What's up with the twin BOV's?

[Guest JAMIE T]

I keep seeing twin bovs for rb26's. Is that needed on a 600whp set-up? I have a greddy Type R BOV now that came with the engine I got from Stony. Will that be enough for 20+ psi? The ones I'm seeing appear to be bolt-on's for the factory set-up. I've heard of twin bovs of very high hp drag cars.

[Guest Battle Pope]

Usually on high horsepower applications I've heard it's a good idea to run a bov for each turbo.

[Vintage-TechZ]

I keep seeing twin bovs for rb26's. Is that needed on a 600whp set-up? I have a greddy Type R BOV now that came with the engine I got from Stony. Will that be enough for 20+ psi? The ones I'm seeing appear to be bolt-on's for the factory set-up. I've heard of twin bovs of very high hp drag cars.

 

Jamie I would say that MAtt @ Motorworx could safely answer that question. I posed the same query when I bought my BCNR RB-26 from Bernard in Japan as it came with factory twin BOV's in series too.

I would imagine they are failsafe back-ups for the higher RPM discharges and perhaps were cheap because they had a milliion made up.

My thought is to go with the two Tial 50mm red ones I bought and mount them as close to the turbos as possible for the fastest hot air discharge......that way I'm not overworking the Intercooler with air that I don't use.

One on each T-discharge tube before they reach or blend to the I/C.

..........Ramble over,Vinny 8)

[240Z_Master]

Related Question...

 

Would it be better to mount the BOV before the intercooler or after the intercooler?

[Guest JAMIE T]

I've heard differant things. I think the ideal location is near the throttle since that is were the restriction happens that cuases the air to need to be removed from the intake tract. It's hard for me to explain. As the throttle slams closed, the air has to go somewere. Releasing it just before the throttle will allow it to vent right away, instead of having to go all the way back to the turbo. Hope that makes sense.

[240Z_Master]

I've heard differant things. I think the ideal location is near the throttle since that is were the restriction happens that cuases the air to need to be removed from the intake tract. It's hard for me to explain. As the throttle slams closed, the air has to go somewere. Releasing it just before the throttle will allow it to vent right away, instead of having to go all the way back to the turbo. Hope that makes sense.

 

That's what I was thinking...like this guy's swap (sorry if I forgot your name!)

[240Z Turbo]

a single Tial 50mm BOV will work fine.

[cheftrd]

Any single large BOV like the GReddy R or Tial 50 mm will work fine. The 50mm valves will pass more air than the two stock ones. There is not a BOV for each turbo, BTW. A single outlet from the surge tank inlet pipe dumps to a common plenum to the two valves, and they discharge into a single return pipe that splits and re-enters the suction pipes between the AFM's and the turbos. It's a common BOV found on other cars and I believe they use two instead of redesigning a larger one; mass produced parts are cheaper.

 

The BOV should be placed as close to the throttle(s) as you can get it. This keeps air moving in the direction of the intake when the throttle is closed. When mounted close to the turbo, the air in the pipe has to reverse direction when you lift, then reverse direction again when you come back on throttle. This causes a little more lag after the upshift. Either way is bennificial for the life of the turbo. Many BOV's that are placed by the turbo are because of packaging restrictions.

 

Along this same line of thinking, I also run the wastegate and actuating port to a pressure/vacuum port like the one used for the BOV. When you lift, it pulls the gate shut, keeping the exh. gasses on the turbine, and opens the BOV, giving the air somewhere to go. This makes for awesome boost response between shifts.

[Guest JAMIE T]

Cool, I've got the greddy R BOV, so I'm good. Thanks guys.

[Vintage-TechZ]

The BOV should be placed as close to the throttle(s) as you can get it. This keeps air moving in the direction of the intake when the throttle is closed. When mounted close to the turbo' date=' the air in the pipe has to reverse direction when you lift, then reverse direction again when you come back on throttle. This causes a little more lag after the upshift. Either way is bennificial for the life of the turbo. Many BOV's that are placed by the turbo are because of packaging restrictions.

.[/quote']

 

Wait a minute .....Correct me if you feel I'm wrong here but...."pressure seeks the path of least resistance",it doesent "KNOW" or "RECOGNIZE" direction of flow. The BOV's serve first to "VENT" at the precise moment the throttle plate reduces or closes.The air in the pipe is at that second "DEAD HEADED" until pressure is again raised by boost and the throttle plate is of course open.

Packaging space requirements I would think ..cause placement of the BOV/s more often than real science.SO ...I would tend to believe venting "PRE-Intercooler" rather than "pre-throttle plate" would more greatly serve the greater good of the "SYSTEM" by not introducing HOT air into the I.C. that it would simply vent down line and not efficiently use !The air is dead at the throttle plate whether it vents one inch from it or one inch from the turbos discharge pipe.Think of the air in the pipes as if it were hydrolic water. Valve open...movement.Valve closed...no movement.

So you either choose to overwork your IC......or you choose to keep your turbo bearings unhammered and your IC as cool as possible at the same time.Its a no brainer to me,some still argue the point.

Sorry for the Highjack.............Vinny 8)

[Guest PROJECTRB240SX]

Actually Optimally You'd Want One Close To The Turbo And Close To The Throttle Body.... This Takes The Pressure Off The Throttle Plate And Reduces Midshift Ic Temps. Its Also Clears The System More Effectively So There Is Little To No Reversion. We Did This On My Rb20 With Great Results And You'll Actually Notice More Power, Only Down Side Is You Now Have Two Weak Links In The Intake Tract Rather Than One.

 

On The Stock Rb26dett's The Two Recirculating Valves Are For Quicker Operation (SAME CONCEPT AS TWO VALVES FLOW MORE THAN ONE LARGE ONE) And Optimum Power.

[Vintage-TechZ]

Actually Optimally You'd Want One Close To The Turbo And one Close To The Throttle Body.... This Takes The Pressure Off The Throttle Plate And Reduces Midshift Ic Temps. Its Also Clears The System More Effectively So There Is Little To No Reversion.

 

 

I agree,somewhat.lol. But once there is closure at the T-plate,thats it....no more movement forward,period.However the turbo is still spooling,pushing the pressure up but with great restriction thus the bearings getting abused. So by placing the BOV after the turbo but before the IC,the cooled dense air in the IC,which is stalled and waiting will still be at relative temps to the last gulp that just passed into the throttle pasage !No temp change (adversly,anyway) so no fuel/air stumble....just instant "back-on" burn. Right ?

Oh well, I've got two 50mm Tial BOV's.......so I'll put one after the turbo and before the IC.........see how it does,then just for curiosity,I'll place another one in front of the T-plate.Then viceversa so I'll know if one works better than the other or if the seperated pair works best in unison.

This combo is going on my RB26DETT AWD Z,so I don't care how the plumbing looks,I just want max efficiency and light weight........consistant,denser,cooler air are my friends.

...............Vinny 8)

[Guest PROJECTRB240SX]

good luck and please do report your findings..... I do know it worked better on my rb20det which is why I kept that setup and it was setup along with bigger intake tubing which could be an additional factor but I belive it would be the same results.

 

please do post your findings as it would be beneficial to alot of people here and very relavant to what most the turbo members here are trying to achieve.

[cheftrd]

Any fluid (air is a fluid) moves from high pressure to low pressure. When the throttle closes, the pressure in the pipe spikes. If the BOV is next to the turbo, the pressure drops there first. The high pressure at the throttle then tries to go where there is less pressure (the turbo), reversing flow. When you hit the acceleerator again, the air must then reverse flow again. Compressor surge (whoop whoop whoop) is just that, airflow reversed. The difference is that it tries to go out the compressor inlet instead of the BOV and stalls the compressor. The main performance reason behind using the BOV is the fact that the lag time after an off throttle shift is less, due to the compressor not being stalled.

 

I understand what you're trying to say about water, but it's different in that a fluid with the viscosity of water (liquid) is uncompressable. When a relief valve is opened in a closed, pressurized pipe containing water, there is NO FLOW because you can not have more water than the volume of the pipe. The pressure in the pipe decreases at the same rate everywhere in the plumbing at the same time. Air, on the other hand, is compressable, and we can have more than the volume of the pipe in the pipe. When the valve is opened, the pressureized air will flow to the area with less pressure (ambient outside). The cooling effect of cooler air going back into the intercooler vs. hot air that has to go into the intercooler anyway, is insignificant compared to keeping the air flowing in the correct direction concerning acceleration.

 

This applies to a manual transmision vehicle that has the clutch released and trailing throttle between shifts. If you hold it to the floor for an entire quarter, where the BOV is makes no difference.

[Vintage-TechZ]

If the BOV is next to the turbo' date=' the pressure drops there first. The high pressure at the throttle then tries to go where there is less pressure (the turbo), reversing flow. When you hit the acceleerator again, the air must then reverse flow again. Compressor surge (whoop whoop whoop) is just that, airflow reversed. The difference is that it tries to go out the compressor inlet instead of the BOV and stalls the compressor. The main performance reason behind using the BOV is the fact that the lag time after an off throttle shift is less, due to the compressor not being stalled.

 

The cooling effect of cooler air going back into the intercooler vs. hot air that has to go into the intercooler anyway, is insignificant compared to keeping the air flowing in the correct direction concerning acceleration.

[/quote']

 

The amount of air surging out of any given BOV under use is ,I agree, is "insignificant" compared to overall flow through the pipe after compression.

What I have a hard time grasping is .......a compressor wheel spinning 33,000rpm-100,???rpm in VERY close tolerances of housing ,is ever going to STOP abruptly and allow air flow to REVERSE.

Now I'll concede that the wheel can be AFFECTED by being "DEAD HEADED" by the affects of the throttle plate slamming closed......even perhaps turning that energy into vibration/shudder (the sound it makes)(death by harmonics to the bearings)( also tolerances of the bearings being affected by thrust)........but to actually direct air backward through those super tight tolerances while the turbine is still motivating the shaft that also spools the compressor wheel just is hard to digest without question.Even though your (at that moment) under deceleration....the blades are still spinning at a high rpm.

Back to path of least resistance........as long as the increasing pressure from the turbo is pushing into the discharge pipe,the "pressure" at that area is "Greatest".Therefore finding its way out of the nearest BOV places the air traveling there while holding steady the overall system pressure(all the way to the Throttle plate.)

Once your back into the gas pedal and the impellar blades increase velocity/Speed/rpm and begin to raise the CFM in the pipe, the flow as your referring to it,will once agin motivate to the "path of least resistance" once more. Only this time, its' not through the BOV ports.

Now I know none of us really care about this enough to perhaps to go on.......so I'd like to say upfront, thanks for putting up with my mummbles ! lol

Matt....you know once I get to drive that AWD RB, I won't be mummbling about issues/concerns like this ? I'm normally not a "HAIR SPLITTER",so my apologies if my points are .........moot.

...........Vinny 8)

[cheftrd]

When I was talking about surge, I meant a system with no BOV. I should have been more specific. Where there is no BOV, the high pressure air has nowhere to go but back out the turbo. On super high boost apps. with no BOV, I've seen the shaft twist in two, wheels slip on the shaft, and compressor nuts come off (Mitsubishi). closing the throttle on 30 psi at 80 lb/min can cause a 100+ psi spike. No apologies necessary. Always question everything, especially that what you read on an internet forum.

[Ed260Z]

I wanted to add a few comments to this old thread.

 

A BOV is deffinatly a neccesity when it comes to turbo charged motors. But should they be recirculated back to the turbos intake? Sure your going to loose the "cool" sound, but won't it help your turbo/s spool back up faster.

[savageskaterkid]

From experiance with a supra, it won't make you spool faster, but it will keep your car from running rich for that split second between shifts. If you rev the engine up a bit and get the turbo boosting about about 6 psi, then shift(with an Aftermarket BOV) and not slam on the gas again, it will run rich and tends to cut off-It happens all the time, idk if its any diffrent on any other car. The boost is recirculated b4 the throttle plate, not b4 the trubo.

[Ed260Z]

The boost is recirculated b4 the throttle plate, not b4 the trubo.

 

I thought that you would put the BOV or Recirc valve before the throttle plate, and then route the extra air in front of the turbo.

[mario_82_ZXT]

About things talked about earlier on the thread, a lot of turbo dodge guy's run the BOV on the hot pipe before the IC. That's how I have mine on my ZX with no ill effect. I have the RFL and its a lot a fun to set off, but I wish it had the high pitched wistle some of the bov's have.

 

On the thing about the recirc, I think it has to be plumbed pre-turbo and be directed at the turbine or something.

 

On running rich, that usually happens on AFM and MAF systems. I have MS, which is map based and I don't run into the problem. On the stock turbo ECU people generally have a black cloud exit when they shift or the car falls on its face.

 

Mario