? Not sure, but it seems that you could adjust your fuel trims not to overcompensate because you are already expecting the extra fresh air in the exhaust... It would only be for a split second while you shift anyways and then your normal exhaust would return and give accurate readings.

Or you could place your o2 sensor for the wideband before the turbo?

 

[-red97rum-]

I don't think it would work. Turbine drive pressure is almost always higher than boost pressure, this would also be the case while out of boost. My thoughts are that the exhaust pressure would back up into the charge-air plumbing if the bov would even open at all. The bov would also have a hard time surviving at the temps coming from the exhaust so you would probably have to run a wastegate as a bov if it did work.

That's right. Not to mention the pressure from the exhaust would probably keep the bov from opening all together. Even if you were to try something like this... The amount of air released from the charge pipe when the bov opens is shit compared to what four 85mm pistons are pumping.

*Edit: OP, are you serious or is this a Friday joke?

 

[98GSXin]

That's right. Not to mention the pressure from the exhaust would probably keep the bov from opening all together. Even if you were to try something like this... The amount of air released from the charge pipe when the bov opens is shit compared to what four 85mm pistons are pumping.

*Edit: Are you serious or is this a Friday joke?

The exhaust pressure between shifts would be fleeting so the bov/wastegate would be allowed to open.

This idea wasn't meant to keep making boost, just enough to help keep the turbo rpms up.

And I'd like to call it serious. Even if I don't have immediate plans to attempt it. I want to provoke conversation, debate and innovation.

 

[-red97rum-]

The exhaust pressure between shifts would be fleeting so the bov/wastegate would be allowed to open.

This idea wasn't meant to keep making boost, just enough to help keep the turbo rpms up.

And I'd like to call it serious. Even if I don't have immediate plans to attempt it. I want to provoke conversation, debate and innovation.

Yeah but even if the exhaust pressure is fleeting, how much boost are you running? Even if you're running 30+ psi of boost, compare that to a single cylinder's static compression x 4. Then add air, fuel + combustion and I'm betting it would be a lot more than what is expelled from the BOV. Now I know not all the exhaust pressure is going to blow towards the bov, but I believe the turbine wheel is big enough obstacle to keep the exhaust pressure higher than the air released from the BOV.

I like the way you're trying to find methods of being more efficient but lets not reinvent the wheel here. I'm sure this would have been considered long ago if it was at all feasible. Look at some of the fastest DSM's out there and hardly any of them even recirc their bov's.

 

[98GSXin]

Yeah but even if the exhaust pressure is fleeting, how much boost are you running? Even if you're running 30+ psi of boost, compare that to a single cylinder's static compression x 4. Then add air, fuel + combustion and I'm betting it would be a lot more than what is expelled from the BOV. Now I know not all the exhaust pressure is going to blow towards the bov, but I believe the turbine wheel is big enough obstacle to keep the exhaust pressure higher than the air released from the BOV.

I like the way you're trying to find methods of being more efficient but lets not reinvent the wheel here. I'm sure this would have been considered long ago if it was at all feasible. Look at some of the fastest DSM's out there and hardly any of them even recirc their bov's.

I'm currently at 25 psi on a 65lbs/min turbo with plans for more so there is a decent amount of boost being expelled between shifts.

Once the car shifts, the exhaust pressure towards the bov would greatly reduce as it is ushered out from the tail pipe. At the same time the bov recirculation would be rushing in and only helping speed up this process.

Maybe this hasn't been considered before because the techs at Mitsu decided recirculating to the intake it was enough of a performnce improvement without having to use a heavy duty wastegate on each car that came off the assembly line. And maybe we haven't seen it in track cars because they all are either running automatic or have more sophisticated anti-lag systems.

I think it's important to at least double check your wheel for imbalances, even if it is already perfectly round...

 

[kicker91laser]

Man, I just don't think this would work. If you want to keep boost up between shifts, use NLTS.

 

[98GSXin]

My transmission and clutch setup couldn't take NLTS right now... But this is kind of what I was getting at with the more sophisticated anti-lag systems drag racers are using instead of innovating further with the mechanics of the turbo system.

 

[JusMX141]

This is all great, but....what is your system going to do at idle, when the BOV should be open only slightly to allow the system to go into a "loop" mode when the throttle plate is 100% closed? The running engine will still be making exhaust, and the exhaust pressure will far outweigh the intake pressure at idle, so the exhaust will be trying to travel into the intake. No bueno.

There are far more negatives in regards to this idea than positives.

- How do you effectively separate the exhaust gas from the intake air charge?

- The turbine wheel and all of the parts on that side of the turbo will be at 1500*f, and you're wanting to dump 100*f air into the housing. What do you think that quick charge of cool air will do to the metals?

Regardless, under a full race condition with no-lift shifting, even a standard BOV system hardly has time to do what it's designed to do. Watch some in-car videos of guys tearing down the track and see if your concept is really going to make a significant difference in the way their turbo spools.

 

[SrKegler]

Got to agree with Justin. I would like to add that this type of thinking is what owning a DSM is all about.

If no one ever tried new things we'd still be running 14 sec quarters.

 

[PieEyedPiper]

This automatically made me think of trying to improve a river by paddling water in the direction of flow.

 

[98GSXin]

This is all great, but....what is your system going to do at idle, when the BOV should be open only slightly to allow the system to go into a "loop" mode when the throttle plate is 100% closed? The running engine will still be making exhaust, and the exhaust pressure will far outweigh the intake pressure at idle, so the exhaust will be trying to travel into the intake. No bueno.

Speed density? Does a bov still stay open in a loop when people run with that?

The temperature is something I haven't been able to wrap my head around... still thinking I suppose. haha.

This automatically made me think of trying to improve a river by paddling water in the direction of flow.

It would make you go faster in theory. Two forces in the same direction on the same object make a larger force. It's physics or something like that...

 

[standard235]

They do something similar to this in rally cars.

I heard about it on DS-MAP. I just can't remember what it was called.

EDIT: Ahh a quick Google search saves the day. I introduce to you, AntiLagSystem, methods of new and old.

http://en.wikipedia.org/wiki/Antilag_system

 

[ed1380]

Forget about recirculating before the turbine wheel. Go straight for the high horsepower stuff used by the v8 guys. Its called direct exhaust injection

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[jrohner]

My transmission and clutch setup couldn't take NLTS right now... But this is kind of what I was getting at with the more sophisticated anti-lag systems drag racers are using instead of innovating further with the mechanics of the turbo system.

Once you get it set right, there's no reason it's going to be hard on your clutch or trans IMO. When you first start playing with it, it can be easy to fry your clutch if you're not careful though.

 

[JusMX141]

Speed density? Does a bov still stay open in a loop when people run with that?

It wouldn't be a "loop" because the air is being metered post-turbo....it's unnecessary for the air to be recirculated in that situation. The valve should still be open a tiny bit at idle so the small amount of airflow the turbo is generating has a way to escape the closed throttle plate....especially while the turbo is spooling down.

 

[PieEyedPiper]

Speed density? Does a bov still stay open in a loop when people run with that?

The temperature is something I haven't been able to wrap my head around... still thinking I suppose. haha.



It would make you go faster in theory. Two forces in the same direction on the same object make a larger force. It's physics or something like that...

My theory says it won't though. Overcoming the inherent problems within, youd still have the question. What good is it to inject the relatively cool "puff" of relatively thin air, that your typical 1g bov emits, into a blazing hot, pressurized exhaust stream?

IF you could manage the massive pressure issues you'll face at the opposite end, you'll still have to compensate by running SD or a MAF-T, etc. The real problem I'm seeing though is that I'm not even convinced you could blow off at all.

Say you're running 30psi, now say you're seeing something absurd like 60psi of backpressure in the manifold. Guess what, that valve aint opening. Your compressor is gonna eat that charge like a fist to the teeth.

I don't know for sure what backpressure we see at the exhaust manifold, but if it's more than your boost, which it always will be, then how can you expect to be injecting that air into the stream?
Someone may be wanting to argue that some sort of back eddy or scavenging effect may take place and that the flow of the exhaust stream may in fact help pull the bov charge out and into the stream itself.
No. Too much pressure.

I failed before with the river example. While yes, it is physics or something... that 2 forces acting on the same object will yadda yadda yadda, but what I should have said it reminds me of was trying to improve raging rapids by paddling in the direction of flow. My hand would have been swept away with each stroke before I was able to exert any force. To me, that is like having the bov not open. This is pretty much the end of the river analogy, so I don't wanna hear any "but the river swept your hand away and the same will happen to the bov discharge" stuff

EDIT: Ack! I can't read for shit apparently. I somehow missed like 5 posts and just ended up ath the bottom of the page. Sorry for sounding like a broken record.

EDIT II: Wait, so in that wiki link, it states that in 1995 the Evo III also had a dual system that diverted the bypass charge into EACH of the exhaust runners? OK. maybe on the rally cars, I don't know. I've never seen one in person. But then it goes on to imply the SAS in the evo is there from the factory and of the same design.

Does anyone have any info on how the evo's implement this system? I've never seen an OEM manifold with injection ports. Would it require special ECU tweaks to get the backpressure low enough to allow the bov to operate properly or is there enough of a "lull" between shifts that it just works on it's own?

EDIT III: Oh lawd. I'll never forget the beater corvette with the DEI idea.

 

[JusMX141]

Something else to remember is that the exhaust leaving the cylinders will always have more pressure, velocity, and energy than the air entering the engine because it's being further compressed by the engine itself...this is proven by exhaust pressure on non-turbo engines as well. It would make me wonder how much turbo pressure on the cold side would be required to overcome the pressure that exists in the exhaust manifold before it would even begin to make a noticeable decrease in spool time.