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 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. ? 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 ( compressor surge?), or even know how to identify it ( 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: