Decel valve delete and idle

[mooney265]

Originally Posted by 911nut

A mechanic friend told me that this could be remedied by collapsing the vacuum side of the "can" 1-2 mm. It worked and I now have mine hooked up to the intake once again.

I think JF Fairman suggested that, too. About 1.5yrs ago on this forum...

I may put mine back on and do that, too. I removed mine because the rpm's were hanging for too long - - felt like I was going to run into the back of the car in front of me after I lifted...

[oilonly]

Newb question, how does one collapse the vacum side?

[JFairman]

I've never done that to a deceleration valve but I've done it to stock bosch EFI fuel pressure regulators on BMW's in the past. You're compressing the spring inside and raising it's preload against the internal vacuum diaphram.

With the bosch FPR you put it in a bench vise with a correct size 3/8 or 1/2 drive socket on each side and squeeze it a little at a time to compresss the vacuum line end side of the steel canister inwards concave a little to compress the spring on the inside to raise the preload tension on the vacuum diaphram a little at a time until you get it where you want it.

Same procedure might work on a deceleration valve with correct sized sockets or whatever.

[911nut]

Originally Posted by mooney265

I think JF Fairman suggested that, too. About 1.5yrs ago on this forum...

So Mooney, are you saying that I don't get any brownie points for my response?
I hate it when that happens

[mooney265]

Originally Posted by 911nut

So Mooney, are you saying that I don't get any brownie points for my response?
I hate it when that happens

he suggested it [i didn't say he 'did' it...] i'll find it...

And, yes you do deserve credit for reminding me of the fix...

[IMONBOOST]

Had it removed on mine, no real difference for me at least.

[mark houghton]

When I took mine out of the equation (well, it's still there but instead of recirculating the boosted air, it just vents it) what I have found is that the rpms drop instantly when shifting vs. hanging up there...which is why I did the mod if the first place. Yes, it will draw air into the mainfold in an overrun condition (off the throttle, vacuum opens the valve). No problem, I simply installed a small air filter on the end. Now, when fully off the throttle, I see my AFR's leaning out as would be expected.
Will this mod make your 930 a ricer and gain all sorts of performance? Not....Just vents a little more boost pressure between shifts and minimizes the 930 "cackle" when decellerating off throttle. That's been my experience anyway.

[j930]

I have been having a hanging RPM and was looking for a solution. I spoke with the head guy at the Dealership i have been working with and he said that Porsche back in the day had the guys compress the valve 1 mm to fix the hanging RPM problem. its funny that i stumbled upon this thread as i had been searching for a while for the solution. this is a great knowledge center!

[Kraftday]

Interesting read on the experiments and the zeitgeist of the BOV / diaphragm regulators. I've had the notion the diaphragm regulators acts as a damper so removing generally causes crisper on / off throttle response. But when removed for whatever reasoning, different, non original configurations are there to factor..

Some other factors worth mentioning are effects of the mass of the flywheel / clutch assembly, intermediate volumes and catalyst / muffler systems, etc. I view it as a drivability and safely component of the emissions control, as a system.

Having machined and sold thousands of billet repro boost control valves over the past 12 years, I've had some time to question designs and argue with the correct way to use these.. Now, I generally believe following the engineering examples set by the constructors. So what did Porsche / Bosch do on the 965-or motorsports? Bosch really designed an engineering marvel with the original 930 system..but with emissions constraints. Now later or Motorsport / Bosch commits to recirculation type valve design ("Over-run cut-off valves"). Some reasons being emissions which not many care about or noise levels or not wasting metered air. The most important reason is reducing boost surge, thus protecting the turbocharger! Now if you wanted to stick with venting to atmosphere this will be louder but also because they are metal where as Bosch re-circulating type valves are a polyamide and thus quieter.

Some time ago (around 1999), ZucZ Performance had a “Long Neck” conversion package which consisted of a billet 3D machined adapter and updated to the 965 cut off valve. It was a slick, expensive package with some ugly machine work on the adapter but they worked (with the diaphragm regulator needed) and were sold to Performance Products / Automotion at the time. Unfortunately, not much empirical testing or feedback was there with just that part only replaced.. so never knew if it was worth it.

[1SIK930]

Mark,
Now that you've had your decel valve vented to atmosphere for some time now, what do you think? I'm considering doing the same thing to my 930. Mine's a little different because I have an Andial IC. I still have my whole re-circulation valve.
Did you cap off the intake manifold?
Are you getting more or less exhaust popping?
Do you ever have a problem coming to a stop and the engine dying?(something I heard about from doing this)

[mark houghton]

Originally Posted by 1SIK930

Mark,
Now that you've had your decel valve vented to atmosphere for some time now, what do you think?
Did you cap off the intake manifold? Yep. See the attached picture of the mouse-nest as I did my recircvalve delete thing. Look at the inner bend of the turbo air intake hose elbow and you'll see the original large vacuum hose capped and tapped with a smaller vacuum hose which I am using to actuate the BOV (in this pict I hadn't yet installed the decel valve)

Are you getting more or less exhaust popping? I never really had any popping prior to the delete, and now I might get a pop or two once in awhile. So I guess maybe just a little more popping but not at all obnoxious.

Do you ever have a problem coming to a stop and the engine dying?(something I heard about from doing this) No issues there. I would think a simple mixture adjustment would remedie that.

I run a small air filter attached to the free end of the decel valve, just as insurance against drawing in any unfiltered air.

[myturbo2]

I have to replace the gaskets in my DV and have been following these related threads. This may be a dumb question but, it sounds like it would be easier just to go to a long neck intercooler and do away with this problematic area all together. Am I wrong or am I heading down an expensive road?

[mark houghton]

Originally Posted by myturbo2

I have to replace the gaskets in my DV and have been following these related threads. This may be a dumb question but, it sounds like it would be easier just to go to a long neck intercooler and do away with this problematic area all together. Am I wrong or am I heading down an expensive road?

There aren't any gaskets associated with the DV (deceleration valve). You're probably referring to the boost recirculation valve housing, where worn gaskets cause a clunky sound when getting on/off the throttle.

If you still are running with the stock IC and plan on going with something larger, then yes....a long neck IC will allow you to delete the boost recirculation assembly all together..with a few minor add-ons to complete the project.

[oilonly]

Originally Posted by myturbo2

I have to replace the gaskets in my DV and have been following these related threads. This may be a dumb question but, it sounds like it would be easier just to go to a long neck intercooler and do away with this problematic area all together. Am I wrong or am I heading down an expensive road?

Like mark said you might be talking about the whole BOV assembly that the decel valve is connected to. The decel valve is the Gold colored disk that I retained when swithching to a long neck to get rid of the whole BOV manifold.

Video here.
930 engine.3gp - YouTube

[myturbo2]

You guys were right, I was thinking of the BOV. Still a great thread and I'm enjoying reading it.


Oilonly... went to your video and where did you get the air cleaner?

[oilonly]

Oilonly... went to your video and where did you get the air cleaner?

I bought it from a poster on this site, JFairman. Don't know the name brand.

[1SIK930]

Mark,
Thanks for your input back. I can't wait to hear what it sounds like. The car's that I've had before this 930 were a few fixed up turbo charged Mitsubishi's including an Evo IX, that all had BOV's that vented to atmosphere. Not to mention, I just went to Rennsport Reunion IV, where I got to here the BOV's of the 962's. What an awesome sound. I'm sure it won't be that loud but...