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Compressor Valves: BOV/DV/Radial R35/R55 (29)

Category: Blow Off Valve

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What are the dimensions of the Synchronic BOV?


The dimensions of the Synchronic BOV can be seen in the attached drawing.

Inches are represented in brackets, milimeters are represented below that.  Each measurement is accurate to +- 1 of the last digit.

Download PDF Datasheet: SB Packaging.pdf (30.01 KB)
Please note you will need the free Adobe Reader™ to view this file.

What improvements have been made to the Synchronic BOV?


Improvements to the design are the following:

Elimination of port C on the side of the BOV-  This port is now internally ported on the design and is the hallmark of the latest revision.  Performance of the BOV & it's ~17 millisecond initial response time remain unchanged.  The original design with an external port C was made public in case there would be the occasional application that required the boost-only source to be plumbed before the intercooler to make use of the pressure difference that may (or may not) exist before and after the intercooler.  We have always had our own units internally ported for simplicity and have rigorously tested & validated this change for over 3 years.  We will still have the original design in limited quantities and available only for special orders and industrial applications.  We believe that the benefits in having one less connection to plumb (or fail) far outweighed the 1% of users out there that needed the externally ported design.  

Port C BOV

Port C Eliminated BOV

Change to 1/8th NPT threaded vacuum ports-  This design change has eliminated the use of the small M4 brass fittings.  Although the initial design was compact and very light weight, we received enough feedback that prompted the change.  We want to show that we do, in fact, listen to customer feedback, take it very seriously, and will only make a change after significant testing.  With this change, you will no longer be able to over tighten and break brass fittings.  You can also use our boost-connect fittings, which includes a 90 degree fitting for use in very tight installations.  You should also know that this new back cap design is backwards compatible with even the very first Synchronic BOV released to market.  You can upgrade your Synchronic BOV to this latest back cap using kit # SB001A.KIT022.

1/8npt 1 touch pneumatic fittings

1/8npt upgrade kit (SB001A.KIT022)

Old Brass fitting vs. 1/8npt vs. 1-touch pneumatic Boost Connect fitting

M4 mounting bolts- The mounting bolts have now been changed over from M4 set screws to M4 bolts to give users the ability to apply more force when tightening down the BOV on mounting flanges.

New mounting flange geometry- This new design eliminates any chance of o-rings getting damaged upon installation.

All of the universal Synchronic BOVs & application specific kits available in the market today should include all of the improvements above.


What is a Port C delete and what is the service procedure?


Port C refers to the chamber behind the piston acuator. In previous generations of the Synchronic BOV port C was an independent chamber that needed an uninterupted boost signal to function properly.

Pressure flows in from the side port and pushes against the piston, this equalizes the pressure in both the inlet chamber and acuator chamber


In newer generations of the Synchronic BOV we have eliminated the need for an independent port C fitting.

If there is no port C on the side of your valve you have the newest version of BOV. Earlier versions with Port C deleted had a hex cap bolt installed on the side of the valve to seal off where port C used to be.

Port C delete service requires complete disassembly of the BOV to port the casting so the C chamber can receive it's pressure signal from the BOV inlet chamber.

Here you can see the internal port C.


If the Synchronic BOV you have purchased does not have a port C, then you have purchased the newest revision of the Synchronic BOV. The newest revision of the BOV has port C internally built in, therefore the installer no longer has to spend extensive time sourcing a boost only source for port C. 
The functionality of both versions of the BOV is identical. 
Can older Synapse BOV (those still have port C) be converted to internal boost feed?
Yes, we offer this port C delete service to those whom have the older version of the Synchronic BOV, and wish to update their BOV to the latest revision. The procedure is listed below:
Go to www.synapseengineering.com/support and start a service ticket record. 
Fill out the form in this link for the port C delete service, and then print it out.
The user must send in their BOV, the completed service form, and include a self addressed UPS or USPS return shipping label for sending the product back. 
The Service fee is $35.00. You may send the payment via PayPal to: info@synapseengineering.com. If you wish to pay for the service via credit card, please contact our tech support department directly at +1 (858) 457-1700.
The service turn around time is 5 to 7 days from the day our service department receives the package. Your online ticket record will be updated accordingly to help you track the progress.  

What is causing my Anti-Stall Kit leak?


The Synchronic BOV is designed to be open under low load conditions. The Anti-Stall kit is designed to prevent unmeasured air from being sucked in, or metered air being blown out of the engine.  If you are running an efficient turbo, the charge pipe pressure may be higher than the spring keeping the anti-stall kit sealed, and is causing the excess air to be blown out of the BOV. While the intake manifold is under boost, the valve is closed and will not open again until the intake manifold pressure drops. We highly recommend re-circulating the BOV discharge back into the intake piping before the turbo, and after the MAF sensor.




What is the Anti-Stall Kit and how to properly install it?


The Anti-Stall kit is designed for those who have Mass Air Flow equiped forced induction vehicles and want to use the Synchronic BOV to vent to atmosphere instead of re-circulating the discharged air. 

The Anti-Stall Kit is a cap that fits over the discharge of the BOV.  The cap is attached to the BOV by a long screw and a spring.  When the BOV discharges, it will blow the cap open and release the discharge air.  When the BOV has finished discharging the air, the spring will pull the cap shut, hence the BOV will not be blowing out  metered air and causing the MAF car to stall or  idle rough.

The kit comes with the following parts and should be installed in this order:

Bolt -> Spring -> Washer -> O-ring -> Anti Stall Cap 


Do not over tighten the bolt onto the valve as it may cause heavy load on the spring and preventing the cap to properly open during discharge.


***It is recommended to always re-circulate the BOV discharge air for best vehicle performance and drivability.***


What is the BOV upgrade kit, and what does it include?


The BOV upgrade kit consists of a new redesigned back cap with sturdier 1/8th NPT threads, two types of  push to connect fittings, one push to connect Y, and 5 ft of black PU hose. This upgrade kit is available through our storefront as Kit: SB001A.KIT022.


What is the design philosophy behind the Synchronic Blow-Off valve


by Peter Medina

When I designed Synchronic BOV, I really wasn't thinking about trying to outdo every BOV design on the market.  In fact, just 1 year prior, I was granted the patent on the technology behind the Synchronic geometry.  My goal, was first to see how this geometry would apply to a BOV, considering that it works completely different from my previous application of the geometry to a rising rate fuel pressure regulator.

So whenever you design product, you have to have some design goals.  Or what design engineers like to call, design intent.  My 3 primary goals were:

1)  Design a BOV that would absolutely NOT LEAK boost
2)  Design a BOV that would actuate very fast
3)  Design a BOV that would stay shut under high vacuum (to be discussed later)

Problem #1: Design a BOV that would absolutely not leak boost Once I started to work on the geometry in 3D CAD, I knew that I had to design a pull-type valve that seated harder as boost increased in the intercooler pipe.  I also started to understand where the Synchronic geometry fit in.  I knew that I could address #1 by using the different surface areas of Synchronic in order to have surface areas exposed to system boost pressure that mathematically would not allow the valve to move in any direction, under boost, except to close the valve to the seat.  This is where Port A and Port B  www.synapseengineering.com/pdf/bov-manual.pdf fall in relation to the valve area of the BOV.  Applying  the same system pressure to Port A and Port B at the same time as there being boost pressure in the intercooler pipe, coupled with spring pre-load pressure meant that mathematically, there was no way for Synchronic's valve to open.  Now the valve not opening doesn't mean that it won't leak  Undecided  Many BOVs out there don't leak because their valves open.  In fact, they should, theoretically, not leak either.  But where most designs fail is in their sealing mechanism.  The best seals are not statically pressed pieces that try to hold off pressure from getting by.  instead, they are dynamically moving mechanisms that actively react to changes in pressure to seal them off.  Which is why I decided to engineer proper o-ring glands, especially at the dynamic valve head that would move in relation to the sealing surface I designed.  Other designs go the easy route by using rubber overmolded washers like those used in window seals in your house instead of a properly engineered sealing gland, like those used in aerospace.

Problem #2: Design a BOV that would actuate very fast    I already knew that simply eliminating the diaphragm in the design would increase the response time of the valve by eliminating the time required to stretch the diaphragm when the actuating pressure came in to pull the valve open.  

But would  you believe that the Synchronic geometry itself has plenty to do with a fast acting valve?  You see, a piston alone doesn't mean that you have a stable valve actuating mechanism.  If you only have 1 plane of support with 1 o-ring tier, you still have rocking of the piston back and forth, and the same goes with adding o-rings of the same diameter.  What Synchronic geometry offered were 3 tiers of o-rings on 3 different diameters.  That meant a very stable actuating mechanism when you actually wanted it to pull the valve quickly.  Even though there was added friction, the design eliminated noise in actuation.  On top of that, the 3 tiers generated 4 pressure chambers.


In a normal single tier actuator design, you only have 2 surface areas that pressure works upon.  The top and bottom of the actuator surface on either side of the o-ring.  In the Synchronic design, you actually have pressure working on cylinder surfaces that self center the actuator when it is pressurized which leads to a more stable actuation.  And even though you leave some of those chambers to atmosphere, you have to remember that atmoshperic pressure is still pressure.  And as the piston collapses that chamber, the air that was in the chamber is exhausting out the port at a rate that follows the movement of the piston and acts on all surfaces within the chamber.  

Now, the thing with most push-type BOVs is that pressure in the intercooler pipe helps push them open when vacuum pulls the actuator up.  Since Synchronic BOV is a pull-type,  this means that as boost pressure increases, the harder that valve seats to seal off boost.  This is why there is Port C.  I designed the surface area of Port C to be just the right ratio to either Port A, Port B or Port A & B so that when boost-only pressure is applied to Port C, it will either open at a high boost pressure, or not open at all.  But what Port C does is that it equalizes the pressure on either side of the piston so that no matter how much boost you run, 5, 10, 20, 50, 150 psi of boost.  There will always be the same amount of force required to open the BOV when you close the throttle.  You have to remember that no matter how much boost you run, whether it is 5 or 150 psi.  When you shut the throttle, you'll always have the same 20-26" of vacuum!

Listen to the throttle action at the end of the video (1:02) to hear just how responsive Synchronic BOV is: 



Problem #3: Design a BOV that would stay shut under high vacuum  Something told me not to worry about this too much until later.  When I first started to test the prototypes of the design, I couldn't get the valve to stay shut under heavy vacuum.  When it would be shut at idle, the BOV wouldn't open.  And when it would be open at idle, it would work perfectly between gears.  I kept fighting it and fighting it, until I finally gave up and conceded to the design.  Little did I know later that this was one of those discoveries of serendipity.  Beta testers began to report better throttle response.  What?  I started to look at how that worked and, guess what?  It makes sense.  By bypassing the restriction of the turbo, intercooler piping and all the surface area of the intercooler, you do get better throttle response when coming off of vacuum.  And they also started to report better fuel economy.  Huh?  So testing on the dyno started to show that cars were able to hold the same RPM and wheel speed with less horsepower and torque.  So this just isn't a "defective" feature to fight, but instead embrace.  Instead of going for the ricer noise that we all secretly long for, we need instead to re-circulate the BOV inlet/discharge and run a cone filter to get the noise.

The simple answer to the question above, is of course it can!

In the world of blow-off valves, Diverter Valves, Dump Valves, Dump Ventils, etc.  It needs to be understood that there are many people playing the "me too" game.  If you don't have an original approach to solving the problem ( Huh compressor surge?), or even know how to identify it ( Huh compressor surge?), then you tend to try to outdo the other guy in the one parameter that everyone else is competing on.  

Flow, to a certain extent, is merely a band-aid in eliminating compressor surge. If you don't have a fast enough actuating mechanism to get rid of surge, flow will mask that.

Compressor surge happens this way:  Turbo is spinning many thousands of RPMs at engine WOT (wide open throttle) -> throttle shuts-> pressure builds up between closed throttle and still spinning compressor wheel -> pressure has to go somewhere so it stops the spinning compressor momentarily to pass air over and over again -> So you hear tsssch tsssch tsssch tsssch -> each successive tsssch is air passing the compressor wheel out the inlet of the turbo in the other direction from where it is supposed to go -> Turbo slows down and stress is put on the common shaft because you have to remember that the exhaust is still torquing the turbine wheel to spin the compressor.

Well, the Synapse approach isn't to make the biggest flowing BOV on the planet with the biggest flow hole on the front of it.  Why?  Because the goal IS NOT to dump all of the air that your turbo just worked so hard to make, just so that it can build it all back up in the next gear. The goal of Synchronic is to clip the pressure rise in the intercooler pipe as soon as the throttle closes so that the pressure rise doesn't happen at all.    It does this by following actuating the BOV to do exactly what is going on behind the throttle plate.  Watch Synchronic BOV in this video follow the throttle action, only milliseconds behind:



Many other manufacturers make the mistake of chasing higher flow rates on their BOVs simply because their designs can't actuate fast enough.  What good are high flow rates when the turbo is flutterdumping?  Let me define flutterdump.  Flutterdump is when the compressor surges, then dumps the air seconds later to get rid of the surge.  The goal is to eliminate compressor surge, not just delay it.  The goal also is not to have a BOV that makes the turbo surge below a certain boost level, only to work at higher boost pressures.  This is a design flaw whose goal is for the BOV to stay shut at idle instead of ridding the system of compressor surge.  That is why those designs have you selecting springs based on your idle vacuum level, because all they care about is staying shut at those idle levels.  The thing you have to remember as a street user is that you are not running max boost all of the time.  To the contrary, in every gear you are probably making less than 4 -6 psi of boost.  Compressor surge at 95% the life of your turbo is not acceptable.  And for the racer, compressor surge at part throttle, or corner throttle modulation should not be acceptable either when there is a simple solution, Synchronic BOV.

Can Synchronic BOV flow enough?  Here's 1,000 reasons on Methanol to tell you that 1 Synchronic BOV alone is enough to address 30+ psi of boost.  Listen closely, there is not one hint of surge in Maztech's video:



Why are the brass fittings for the signal ports not able to be screwed down completely?


The brass fittings provided in the SB and DV series are the correct size for the SB/DV.  The brass fitting should be screwed down to about half way or slightly over, but not completely down.  Torquing the brass fittings completely down to the bottom may cause damage to the BOV/DV unit.  
brass fitting install

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