Is a BOV needed?

[FlyTalon]

Do i need to run a BOV or recirculating valve in my car or could I just connect the two wit a piece a pipe?

 

[Jebus[tuning]]

Have fun wrecking your turbo.

 

[LandoAWD]

Yes, you need one.

Search around a little.

 

[SpeedFreak03]

Yea, let me explain why (then you will understand and believe us ). Ok normally, the air goes through the turbo, and into the IC and then the throttle body. Smooth flow, no resistance, its all good. But then, you shift! So, you let off the gas, and the throttle plate slams shut. Now, the compressor wheel (in the turbo) is still pushing that air really hard, but the air is hitting the throttle plate! This extreme force (15PSi or more of air being pushed into a "wall") sends a shock through the whole intake system, back to the compressor wheel. This is called compressor surge. Now if this happens a couple times its okay, but it will start to take its toll on the compressor wheel.

So the BOV comes into play. When you let off the gas, the throttle plate slams shut, but instead of that air getting backed up and have no place to go, the BOV sends it all out of the system. So the turbo is still pushing the same amount of air, but instead of it going into the engine, it is being vented out of the BOV. So nothing hits the throttle plate, so no compressor surge!

 

[Ðawg]

Yea, let me explain why (then you will understand and believe us ). Ok normally, the air goes through the turbo, and into the IC and then the throttle body. Smooth flow, no resistance, its all good. But then, you shift! So, you let off the gas, and the throttle plate slams shut. Now, the compressor wheel (in the turbo) is still pushing that air really hard, but the air is hitting the throttle plate! This extreme force (15PSi or more of air being pushed into a "wall") sends a shock through the whole intake system, back to the compressor wheel. This is called compressor surge. Now if this happens a couple times its okay, but it will start to take its toll on the compressor wheel.

So the BOV comes into play. When you let off the gas, the throttle plate slams shut, but instead of that air getting backed up and have no place to go, the BOV sends it all out of the system. So the turbo is still pushing the same amount of air, but instead of it going into the engine, it is being vented out of the BOV. So nothing hits the throttle plate, so no compressor surge!

Damn good post. Easy to read and understand.

--Scott

 

[Chuck_3]

Agreed! good clarification

 

[Defiant]

So the BOV comes into play. When you let off the gas, the throttle plate slams shut, but instead of that air getting backed up and have no place to go, the BOV sends it all out of the system. So the turbo is still pushing the same amount of air, but instead of it going into the engine, it is being vented out of the BOV. So nothing hits the throttle plate, so no compressor surge!

Ah... nearly.

It vents out if you aren't recirulating. If you are recirculating (as your ECU wants you to), instead of venting it out, it runs it back to the intake side of the compressor and just loops. It kind of lets the compressor coast without doing anything, including speed and boost. There's some suspicion that it even helps the compressor retain speed because of the force of the air coming into the blade, but I'm leery of that being true (the compressor turbine blades just aren't shaped to capture incoming air).

To see what a turbocharger is going through without a BOV, put your hand against the outlet of a vacuum cleaner such as a shop vac. As the blades are unable to exhaust the air they're drawing in, you'll hear them stall as the drive motor goes wild.

 

[SpeedFreak03]

About the venting and recirc thing, I was tryin' to keep it simple. But it still basically does the same thing

 

[philipkrotch]

well what about starions...they dont have a bov.

 

[SpeedFreak03]

But how much boost do they run (stock)? And why do you think you don't see many of those anymore jk. Anyway, a lot of turbo'ed hondas don't use BOVs, because they only run 6-8HP (because of their high-compression motors). 6-8PSi of air hitting a throttle plate won't hurt it as much as 11-12PSi (DSM).

 

[prostreetdsmx1]

you know this is a really interesting debate because signal, kei office and the D1 drift cars have no BOV. The D1 cars run whats called a v-mount intercooler setup, where as the radiator is angled back about 30degree's and the intercooler is mounted horizontally between the motor and the front end and the piping on the IC is less than 2ft. they run no BOV and what you hear on drift videos is the air sucking back into the compressor wheel. They claim that spool up is faster (ideal for drift cars) and it holds boost without having to worry about a BOV leak. now keep in mind a drift car running anything larger than a td0518g is quite rare so maybe its just something they can get away with, with the smaller turbo. We have setup a few of these competition cars that we run and i will say the turbo is quite responsive and the turbo's seem to be holding up. We'll see how they end up in the long run.

just food for thought.....

 

[philipkrotch]

you know this is a really interesting debate because signal, kei office and the D1 drift cars have no BOV. The D1 cars run whats called a v-mount intercooler setup, where as the radiator is angled back about 30degree's and the intercooler is mounted horizontally between the motor and the front end and the piping on the IC is less than 2ft. they run no BOV and what you hear on drift videos is the air sucking back into the compressor wheel. They claim that spool up is faster (ideal for drift cars) and it holds boost without having to worry about a BOV leak. now keep in mind a drift car running anything larger than a td0518g is quite rare so maybe its just something they can get away with, with the smaller turbo. We have setup a few of these competition cars that we run and i will say the turbo is quite responsive and the turbo's seem to be holding up. We'll see how they end up in the long run.

just food for thought.....

ya, i was talking to one of the guys driving the falken silvia at a drift competetion near where i live and i noticed it had no bov. i questioned it and he said that spool up time is sooo much quicker, almost instant and that it doesnt really affect anything because the the turbos the drifters use are never really big . he had a bigt28 i believe, and he said its been lik ethat for 3 seasons now with no problems, and NO shaftplay. i found it kind of interesting.

 

[boostedinaz]

you know this is a really interesting debate because signal, kei office and the D1 drift cars have no BOV. The D1 cars run whats called a v-mount intercooler setup, where as the radiator is angled back about 30degree's and the intercooler is mounted horizontally between the motor and the front end and the piping on the IC is less than 2ft. they run no BOV and what you hear on drift videos is the air sucking back into the compressor wheel. They claim that spool up is faster (ideal for drift cars) and it holds boost without having to worry about a BOV leak. now keep in mind a drift car running anything larger than a td0518g is quite rare so maybe its just something they can get away with, with the smaller turbo. We have setup a few of these competition cars that we run and i will say the turbo is quite responsive and the turbo's seem to be holding up. We'll see how they end up in the long run.

just food for thought.....

I dont see how the position of the IC will affect if the car needs a BOV or not. Perhaps a better explanation of this setup would be ideal.

Why not just run a BOV setup like our cars??? They have the ability to relieve pressure and when the shift is made it purges the air into the compressor to help spool up. The best of both worlds. As far as spool up, I dont see how not having a BOV would help. As long as the BOV wasnt open the turbo should spool just the same. With no BOV there is no way to route the air back into the intake and keep the wheel spinning, so in theory it should slow the wheel down when that air crashes into it.

Perhaps pics or a detailed explanation is in order.

Michael

 

[crankbender]

there is 1 thing missing in this discussion which will help people understand a little better.

When the air slammes into the TB and backs up it creates a pressure wave which then travels back down the intake and slammes into the compressor blades. Then all the air tries to flow back out the compressor. In no way can this help spool-up. In no way can this be considered good for the turbo. It is just all around a bad idea.

Air is just a fluid think of you holding a fan spinning at 150,000 RPMs and getting hit by a wave. Thats what happens when you don't use a BOV and it is just a matter of time before you bend something and the turbo doesn't work as well (may only be minor but it happens for sure).

 

[prostreetdsmx1]

I dont see how the position of the IC will affect if the car needs a BOV or not. Perhaps a better explanation of this setup would be ideal.

Why not just run a BOV setup like our cars??? They have the ability to relieve pressure and when the shift is made it purges the air into the compressor to help spool up. The best of both worlds. As far as spool up, I dont see how not having a BOV would help. As long as the BOV wasnt open the turbo should spool just the same. With no BOV there is no way to route the air back into the intake and keep the wheel spinning, so in theory it should slow the wheel down when that air crashes into it.

Perhaps pics or a detailed explanation is in order.

Michael

I didnt say that it is a better way to go, from what i was told by the Signal Rep is that the reason for no BOV is because boost is retained better because the "hotpipe" as they call it (uicp to us) is still charged so when they get on it after shifting its like instantanious boost add to that the fact that piping is less than 12" and you have a spool up that is unbeatable!!!!!!!!! Also in drift events there is very little shiftin but alot of on and off of the throttle, instant boost is key for drifting which is also why they run small high spooling turbo's, for example on the car we compete with is powered by a SR20DET and spools a Ball Bearing t-28 and hits full spool at 2700 (17psi). Many japanese companies seem to feel the same way because there are like 3-4 kits out there in the same setup. Hope this helps to understand better. We are currently testing a similar setup we made on a 240 and we are waiting to see how it does, i'll keep you updated on any progress.



Example:

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This is Chunky Bai's Car. This is a Signal car and they make the intercooler kit that is desgined with no BOV.

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[boostedinaz]

I didnt say that it is a better way to go, from what i was told by the Signal Rep is that the reason for no BOV is because boost is retained better because the "hotpipe" as they call it (uicp to us) is still charged so when they get on it after shifting its like instantanious boost add to that the fact that piping is less than 12" and you have a spool up that is unbeatable!!!!!!!!! Also in drift events there is very little shiftin but alot of on and off of the throttle, instant boost is key for drifting which is also why they run small high spooling turbo's, for example on the car we compete with is powered by a SR20DET and spools a Ball Bearing t-28 and hits full spool at 2700 (17psi). Many japanese companies seem to feel the same way because there are like 3-4 kits out there in the same setup. Hope this helps to understand better. We are currently testing a similar setup we made on a 240 and we are waiting to see how it does, i'll keep you updated on any progress.

I could see the idea in my head and the pics just verified it, but the air, no matter were it is, or what pipe it is in it will still crash into the compressor wheel and slow it down. There is no way to get around that it is just physics. The shorter piping and its placment wont let air re-route into the comp. wheel. I still fail to see an explanation for why that "works"

Michael

 

[jt1583]

I think hes saying that when you let off the gas and the bov opens the pressure inside the intake is going to be close to atmospheric ( less boost). but with no bov the pressure in the intake is normal boosting level if not higher due to the closed throttle plate. so when you get back on the gas and open the throttle that compressed air in the intake is ready to go into the engine and you dont need to wait to spool again. this seems like it would cause quicker spool up other than the air hitting the compressor factor. but if these d1 drifters are doing it then it must be atleast an idea to look into.

 

[prostreetdsmx1]

I think hes saying that when you let off the gas and the bov opens the pressure inside the intake is going to be close to atmospheric ( less boost). but with no bov the pressure in the intake is normal boosting level if not higher due to the closed throttle plate. so when you get back on the gas and open the throttle that compressed air in the intake is ready to go into the engine and you dont need to wait to spool again. this seems like it would cause quicker spool up other than the air hitting the compressor factor. but if these d1 drifters are doing it then it must be atleast an idea to look into.

thats the basic principle. i wouldnt say that just because they do it makes it right, i am simply sayin what is used in that market and what is used by the top dogs, on ours, we have it plumbed almost exactly like the signal kit so we are waiting to see how it works i will say it spools amazingly fast and in the 2 months we have had it on the car we have seen not 1 negative result.

 

[boostedinaz]

thats the basic principle. i wouldnt say that just because they do it makes it right, i am simply sayin what is used in that market and what is used by the top dogs, on ours, we have it plumbed almost exactly like the signal kit so we are waiting to see how it works i will say it spools amazingly fast and in the 2 months we have had it on the car we have seen not 1 negative result.

So you dont here any compressor surge at all??

When these cars go on and off throttle then it will build up pressure, yes, but it will also force the pressure into the blades slowing them down. Even though the intake will have a bit more air in it you still have to get the turbo spooled again to do the rest of the filling. I still fail to see how this "helps" the turbo to spool. I see no good comming from it. If someone could explain this with maybe some physics to to back it up, them I can see maybe agreeing with it.

Michael

 

[paranoidTSi]

Well I know the Neon SRT4s do not have a blow off valve as far as I was told. I don't think its needed in some cars, but since ours comes stock with one I would recommend it. I don't think you are going to gain much performance taking out a blow off valve, just quicker turbo death. I think the Turbo life is more important than a little bit of performance.

 

[boostedinaz]

Well I know the Neon SRT4s do not have a blow off valve as far as I was told. I don't think its needed in some cars, but since ours comes stock with one I would recommend it. I don't think you are going to gain much performance taking out a blow off valve, just quicker turbo death. I think the Turbo life is more important than a little bit of performance.

Cars themselves aren't needed, but they are a good idea and are useful. Same with a BOV. It is just a good measure to ensure reliablitly over time. Perhaps people that build race cars arent worried about it becasue the cars see limited driving time, however after 100,000 miles worth of shifts and possible compressor surge I think it would be a useful idea.

Here is you info for the SRT4 BOV.

http://www.agpturbo.com/customer/product.php?productid=7&cat=