Pelican Parts
Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   Pelican Parts Forums > 1- Porsche Technical Forums > 911 / 930 Turbo & Super Charging Forum


Reply
 
LinkBack Thread Tools Rate Thread
Author
Thread Post New Thread    Reply
Turbo Hooligan
 
Join Date: Sep 2007
Location: Greensboro NC
Posts: 1,246
Quote:
Originally Posted by mark houghton View Post
People will tell you that the back-boost on your turbo is not good for it and increases lag by drastically slowing the turbo down during shifts. That's why the stock setup was not designed to vent to atmosphere. That seems to be the general consensus anyway, or what we've collectively talked ourselves into believing.
Yeah, they tell me that, but my turbo has a complete no fault 1 year warranty, and if it goes after that, well, turbos are wear items. what they don't tell you though is that the extra fuel hitting the turbine blades and igniting helps keep the turbo spooled. not good for the turbos life but does keep it spooling. and my transient response time is almost non existent so theres almost no turbo lag. that and man I love the psshhhh sound between shifts.
__________________
www.d-zug.com
blog.d-zug.com

All these guys do is drive too fast, work on cars, chase ******* and drink.. really no fun at all...
Old 11-05-2009, 11:09 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #61 (permalink)
Metal Guru
 
911nut's Avatar
 
Join Date: May 2001
Location: Michigan
Posts: 2,511
Garage
Quote:
Originally Posted by Ag02M5 View Post
One member plugged the intake and dumped the air to atmosphere.
That is me.
Why did the factory rig the bov to do this? For emissions. When the butterfly snaps shut in an n/a or turbo car, a tiny amount of fuel isn't completely burned, which raises the hc content of the exhaust. On a n/a car a vacuum-activated dash pot with a linkage to the throttle bell crank resists the sudden closure of the butterfly, allowing the fuel to combine with air and burn completely. On our turbo cars, the high pressure air trapped between the compressor and the butterfly is dumped into the intake, accomplishing the same thing.
I switched my recirc valve to a Forge bov after I noticed that my revs were dropping very slowly. Having to wait 3 seconds for the revs to drop isn't much fun. What I noticed after making the change was that, when shifting at 5000 rpm, I had an instant 2 psi with the bov vs. 0 psi with the diverter valve holding up my fun. My assumption is that taking a few tenths of a second to shift keeps the turbine from slowing down as much.
As for concerns about driveability, my car runs great; no issues. As far as unburnt mixture igniting in my turbo, well, I've seen that happen with cars that are running the recirc valve. The turbine wheel and housing are cast from nickel superalloy so it can stand up to raw fuel burning in it and a lot more. In checking my AFR's with an LM-1 I could not detect a rich spike when letting off the throttle to shift.
IMO making this change is a non-issue regarding durability and driveability and improves acceleration performance.
__________________
Paul B.
'91 964 Turbo
Port matched, SC cams, K27/K29 turbo, Roush Performance custom headers w/Tial MV-S dual wastegates, Rarlyl8 muffler, LWFW, GT2 clutch & PP, BL wur, factory RS shifter, RS mounts, FVD timing mod, Big Reds, - 210 lb
Old 11-05-2009, 01:24 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #62 (permalink)
Registered User
 
Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
With a CIS car we do not want to vent any air from the area after the air metering assembly.

Any air vented between shifts needs to be looped around the turbo to keep the AFR's in line.

If we do vent to atmosphere the fuel head will keep supplying fuel as if all the air being used by the motor. Thus, one will end up with a lot of fuel being dumped down the intake during de-accel.

I suspect some CIS turbo race cars may have done this as an anti-lag strategy as it can turn the turbos hot side into a little jet turbine as the fuel hits the red hot area. Not good for turbo life on a street-able car.

I am rusty on this thread but an instant 2 psi sounds with a 5k shift sounds very low to me.

On my C2 Turbo my boost gage stayed pegged between sport shift. I also pulled instant .2 bar off idle and instant .5 bar off cruse.

I believe the stock 930 dump system can work well if in good working condition. I believe many are in need of service.

I have seen evidence in some of the tuner articles over the years that a couple of the well known old school tuners have actually modified them to stay open at idle and cruse only close on acceleration like I did my C2T style BOV. This allows the turbo to spin up at idle or on curse creating a reserve so to speak. Then the valve would only close with acceleration allowing for much faster boost onset. If I had a 930 that was still using the stock BOV, I would figure out how to do this. (I would also convert my WUR to vac-sensing to get the metering plate moving quicker.)

I like having a throtle bypass valve (de-accel valve). It provides some surge protection like the BOV dose. If the BOV fails it be the only thing to save one from blowing off a hose or O ring in the area after the turbo or worse yet, snaping a turbo shaft in half. Further, it helps keep the boost up between shifts. It should not restrain a motor from coming back to idle quickly.

Last edited by 911st; 11-05-2009 at 01:53 PM..
Old 11-05-2009, 01:51 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #63 (permalink)
Metal Guru
 
911nut's Avatar
 
Join Date: May 2001
Location: Michigan
Posts: 2,511
Garage
Quote:
Originally Posted by 911st View Post
With a CIS car we do not want to vent any air from the area after the air metering assembly.

Any air vented between shifts needs to be looped around the turbo to keep the AFR's in line.

If we do vent to atmosphere the fuel head will keep supplying fuel as if all the air being used by the motor. Thus, one will end up with a lot of fuel being dumped down the intake during de-accel.



I like having a throtle bypass valve (de-accel valve). It provides some surge protection like the BOV dose. If the BOV fails it be the only thing to save one from blowing off a hose or O ring in the area after the turbo or worse yet, snaping a turbo shaft in half. Further, it helps keep the boost up between shifts. It should not restrain a motor from coming back to idle quickly.
Keith, I reiterate: Data shows no evidence of an AFR problem with my car in the instant that the butterfly snaps shut. The air metering plate will return rather quickly to the closed position due to the hydraulic force acting upon it.
BOV failure will not result in an instantaneous failure of the turbo. The telltale sound of the compressor in surge should be warning enough, but one would have to be running much higher boost than we can safely run to do the damage that you speak of.
__________________
Paul B.
'91 964 Turbo
Port matched, SC cams, K27/K29 turbo, Roush Performance custom headers w/Tial MV-S dual wastegates, Rarlyl8 muffler, LWFW, GT2 clutch & PP, BL wur, factory RS shifter, RS mounts, FVD timing mod, Big Reds, - 210 lb
Old 11-05-2009, 02:14 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #64 (permalink)
Registered User
 
Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
Hi Paul.

A few have done as you and have been happy with it so if it works for you that is great.

That is more an accepted strategy on an EFI motor that can shut off the fuel on throttle lift even if the EFI senses air flow.

Still, if any air is being bleed from the area after the metering plate, the plate is more open than it should be and more fuel is being sent than should be.

We already have issue with CIS (Continuous Injection System) in that it keeps sending some fuel to the motor on throttle lift. This is sometimes evidenced by the popping that is often heard of fuel burning in the exhaust tract.

Bleeding off air just sends even more unnecessary fuel on throttle lift. Thus, would not recommend it to others.

I ran without a functioning original BOV. What I did notice was the lack of the "swoosh" noise. The black plastic Bosch BOV's are known to fail.

With a stock 930 or C2 turbo the chance of braking a shaft dose not seem significant. However, as we step up to modified turbos with larger wheels (larger levers-higher load), the risks increase.

It would make sense that the higher the boost level the higher the potential. Also probably the higher the RPM. A speed shift at 7300 at 1.1 bar is probably going to exert a lot more load than a .8 bar at 6300rpm.

We do not hear of sheared shafts very often anymore. However there was a recent report of blowing off a boost hose on one of the 930's here with a shift.

Go for it if it works for you. However, it is not that hard to do it right and there is not any draw back I can think of in the way Porsche dose.

Forgive me if we already covered this.

I am not an expert, just what I believe.

Last edited by 911st; 11-05-2009 at 03:04 PM..
Old 11-05-2009, 03:01 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #65 (permalink)
Registered User
 
mark houghton's Avatar
 
Join Date: Jul 2008
Location: Central Washington State
Posts: 3,741
boost sending unit relocation

So if you do the conversion and do away with the stock recirc assembly, where do you mount the boost gauge sending unit (that big ugly orange rubber covered thing)?
__________________
Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 11-05-2009, 05:56 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #66 (permalink)
Registered User
 
Join Date: Jul 2006
Location: S. Florida
Posts: 7,223
If you get a long neck intercooler made for your car it will come with a threaded boss for the boost gauge sender and everything else that was on the intermediate manifold.

If you cut up the origonal one to keep your short neck intercooler while going to a C2 hose and recirculation valve, you can cut a square section to weld on where you cut the rest off out of the oem valve housing that has the threads for the boost sender and weld it on.

I have a picture of one like that but it would take a while to find it.
You'd still have to weld a support arm onto the left rear that goes down to an intake manifold boss that is now available.

My boost sender doesn't have an orange rubber on it. It was replaced before I got the car.
Old 11-05-2009, 06:14 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #67 (permalink)
Registered User
 
mark houghton's Avatar
 
Join Date: Jul 2008
Location: Central Washington State
Posts: 3,741
Quote:
Originally Posted by JFairman View Post
If you get a long neck intercooler made for your car it will come with a threaded boss for the boost gauge sender and everything else that was on the intermediate manifold.

If you cut up the origonal one to keep your short neck intercooler while going to a C2 hose and recirculation valve, you can cut a square section to weld on where you cut the rest off out of the oem valve housing that has the threads for the boost sender and weld it on.

I have a picture of one like that but it would take a while to find it.
You'd still have to weld a support arm onto the left rear that goes down to an intake manifold boss that is now available.

My boost sender doesn't have an orange rubber on it. It was replaced before I got the car.
That's what I thought. I will be keeping my shortneck IC and cutting up the intermediate manifold. Will have to weld a plate across the opening where I cut the manifold, so figurued I would just weld on a bung on that flat surface...or something like that. If you come across any picts, much appreciated.
__________________
Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 11-06-2009, 06:15 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #68 (permalink)
Registered User
 
Join Date: Jul 2006
Location: S. Florida
Posts: 7,223
found the pics

Hey Mark,
Went looking through the zillions of pics I've saved and found another pic that'll possibly help me with my fuel pump relay ~auxillary~ wiring nightmare.

I didn't take these pics of the cut and resectioned intermediate manifold so hopefully no one minds..

It looks like they cut out a rectangular section of the manifold that has the boss or bung for the boost gauge sender and used that to weld over the cut off section.
Or they drilled and tapped the threads for the sender from a different piece.

It's cast magnesium.


Old 11-06-2009, 07:22 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #69 (permalink)
Registered User
 
Ken911's Avatar
 
Join Date: May 2005
Location: Loxahatchee, florida
Posts: 2,657
ok so where do you find someone who can weld magnesium?
__________________
88 turbo Guards red Targa slant nose, and yes I am a horsepower junkie, 3.4liter,7.5 to 1 JE pistons, Adjustable WUR, Imagine fuel head, 1 bar waste gate headers,allthe cis toys. Now apart to become the next EFI monster. fabbing my own intake, headers Individual throttle bodies, MS-3, pauter rods, Xtreme twin plugged heads, gt-2 evo cams cop's.
05 Cayenne S lapis blue
Old 11-19-2009, 05:17 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #70 (permalink)
Registered User
 
mark houghton's Avatar
 
Join Date: Jul 2008
Location: Central Washington State
Posts: 3,741
Quote:
Originally Posted by Ken911 View Post
ok so where do you find someone who can weld magnesium?
That my friend is a good question. I plan to have one of my maintenance dudes do the welding for me....he's a pro at aluminum, stainless, almost anything....so I guess I'll find out if he can do this as well. I expect my "spare" diverter assembly to arrive in the mail any day now, hook up to the chop saw and hack off the end, then go from there.
The really neat thing about magnesium, if you've ever played with it, is that once she gets to burning it's white hot bright to blind you. Amazing stuff.
Do we know for sure that these are made of magnesium, of maybe some alloy with aluminum? Might be helpful to the welder to ID just exactly what the makeup is,
__________________
Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.

Last edited by mark houghton; 11-19-2009 at 06:04 PM..
Old 11-19-2009, 05:59 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #71 (permalink)
Registered User
 
Join Date: Mar 2000
Location: Auburn,In. U.S.A.
Posts: 2,449
Mr. Mark,

Glad to hear your going to get off your butt and do this. You will really like the difference. Ya got to roll the old girl back out and try it with the change once before you tuck her away for winter. It will give you more to look forward to in the spring.

Cole
__________________
Cole - 80 930 "The Old Sled"
Mods: TurboKraft Custom IC, 934 Headers, GSX 61, Zork, Port Work, SC Cams, Air Mod Fuel Dist Relocated, Water Meth Injection, BL WUR, MSD 6530, Greddy EBC, Synapse Bov, Short 2nd & 3rd with 8:37 R&P, Wevo Shifter, Coupling, and Mounts, MTX-L SSI-4, Big Brakes, Rebel Coilovers, Bilstein Sports.

Last edited by cole930; 11-19-2009 at 06:43 PM..
Old 11-19-2009, 06:38 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #72 (permalink)
 
Registered User
 
Join Date: Jun 2009
Posts: 687
when you do this modification on a stock type intercooler .I iunderstand how the I/C holds on the right with the cut modified stock magnesium part but how does the I/C mount on the left since we lose the left part of the stock POV?
Thanks
Old 11-22-2009, 07:14 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #73 (permalink)
Drivin' Miss Daisy
 
benzyne's Avatar
 
Join Date: Aug 2006
Location: Vancouver, Canada
Posts: 272
Garage
Quote:
Originally Posted by nreed View Post
Those of you considering BOV's should look at the BOV from Synapse Engineering. From my experience, this type of valve works much better. Fits between the turbo and intercooler.

Synapse Engineering

Hard to see in this photo but it's below the intercooler to the left of the fan. Recirculates back into the filtered air plenum before the turbo.

Has anyone used a Synapse BOV in the stock position at the top left of the IC? I just saw one of these items in person the other day, and they look quite a bit bigger than the stock unit. I'm wondering if there are any issues cramming it into place. Pictures would be much appreciated. BTW, this is for a 92 964 Turbo.
__________________
58 VW Split Window Bus - Porsche Powered
78 911SC Turbo Look - Megasquirt II, EDIS, 964 intake
92 964 Turbo
Old 11-22-2009, 10:26 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #74 (permalink)
Registered User
 
mark houghton's Avatar
 
Join Date: Jul 2008
Location: Central Washington State
Posts: 3,741
Quote:
Originally Posted by ertech View Post
when you do this modification on a stock type intercooler .I iunderstand how the I/C holds on the right with the cut modified stock magnesium part but how does the I/C mount on the left since we lose the left part of the stock POV?
Thanks
When I get around to completing this mod this winter, I'll take a buch of pictures on what I end up with. I think it's just a matter of fabricating some aluminum or stainless mount(s) to attach to a handy engine stud somewhere.
__________________
Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, stock everything else. The result of a massive Pelicanite good will fire recovery effort. Truely an open book, ready for the slippery slopes to modification.
Old 11-23-2009, 08:10 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #75 (permalink)
Registered User
 
Join Date: Jul 2006
Location: S. Florida
Posts: 7,223
When you remove the big origonal blow off valve housing or intermediate manifold there will be 2 unused 8mm threaded bolt holes in the intake manifold that were used to hold the oem housing onto the intake manifold.

Then you will have to weld on an aluminum support bracket to the back of your short neck intercooler if you're using that.
The bracket goes down to the bolt hole or threaded boss that is closest to the CIS air flow meter housing.
It fits and works perfectly and it's alot easier to remove and reinstall than the origonal setup with it's harder to get at hoses and hose clamps.

Here's a pic of the back of the used long neck half bay garretson intercooler I have on my car before I cleaned it up, polished it a little and installed it.
You can see the support bracket on the back.

Left to right the fittings are:
cold start aux air valve, throttle body, deceleration valve, oem boost gauge sending unit, the rear mounting bracket, 2 small fittings are for the wastegate hose fitting (a 90 degree fuel line fitting will screw in there for the hose) and the overboost sending unit, and the larger one is for the hose going to the C2 blow off valve you'll be using in the big rubber hose origonally for a 964 turbo off the CIS unit with a long neck intercooler.

The other hose connection for the decel valve will be visable on the intake manifold after you remove the origonal blow off manifold, it will be right below where the decel valve fitting on this intercooler is when it's installed.
Using it as a throttle body bypass valve/vacuum limiter valve like it is origonally installed is optional and up to the user.

I plugged the intake manifold fitting and currently have the decel valve venting to atmosphere because I like the little fooosh sound it makes if you have .3bar or more turbo boost when you let off on the gas between upshifts and it richens the mixture to around 10:1 on deceleration which is not a problem.
If it is hooked up to vent back to the intake manifold like it origonally does it slows down engine deceleration between upshifts as if the flywheel gained another 30 pounds and I really don't like that..
It may actually improve throttle responce a little when you get back on the gas during upshifts because it helps keep the turbo spooled up along with the blow off valve with a closed throttle between shifts andventing metered air to atmosphere between shifts makes the fuel mixture just a little richer the instant you get back on the gas kind of like an acceleration pump would do in a carburator.

Here's a pic of the bottom of my intercooler while installed showing the decel valve vented to atmosphere with a small downward angled hose to keep water from getting in if caught in rain or a carwash.
Old 11-23-2009, 09:21 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #76 (permalink)
Registered User
 
Join Date: Oct 2007
Location: Idaho
Posts: 193
Quote:
Originally Posted by djdawson2 View Post
I kind of find myself wondering if there is any real data to support switching from the OE 930 arrangement to the 965 or external BPV setup.

Having had the stock unit apart, I can tell you that it is very large. I can also tell you from experience that the plastic Bosch units, Forge, etc... could never possibly flow the volume of the one in the IM.

So I have to ask... why does this seem like a good idea? Is there data to support any change in performance (no butt-dyno results please)?

Dave
I have the same question. If there is an advantage then I would like to do this at some point if it will lessen turbo lag. I am willing to accept butt dyno impressions also -just want to know if it is worth the effort.
Old 11-23-2009, 09:34 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #77 (permalink)
Registered User
 
Join Date: Jul 2006
Location: S. Florida
Posts: 7,223
I've wondered that too but if it wasn't an improvement the factory wouldn't have done it in the 964 turbo/965.

It doesn't make a huge difference on a stock car but turbo lag is reduced a little since there's less volume for the turbo to repressurize after an upshift and the air flow going to the throttle body is straighter.
The smaller blow off valves react faster and there are many to choose from and you can choose which way you want to mount it, upright or sideways.

And, it frees up so much room under the intercooler... you could even mount fan to the bottom of the intercooler to suck more air through it, and it allows the use of more aftermarket intercooler upgrades.
Old 11-23-2009, 09:53 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #78 (permalink)
Registered User
 
Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
One could look for a 91-94 take off manifold or use it as a model.
Old 11-23-2009, 02:23 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #79 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 05:37 PM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2018 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page
 

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.