965 BOV Conversion - regrets?

[donbecker1234]

I'm currently refreshing my '79 930 CA motor with new fuel, oil and vac lines as well as easy to get to seals and sensors. I'm replacing a leaking fuel hose, and all the other fuel and oil hoses to be safe and the vac lines to preemptively prevent any vac leaks since everything looks original. Aside from an initial warm up issue on my car, it seems to run fine for the time being.

The factory Bypass Valve / Turbo Valve Housing looks simple enough to replace the gaskets on, but I've read quite a few threads on deleting the Turbo Valve Housing and converting to the 965 Blow off valve.

For those that have done the conversion, what are your overall thoughts on it?

How much have you driven your car since the conversion, and are you overall happy with it?

My home garage is pretty well equipped to fab up anything needed, as I have a variety of metal fab equipment and can weld aluminum.

It seems there are two camps on this mod:
1. Do it, take all this stuff off the engine, it's great, everything is fine and/or better with it gone
2. It worked for me but I'm aware there are risks to the turbo so bad things might happen to you / your car.

I'm wondering just how frequently people who have done this mod to their cars are driving them, and although I haven't read any threads where people reported negative consequences related to it, it seems like a whole lot of effort on Porsche's end to have engineered and put all this stuff on the engine.

Is the 965 BOV conversion truly equivalent in operation to what came on the car stock?

Converting to the 965 BOV is probably going to be a similar effort and cost for me as refurbing the existing system so I'm on the fence.

I'm not too concerned about "looking stock" although I'm not a fan of the big red Fabspeed elbow.

I'm not chasing any increase in power on the engine here at the moment, I just want to drive the car.

[jwasbury]

you bought a car then...

my 2 cents: don't bother with 965 BOV unless you're already doing other things. Most of us ended up ditching the original 930 bypass valve housing because we changed to a "long neck" style intercooler. I'd refresh seals/gaskets and run it as is.

[donbecker1234]

Originally Posted by jwasbury

you bought a car then...

my 2 cents: don't bother with 965 BOV unless you're already doing other things. Most of us ended up ditching the original 930 bypass valve housing because we changed to a "long neck" style intercooler. I'd refresh seals/gaskets and run it as is.

Thanks.

The long necks look nice, just not in the budget at the moment.

[Mocker]

You'll need to either modify the stock IC or buy a long neck IC to do this anyway.

There is no downside to this mod, other than the cost of parts and mods. That's why Porsche did it with the 964 Turbo. The clunky bypass mechanism is much more troublesome and less effective than an elbow with a BOV.

[mark houghton]

This might interest you, and maybe not...but my unconventional method from years ago.

http://forums.pelicanparts.com/911-930-turbo-super-charging-forum/518667-bov-update-short-neck-ic.html

Not quite the elegant 965 BOV conversion that a professional might do, but it worked just fine. Beware that the housing material is magnesium, not aluminum, so you would need to know mag. welding to do this up right. I used JB Weld where needed and it held up just fine for this application and ran it for several thousand miles with no issues.

The benefit? Some minor weight reduction, shorter air path/less volume to fill with compressed air by getting rid of that recirc. manifold = maybe a quicker boost response, cleans up the engine bay somewhat. Was a fun project regardless of any benefits.

[spuggy]

Originally Posted by donbecker1234

Is the 965 BOV conversion truly equivalent in operation to what came on the car stock?

No, it's just better; you lose that entire casting and all the moving bits/seals inside it, and replace with a rubber/silicone elbow and something that weighs an ounce or so - and apparently reacts faster too (I posted a link years ago to some guy who tested the various SEAT, VW and Audio Bosch valves).

The sealed plastic Bosch valve weighs nothing. If it wears out, punctures the diaphragm or doesn't seal, throw it away and replace in about 3 minutes; no stripping the intake and rebuilding.

Billet replacements are only a little more - and are strippable, tunable (different springs) and rebuildable (although I'd unscrew the cap to look inside mine every year to make sure it was still clean/had some grease and it was always perfectly clean/fine and showed little/no wear after 30K miles).

That said, Jacob hits the nail on the head - something to do when you go long-neck for a better intercooler.

[donbecker1234]

Originally Posted by spuggy

No, it's just better; you lose that entire casting and all the moving bits/seals inside it, and replace with a rubber/silicone elbow and something that weighs an ounce or so - and apparently reacts faster too (I posted a link years ago to some guy who tested the various SEAT, VW and Audio Bosch valves).

The sealed plastic Bosch valve weighs nothing. If it wears out, punctures the diaphragm or doesn't seal, throw it away and replace in about 3 minutes; no stripping the intake and rebuilding.

Billet replacements are only a little more - and are strippable, tunable (different springs) and rebuildable (although I'd unscrew the cap to look inside mine every year to make sure it was still clean/had some grease and it was always perfectly clean/fine and showed little/no wear after 30K miles).

That said, Jacob hits the nail on the head - something to do when you go long-neck for a better intercooler.

In the stock setup, the intake is tied to the BPV right? How does that work in the converted setup?

What impact does losing that connection have on the way the engine works?

Sorry if this is an obvious answer, I'm new to these cars.

[spuggy]

Originally Posted by donbecker1234

In the stock setup, the intake is tied to the BPV right? How does that work in the converted setup?

I'm gonna assume you mean "by-pass valve" from context.

Going from memory (years since I had CIS), the 965 elbow is connected between the air flow meter (right guys?) and the turbo intake. The Bosch valve sits in it, and is connected to the intercooler - eg intake, pre-throttle plate/post-turbo. And there's a vacuum line run (from under the throttle plate) to the top of the recirculation valve, which actuates it.

When you lift off the throttle, the turbo doesn't come to a dead stop, because physics (you'd be sorry if it did) - it's still spinning at insanely high RPM. So there's excess airflow/pressure on top of the throttle plate, going nowhere because the the throttle is shut. But you have vacuum under the throttle plate - which is used to open the recirc valve and divert the air back into the intake, pre-turbo, so it goes around again.

If you don't do anything with this air, you get compressor surge - airflow stops/pressure peaks and the turbine blades stall. Air actually comes backwards out of the turbo. Distinctive sound, not good for turbo longevity.

With CIS, it's supposed to be important to retain the metered air, so as not to mess up the fuel ratio (as that is based on the air that went past the air flow meter). Some have said it's not critical, as the duration the mixture is messed up is too short - but that's how the factory designed the system.

With EFI cars running a MAP sensor, you don't track metered air. So you can do whatever you like with it; return it into the intake - or dump excess into atmo in favor of fresh/cool air that hasn't been pre-heated by going through the turbo already.

Personally, not a huge fan of the sound of atmo dump valves; but if you have the heater vents open, you'll get enough of that expelled air picked up by the engine fan and come through into the cabin to know that it's pretty hot/oily. Also a pretty good tell-tale for how fast you're building (or leaking) boost when shifting in the lower gears.


This has a fairly good explanation of compressor surge and BOVs:

https://themotorhood.com/themotorhood/2016/3/14/p6rwfjc50rjfsr2vtqkk3njyfv84bn

There's many examples of compressor surge or "turbo flutter" on YouTube as well.

Originally Posted by donbecker1234

What impact does losing that connection have on the way the engine works?

You don't lose that connection. The entire magnesium assembly is replaced by a tiny plastic valve that fits into the rubber (or silicone) elbow. It does exactly the same thing, for the same reasons.

[donbecker1234]

Thanks for explaining that! So the BOV in the 964 setup vents to open air, and the stock 930 setup routes that same air back into the intake?

[spuggy]

Originally Posted by donbecker1234

Thanks for explaining that! So the BOV in the 964 setup vents to open air, and the stock 930 setup routes that same air back into the intake?

No. Both the 965 and the 930 are CIS, and both recirculate excess boost.



3 ports on a Bosch-style recirc valve, 2 large (25mm) ports and a vacuum control port on the top. The one out the bottom is the outlet (and goes into the 965 elbow), the one that sticks out the side goes to the intercooler on a 930 (or somewhere between the compressor outlet and the throttle plate).

[krasuskyp]

agreed w/ what's been said

will add that yes 965 valve remedies at least 'some' of stocker throttle lethargy - and those improvements only get better as you do other things

slippery slope heh heh

I was in same budget, sold my stocker i/c for a used Garretson found here (then that for a full bay long neck Bell heh heh) - point is... there's ways to do it net cost neutral

again... slope beware

[donbecker1234]

Originally Posted by krasuskyp

again... slope beware

Yep, I've been considering the slope in what I've been doing to my car. Mods to come later after a good baseline.

Replacing seals and other bits on the original system hasn't been too much money all in all.

[gorskined]

Originally Posted by spuggy

No. Both the 965 and the 930 are CIS, and both recirculate excess boost.



3 ports on a Bosch-style recirc valve, 2 large (25mm) ports and a vacuum control port on the top. The one out the bottom is the outlet (and goes into the 965 elbow), the one that sticks out the side goes to the intercooler on a 930 (or somewhere between the compressor outlet and the throttle plate).

what is the prefered take off for the vacuum control port can i simply branch off the distributor line?