All hoses, transitions, hose clamps are new and tight! Pressurized the intake at the IC inlet and sprayed soapy water all over everything. The only place that had a leak was at the IAC and the CV valve connections, which I have epoxied and checked out ok. The only thing I haven't changed is the KLR line. Funny if that KLR line was the problem!!! Turbo rebuilt and looks and feels excellent!

BTW is it really possible to achieve 18 psi with the K26/8 and a MBC?

Thanks
Mike G.

The KLR line can be wide open and it wont really effect boost, other then misreporting to the gauge in the car. Eventually the low boost error from KLR will happen.
Sox

Here is first draft of the 1986 951 turbo/engine power and air flow stuff.
Was done on napkin to start with will fix/refine as I go along. "that is car makes 220hp " not make.
I used 85 % for turbo efficiency...I also don't have the compressor charts for the turbo.
Sox

Sorry that data was wrong...will repost.
Sox

I have a compressor map for the K26 and it's in the 75% range at max required mass flow.

Thanks
Mike G.

how about the BOV, are you using the stock plastic one? i have heard of brand-new factory BOV's failing right out of the box because they have a flimsy rubber diaphragm seal. have you tried removing the BOV and blocking the holes to see if boost holds? or testing this BOV on another 951 to see if it holds boost?

i upgraded to the evolution billet BOV:
http://www.evoms.com/EVOMS_Porsche_Diverter_Valves_90_Deg_p/dv90degblk.htm

lindsey has some metal BOV's also:
https://www.lindseyracing.com/LR/Parts/944BOV.html

New factory BOV. The old one was shot but this new one made no difference. I did test it though with just lung pressure.

If I block the BOV isn't there a chance of a compressor blade problem when the throttle slams shut?

Dang man those BOV guys are expensive!

Thanks
Mike G.

BOV....bypass needs to be tested with a vacuum and enough pressure to mkae sure it does not leak boost.
So 10 to 15 psi on the side that goes to manifold, and it should hold. couple of inch of vac to allow it to bypass to the turbo inlet.
another subject you would not happen to have a k26/6 map ?
Sox

testing the BOV with lung pressure doesn't work, you can't generate 15psi with your lungs. :)

block the BOV to see if you get boost and ease off on the throttle so the pressure doesn't shock the compressor.

one of the reasons there's a market for the aluminum BOV's is because the stock plastic unit is so crappy.

sox: the k26/6 is so popular and old now that there's lots of compressor map photos online. just google for it. here's one:
https://gallery.rennlist.com/albums/albuq72/k26.jpg

Thanks Nize,
I think I might know a blowhard or two that could put out 15 plus psi with just their lungs :)
Sox

Ever seen Franco Columbu blow up a water bottle? haha

Its' at the end!
https://youtu.be/fx5TPoVMWV4

Thanks
Mike G.

Am in Dallas tonite...went to summit racing, talk about a kid in a candy store :)
Sox

Mike answer to your earlier question, thanks nize for the turbo map.
It works out to be 20.4psi @ 6500 rpm and top of the 75% efficiency, it is almost into 74 % but close enough.
So all things working correctly we should be able to do 20.4 psi . now the turbo heads towards 1.5 to 2.0 BP to boost at this point so the WG lets it leak way before that.
If your system is in good shape and you use a MBC (no protection) you can get the 20 psi.
Down side hotter turbo, more BP pushing the blades and way less MTTF, and gas being pushed back into the cylinders...
Sox

Nize
that map was for a k26-2670 GGa.
My 86 uses a k26-2667 GGA.

So mike above calculations for the boost are not correct...sorry :(

thanks Sox

Another matter, kind of still involved with WG/exhaust so will post here.
The installation of the wide band O2 sensor instructions state:

" On TURBO CHARGED vehicles:
Bung: Install the bung downstream from the turbo before the catalytic
converter. The high exhaust pressure before the turbo interferes with
the lambda measurement and the high exhaust temperatures
encountered there can damage the sensor."

In our cars the narrow band is installed before the turbo....so am I correct in just using the same spot or do I need to install a new bung ?
I have been using the existing bung for years and only had one sensor go bad, but are the readings being affected by the placement ?

Thanks Sox

Not really. We have some placed pre and post turbine and the readings are so close it's negligible. Anywhere between header and before CAT give the same reading. But sensor longevity is supposedly effected by more heat. Seems like you don't have an issue with that. Too bad I didn't know this before I welded an extra bung in, however it ended up in a position that makes it unusable. No Tequila was used for that bung positioning.

Thanks
Mike G.

"No Tequila was used for that bung positioning. "

Probably why it was not usable :)
Sox

Ok second cut at k26 /6 math...

http://forums.pelicanparts.com/uploa...1581960716.JPG

http://forums.pelicanparts.com/uploa...1581960741.jpg

Just use the Compressor flow at the rpm you are interested in and the boost level to figure out the efficiency point of the compressor.
As usual check my math/assumptions and correct as needed. Any interested in the math behind this I can post.
Sox

Well finally got all the sensors in and installed.
Went out for a quick run in the neighborhood, so only 2nd gear, more to test out the sensors then get max readings. Note the compressor outlet spike after throttle is closed but the BOV has not activated yet.
The forum image compression is causing the image to loose details...when I post more results will break it down into smaller images that the site won't try to compress.
Results below

http://forums.pelicanparts.com/uploa...1582572315.jpg

Cool stuff but I can't read the boxes!

Thanks
Mike G.

2nd attempt.

http://forums.pelicanparts.com/uploa...1582577465.jpg



http://forums.pelicanparts.com/uploa...1582577483.jpg

Run in 5th gear...ran out of runway early hence came off throttle at 3284 RPM.
Sox

http://forums.pelicanparts.com/uploa...1582582277.jpg

http://forums.pelicanparts.com/uploa...1582582277.jpg

Sensors and connections used to do the measurement.
Sox

http://forums.pelicanparts.com/uploa...1582583337.jpg

http://forums.pelicanparts.com/uploa...1582583337.jpg

having a hard time with uploads to the forum..

again...

http://forums.pelicanparts.com/uploa...1582583944.jpg

I know I am getting too far into the nitty gritty here but....
look at the pic. The boost (green) drops off multiple times while the output from the compressor (red) and the turbine back pressure ( orange) and RPM (black) stays consistent.
-Inter-cooler momentary block, not very probable.
-Throttle closing, but that would cause a spike in the compressor output pressure ( as seen in previous posts with gear change). Also its a direct cable connection to the gas paddle so I don't think so.
-Boost sensor in the KLR has noise/drop outs ?? don't know.
-Waste gate being told to open, but that would first be seen in turbine back pressure drop, which is not happening.
Any thing else y'all can think of ?
Thanks Sox

i'm guessing the cycle valve fluctuating is causing that and believe it's normal as it's doing its job.

Just out of curiosity what is the pressure drop here between these two circled points (imagine an image here, hahaha)?

Are you using different scales for each pressure measurement?

Do I need to have images hosted somewhere to be able to post them here? Can't I directly upload an image as a jpeg?


Thanks
Mike G.

Nize if it was the CV then the first thing to go down would be the Turbine inlet pressure, followed by the compressor outlet, and then the boost would drop.
As you can see the red compressor and the orange Turbine pressure are not dropping.
The CV opening would definitely cause them to droop first.
Sox

Mike don't follow your questions "red points" ???
You can upload jpegs here very easy..
In your posting pick go advanced, then upload image, it will give you 2 options drag and drop or browse to your image on your computer. either will work.
Sox

These two red circled points

http://forums.pelicanparts.com/uploa...1582729459.jpg

Thanks
Mike G.

Numbers in the boxes
Sox.

http://forums.pelicanparts.com/uploa...1582734283.jpg

i think your time frame is too small. every time the CV flips it can send a 'shock wave' of air to the KLR feed hose which can cause those minuscule (relative to time-frame) peaks and valleys. this is why quality gauges usually have a damper built in, otherwise the needle will be jumping around or vibrating.

it would also depend on where you're taking your reading, if you take a reading directly off the intake manifold from a dedicated feed and not a shared line it should be smoother.

This is something I always thought about when using MAP vs RPM to fuel/ign map an engine. There needs to be some filtering on the MAP or the control system would be unstable. Well I'm not a controls engineer but..........

Thanks
Mike G.

Boost reading is coming from the KLR. The compressor outlet is taken from banjo bolt on the hard pipe prior to the inter cooler. The turbine pressure is taken from the test bung on the cross pipe.
The KLR's electronics have built in smoothing function.....
Sox

Looking at the layout below I do not follow how anything the CV does can affect Boost at KLR without first affecting compressor out put. I do not see a link ??

Is the Boost pressure being physically measured with one of your sensors or is that the output from the KLR?

Mike G.

Out put from the KLR.
Sox