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

Atom Feed Frequently Asked Questions

Parent Categories

FAQ Home

Sub Categories

Blow Off Valve (18)
Diverter Valve (7)
DV002 (1)
R35 (Radial R35 Valve) (1)
R55 (Radial R55 Valve) (0)

Category: Compressor Valves: BOV/DV/Radial R35/R55

Page 1 of 3 - Previous 1 2 3 Next All Page: Items per page:

Air:Fuel Ratio Changes with Synchronic Valve


If you have a completely stock/OEM turbocharged vehicle, the addition of a Synchronic valve should not have an effect on the system's Air:Fuel Ratio so long as it is properly installed.  

My idle AFR used to be richer with my old BOV, when I installed the Synchronic valve my idle went leaner.  For example 13:1 to 13.5:1.

  • ANSWER: If your old valve was closed at idle, and you've now added the Synchronic valve, which is now open at idle, this could account for a leaner mixture because the open valve unloads the compressor in conditions where the throttle plate is essentially closed, such as idle and cruising.  You can verify this by removing the vacuum signals to the back of the Synchronic valve, capping off the vacuum line and measuring your AFR.
  • ALTERNATIVE SOLUTION: You can adjust your pre-load on the Synchronic valve to close the valve more under idle and light throttle conditions.  However, you need to keep in mind that adding more spring pre-load slows down the valve's reaction time, increasing the likelihood of producing compressor surge or flutter.

Under boost my AFR used to be richer with my old BOV, when I installed the Synchronic valve my idle went leaner.  For example 12:1 to 13:1.

  • Is my BOV leaking?  If your BOV was leaking and you have either an MAF or MAP sensor car, your AFR would actually go very rich if you have a BOV leak because the ECU is still injecting the same amount of fuel for less air mass entering the engine.
  • What is likely happening is that the Synchronic valve has eliminated a boost leak in your system or it allows the system to be more boost efficient than the valve you used to have in the system.  If this is the case, the increase in efficiency tranlates into an increase in engine flow or cylinder pressure which means more horsepower that requires more fuel.  You will need to add fuel to the system by tuning for more fuel enrichment.
    • You can verify this effect by eliminating the valve altogether and capping the mounting location temporarily with something that will be sealed and you will find that the same effect to be true.
  • ALTERNATIVE SOLUTION: If you have the ability to lower the operating boost pressure, you can reduce the boost by 1 psi and you will find that you are likely making the same amount of power at the lower boost level.  This can be a solution until you can get a retune.

Author: PM

Between the R35V, SB, DV and R55, which valve has the most flow rate ?


In order of lowest to greatest flow capacity are the following:

  • DV - Diverter Valve 35 mm - The DV can be recirculated or vented to atmosphere (VTA) and will hold boost at nearly any pressure up to 200 psi.  Flow capability will be limited by the recirculation flange size used (OD) 1", 1.25", 1.375" or 1.5"
  • SB - Synchronic BOV 40 mm - The SB can be recirculated or vented to atmosphere (VTA) and will hold boost at any pressure up to 200 psi. Flow capability will be limited by the recirculation flange size used (OD) 1", 1.25", 1.375" or 1.5"
  • R35V - Radial Trident 35 mm - The R35V is a VTA only valve with a high flow capacity and unique sound signature due to its 3 trident exhaust ports that allow maximum flow capacity
  • R55V - Radial Trident 55 mm - The R55V is a VTA only valve with a high flow capacity and unique sound signature due to its 3 trident exhaust ports that allow maximum flow capacity, this is the valve of choice for high-flow centrifugal supercharger applications

Do I need to re-lube my BOV like the other ones on the market?



Since Synchronic BOV is a piston actuated BOV, the question has come up whether or not it needs servicing with every oil change.  Or perhaps it wears out over time and stops working as well as when it is new.  The piston BOVs and DVs that are out on the market today, unfortunately have generated this false impression about the Synchronic BOV.  

The Synchronic BOV was specifically designed around this problem.  The blue is the valve and the piston is in red (see image below).  As you can clearly see, the piston is located in its own chamber.  The valving mechanism is an actual valve that doesn't require lubricant.  Existing piston designs have the actuating piston in communication with all of the airflow.  So that with each dump of the BOV, there is lubricant in the system that gets discharged with it.  Synchronic BOV does not need to be re-lubed since the actuating chambers retain all of our proprietary lubricant.  The lubricant does not evapaporate or fade over time.

And for those of you that may be wondering about the part of the piston that is exposed to airflow, there is a wiper in the mechanism to save lubricant and that surface gets relubed with each stroke of the piston.



How can I get replacement O-Rings if mine get damaged?


(you should offer an O-Ring kit with at least 2 of each size in the Accessories).

Author: Eric Dunn

How do I fix my partial throttle loss of boost?


During partial throttle conditions the intake manifold has lower pressure than the charge pipe (boost only) sections of the vehicle. Because of this and the way our BOV is designed, the BOV will be open. The only way to fix this is to increase the amount of force acting on the valve to keep it shut. This can be done in two ways.

1) Pneumatically - Decrease the surface area that the intake manifold pressure/vacuum can act on, by switching to port B only, and leaving port A vented to atmosphere.

2) Mechanically - Increase the spring force acting on the internal piston with stiffer springs, or cranking down on the preload adjuster to increase the preload.


How do I make my BOV louder?


To make the BOV louder when running VTA you can:

- Switch to port B vs port A+B.

- Remove the recirculation flange on the end of the BOV.


To make the BOV louder when re-circulating you can:

- Switch to port B vs A+B.


*Note:  Not every car will have the same sound, factors such as boost level, BOV mounting location, IC pipe routing and vehicle tune will have an effect on the audible sound of the BOV discharge.


How do I make my Synchronic valve louder?


The Synchronic Valve was designed as a pure performance product.  That being said, here are some tips.

  • Adjust your pre-load adjuster lower to limit the travel of the valve piston.  The smaller cross sectional area will result in a louder discharge as the air moving through it will be moving faster.  Please loosen the lock nut before adjusting the adjuster.
  • Install a heavier spring.  A heavier spring will have the similar effect of limiting overall valve travel height.  A heavier spring may delay the response/reaction time of the valve resulting in flutter, so it is something you will have to weigh.

Author: PM

I have on-boost flutter that I did not have before, how do I fix it?


On-Boost Flutter is different from flutter that happens when you let off the throttle and the throttle plate closes.  On-Boost Flutter is surge, where the turbo is operating in an unstable area of the turbocharger's compressor map.  A compressor bypass valve such as a Diverter Valve or BOV have nothing to do with how this characteristic happens when the valve is closed.  Either way, the turbo is producing more airflow than the engine can ingest, resulting in backflow through the compressor section of the turbo.  OEM diverter valves have built-in leaks in their valving mechanism as a workaround to surge, the only problem is that the leak exists in all operating conditions, low boost, high boost, etc.  At the end of the day, you will need to unload the compressor in order to eliminate On-Boost Flutter (surge). 

Solutions:  Run a very light spring in the Synchronic device.  This will allow you to leak the boost slightly as boost onset happens and will close the valve completely under WOT or full boost conditions.  This is a necessary solution for some cars (Evo) where part throttle on-boost flutter results in vehicle instability due to varying signals that the MAF is receiving.

How to Test:  You can test if the Synchronic compressor bypass valve (CBV) is the culprit by eliminating it from the equation.  Use a thick piece of rubber, to block off the discharge or inlet port of the CBV so that the system acts as though there isn't a device at all.  If you still have on-boost flutter, then it is a characteristic of your turbo and how it matches up with your engine setup (cams, injectors, fuel, etc.).  Alternatively, you can remove the pre-load adjuster from your CBV and install a bolt down far enough to hold the actuating piston in place and not moving.  This will also have a similar effect.

Why do I have on-boost flutter now, I didn't have it before?:  Environmental conditions have a great effect on whether or not a turbo will surge.  Higher altitudes (elevation) will trigger surge.  You will also have a higher incidence of surge when the air density is increased.  Anecdotally, you will also find that turbos that have more wear on them will also tend to flutter more.  The type of wear will vary and can be anything from an increase in compressor blade tip to housing clearance, all the way to slight bearing wear.



I have on-throttle flutter since installing the Synchronic BOV/DV


On quick spooling turbos on small displacement engines such as Evos, at lower RPMs at high load, the compressor is delivering more air than the engine is able to ingest. The result is turbo flutter. The turbo is spooling and pushing more air than the engine can handle. On compressor maps, this means the engine is operating on the left hand side of the surge/stall line. 

The way the vehicle manufacturers got around this issue was by designing a leak into their factory diverter valves.

When you replace the leaky factory diverter valve with a perfectly sealing Synchronic BOV or DV, suddenly the turbo starts to flutter. The BOV/DV is staying shut while this flutter is happening. By replacing the leaking factory diverter valve, you're not forcing the turbo to work as hard to maintain pressure. Without tuning the wastegate duty cycle for a lower boost pressure at the trouble RPMs, this flutter can affect drivability and air/fuel ratios. 

For some more information, take a look at the following article by enginebasics: http://www.enginebasics.com/Advanced%20Engine%20Tuning/Turbo%20Surge.html


I'm afraid of stuff getting sucked into my BOV, what should I do?


First of all, BOVs/DVs do not suck in air, they are always blowing out air, as long as the engine is running. 

* There is a very small fraction of time, and by very small I mean infinitesimally so, where the BOV might suck in air between boosting and droping into vacuum.  If you are concerned about this you can put a high flow filter element on the discharge side of the BOV to give you piece of mind, but it is really not necessary. This does not apply to radial valves R35 and R55

Page 1 of 3 - Previous 1 2 3 Next All Page: Items per page:
Hide ALL Answers  |   TOP   |  Back   |  Atom Feed

Company, Business and Organisation names used in these FAQs may be trademarks of their respective owners.

Please Wait!

Please wait... it will take a second!