While my Evo was on the dyno at English Racing, a question came up as to whether my Synapse diverter valve was working correctly during throttle lift after WOT. I wondered a bit how I could verify whether it was working correctly, when I realized that I can just hook one of my spare pressure sensors up to my UICP to log pressure in the UICP. So far, I've tested my stock DV in the stock push configuration and my Synapse in two push arrangements and one pull arrangement. Results are below. UICP pressure is the green line with the black Xs.

I knew the stock DV wouldn't hold my boost level (33 psi peak), but I needed a baseline comparison for UICP pressure at throttle lift. As can be seen in the first plot, it held about 30 psi, but as far as UICP pressure goes, at throttle lift, pressure spikes up an impressive 10 psi, and it takes roughly 0.6 seconds for the UICP pressure to fall below 5 psi.

The next three plots are for the Synapse DV. For those not familiar with the Synapse DV, it has two vacuum/boost ports. Port A has a smaller surface area than Port B. One or both ports can be used to provide different levels of closure or opening force on the valve. I'm currently running the Aby@mil.spec spring which is somewhat softer than the spring that comes with the Synapse DV. I do have three turns of preload, but it is still softer than the Synapse spring with no preload.

The first Synapse plot shown is with the DV in push format with Port B connected. Push mode should produce the most rapid pressure relief because both the vacuum pressure in the manifold and the boost pressure in the UICP are pushing to open the valve at throttle lift (just like the stock DV config). The Synapse has pretty much the same pressure relief characteristics as the stock DV. The main difference is that it doesn't leak and holds 33 psi.

Next, I tried the Synapse in push mode with Port A and Port B connected. This produces both a stronger closure force and a stronger opening force than with just Port B, although according to the Synaptic rep, using just Port B is most effective at relieving UICP pressure. Turns out that the result is pretty much the same as using just Port B.

Lastly, I put the DV into pull mode with Port B connected. Pull mode is potentially tough on turbos because opening of the valve at throttle lift relies only on the manifold vacuum, so it is usually assumed that this config does not relieve pressure as effectively. And in the case of the Synapse, the UICP pressure actually acts to hold the valve shut during boost. Anyhow, as the plot shows, it has the same pressure relief characteristics as the two push configurations which I find quite surprising. I thought that for sure there would be more of a delay in pull mode. A mildly surprising result is that the Synapse in any of the three configs that I tried is no faster than the stock DV at relieving pressure. It is touted as being ultrafast acting, so I was expecting it to relieve pressure noticably faster. Ultimately though, its as effective as stock at relieving the pressure, and it can hold boost, so it is a step up over stock.


Stock DV in stock (push) configuration



Synapse DV in push mode with Port B connected



Synapse DV in push mode with Port A and B connected



Synapse DV in pull mode with Port B connected

 

Thanks for doing this test! It's nice to finally have proof to back up this DV. I'm glad to see that push and pull mode are relatively the same as I had to change my configuration due to the perrin intake I just installed. I'm also running the exact same configuration as the last graph so I now know exactly what's going on. Much appreciated

 

So, thinking about this a little more, perhaps the spike is unavoidable because the turbo is pushing ~500 whp worth of air at the moment of throttle lift, and the 1.25" diameter tubing flow path for the DV may not be large enough to effectively relieve 500 whp worth of air instantly.

 

Thanks for the testing.

I would like to see this test with a Tial BOV running the softest spring set to open by 8-10in of vac.

All stock EVO BOV start leaking right around 27psi.

 

Thanks for posting results of another interesting test. Safe to assume that you'll be going with "Synapse DV in push mode with Port A and B connected" moving forward?!

 

Good testing Mrfred, I feel that the synapse products really work well with the evo's uber sensitive system... I have had the larger style BOV for a few years now and no issues to report... I still have port C on that big boy...

 

If you have one available, let's throw it on my Evo next time I'm by the shop (hopefully in a week or two). Since you mention having the TiAl open at 8-10 in of vacuume, I'll mention when I had the Synapse hooked up to Port B, there was just enough vacuum for the valve to gently slide open at idle. (I had the exhaust side of the Synapse removed from the intake pipe so I could watch the valve as I tried different port combinations.)

Not sure what I'm going to settle on. Apparently, any setting gets me the same pressure relief performance. Best I can say right now is that for driveability, I think I like pull a little better.

 

motoiq did this a while back too

http://www.motoiq.com/magazine_artic...ter-valve.aspx

 

Interesting. Based on your charts below, push with A & B connected appears to provide the most consistent AND minimal pressure differential between your boost and UICP pressure readings under acceleration, which appears to help with knock, even if marginally. By driveability, I'm assuming you're referencing partial throttle and partial boost? If so, what are the differences that you've noticed?

 

Interesting article. I has more data. :-)

I think any of the configs will hold the same boost. The variations in the plots I think are due more to ambient air temperature differences. I'll probably default back to pull with port B only. It had good drivability.

 

I drove around town today in push mode with port B connected, and I found that I was getting a fair bit of clutch stutter when pulling away from a stop. I'm pretty sure its due to the DV fluttering open and shut because I don't get it in pull mode, at least not as badly as I did today. Going to switch back to pull mode to see if it goes away as I expect.

 

Ive tried a few configs and pull with port B def worked best for me too

 

Great test mrfred, thanks for doing it! I wonder how the test results would differ with the OEM spring from Synapse compared to Aby's spring with preload...

 

I expect there would be no difference in pressure holding capability and likely little or no difference in pressure release response. The spring constants are not radically different.

 

hey freddie when you say you have the larger style BOV which one do you mean ? i bought one oh about a year ago from STM for my 2G, still in the box n the serial number on the package says 16001A. Is this the same one you have ?