For those of you who have built, designed, or install HKS BOV (either one) for Porsche Turbos, please input.

**********
QUESTION:
1) Is the originating port for the vacuum signal tapped directly off the intake manifold?

2) There's an electronic controller that intercepts the vacuum signal between the intake manifold and BOV... what does it do?

3) If Io bypass this elec controller, would it throw CEL?

SPE? Akkurat? Anyone?
**********

ISSUE:
Here's the estimated condition under which the "problem" occurs...

- Light Throttle (15~25%)
- Light Boost (.1~.2 BAR)
- Light load (gentle acceleration)
- 2700~3500 RPM
- Usually 2nd or 3rd gear
- Mainly City Driving

When moving through those conditions, the BOV would occassionally open briefly despite the fact that system is under boost. It's not difficult to duplicate. I know it opens because I can clearly hear it. It's brief, but distinct. I've set the adjustable pre-load of the BOV to full finger-tight.

Now, from a performance perspective, I suppose it's no big deal, because when I do want to GO, the BOV holds boost just fine. WOT shifts yield chrisp turbo response. This only happens in a narrow window when performance is not required, but nevertheless, it should not be happening at all.

Thoughts? Anyone else experience this? Anyone... anyone... Bueller?

 

hmmm, try some japanese forums like supraforums.com or rx7club.com as they would have more experience with the hks ssbov, although it could just be your vacuum source.

 

The port is taken from the manifold, however it does run through a series of valves. Under boost the system is not under boost because of the valves. Only when you throttle off.

If you bypassed it it WILL throw a secondary air injection code air. That runs off of the same lines.

 

Steve, haven't used SSQ since 97-98'so unfamilliar w/the elec.tap-in but HKS says on their site that the small primary valve is DESIGNED to initially open under light load/throttle conditions and then under heavy load/boost opens the secondary larger valve. Also, they show the upper chambers of the valve divided by a diaphram "A" being the spring chamber and "b" the chamber fed by the vacume/pressure fitting. The lower chamber "b" is fed by i assume boost pressure or spike to counteract the spring and open the primary and then secondary valves. I would think that the vac line should be routed to a fitting on the "y" pipe before the throttle body-where does HKS reccomend? If there, the valve would open under boost spike/throttle closed.Still, i'm curious why they would design it to open at all on light boost or load. Maybe it in some way improves throttle response? Don't see how. BTW, does the car seem to lag at low boost ranges or is it simply the noise that concerns? Seth.

 

Stephen: Sorry I can't help bur just want to say "Way to go" for blazing a trail.

 

Thanks for everyone's input...

Node: I've actually got a lot of experience with HKS SSBOV and Type II valves (and just about any BOV), as I've run them in many of my previous turbocharged cars, including a T04R Supra. This is simply the first experience for me specific to our Porsche Turbos.

Porsche Tech: I think the issue (if it in fact is one) lies w/in the elec check/controller valves. Also, the signal port has to be after the TB, at the intake manifold. Otherwise, the BOV would never see negative pressure, causing the BOV to never open.

Stephen (IA): Thanks for the headsup on the CEL. If I understand you correctly, the check valve prevents positive pressure to reach the SSBOV signal port, and only allows vacuum to reach it. That could help explain what I am experiencing because the extra boost that the signal port should experience would normally help keep the valve shut under light loads.

Now that I know what the check valves do, I think I can bypass its functionality w/o throwing a CEL by capping off the output of that check valve altogether, and simply T the BOV signal line from right before the check valve. That way, the check valve sees everything normal, and the BOV sees what it needs to see... true manifold pressure, both boost and vacuum.

Also, based on yet another conversation with a trusted source, Porsche have have simply designed it this way, intending that the elec check valves do what they do. If this is true, while it is not a big deal with a recirculated system, when venting to atm with my SSBOV setup, I would still prefer the BOV to stay closed for obvious reasons.

Well, whenever I feel like get'n my hands dirty again, I'll dive back in and update everyone (and Tim!) with my findings.

 

BTW, please don't let this discourage anyone from going the BOV route, whether it'd be SP Engineering, Akkurat, or your own. I'm very happy with my setup thus far in terms of turbo response. And in fact, everything performs great. I'm simply trying to fine-tune and nit-pick that very last little bit to exactly how I want it to be, that's all... some would call it pursuit of perfection, others call it OCD!

 

Generally speaking does the e-throttle valve cause exhaust vs intake airflow matching issues different from a non e-throttle turbo motor?
Under light acceleration (with boost showing on the gauge) I assume the boost is blowing against the mostly closed throttle valve. Isn't the manifold pressure downstream of the throttle butterfly actually a vacuum under these conditions. I'm assuming the pressure shown on the boost guage is read upstream of the throttle valve. Even though the dash guage shows boost, the pressure at the intake valve is below atmospheric(?)
Under these (unneeded boost) conditions wouldn't you want the BOV/bypass open? The open bypass would let the turbo speed up relieving exhaust backpressure.(??) OR does the unneeded boost improve throttle response when you floor it.

 

Stephen...great write up. Definitely keep me posted with your setup. I didnt have as positive results, so the only conclusion based on your results must be that I had a defective BOV? It's going back today so the guys can retest the unit and see what's going on.

 

You bring up a very good point. I'm not sure which is more desirable... to have the bov open during that momentary transition where the pre-TB is starting to pressurize while the intake manifold is just transitioning from vacuum to positive pressure to aid in the spool up of turbo... or to simply have the BOV shut so that whatever excess pressure can be forced through the slightly open TB. I would tend to think the latter, but it's just my opinion.

In the end, I suspect it may simply come down to a philosophical difference, as I can see the arguement for both. And without spending time on the dyno with a few strategically located boost gauges and dyno plots, we would not know definitively. It would be interesting to see what the Porsche engineers had originally intended for our cars' turbo system. I do find it odd that the boost sender is tapped off the ic pipes as opposed to the intake manifold.

I had a conversation with Sol @ Perfect Power over this very topic yesterday. It would have saved Porsche both money and R&D had they simply tapped into the intake manifold for the BOV signal. So, the very fact that they went the extra lengths to design and impliment a controller to intercept the signal makes me wonder what their desired goal was. Then again, it may come down to something as specific as the design of the oem Bosch valves.

On the Japanese turbo systems that I have worked on, they all tapped directly into the intake manifold. This is the first instance I've seen where a controller cuts off the positive manifold signal, thus only allowing the vacuum to get through to the signal port of the BOV. I recall check valves for some wastegate designs, but not BOVs.

I'll have to give this some more thought... any additional inputs welcomed.

 

Hey Bill,

I was actually thinking about your problem the other day... very strange. Could the orange o-ring have been accidently left out, causing the BOV to not properly seat against the flange?

When you were going back and forth between the Bosch and Type II valve to test the setup, did you leave the Type II in the y-pipe while running the Bosch? If you did, then this would NOT indicate a leak at the Type II and flange. Those Type II valves seal very well at the pull-valve. The only other places where the BOV would be leaking is either where the valve mates to the valve seat, or through the hole where the shaft of the valve goes to the signal side of the BOV. Hopefully, Akkurat can find out what the problem is. Keep us posted...

 

Actually alex had asked me the same thing about the oring....I totally forgot to check (as it could have been left out) until I just read this post. Can you visibly see the oring?

I did leave the typeII in the Ypipe when I was going back and forth between the typeII and DVs. I did mention before that it could have been the spring bolt as I was unable to turn it at all with my fingers. I tried to loosen it a tad with a socket and with VERY little effort, the bolt broke off. So, it could have not been threaded through correctly, thus the low boost readings? Im going to reopen the box and look for the oring. Thanks.