Unfortunately I have done all those checks and all hose are all brand new. Same boost level before turbo was rebuilt and after!

The only thing left is the exhaust so it comes off tonight.

Thanks
Mike G.

Well didn't have time to remove exhaust. But I'm going to use the port on the crossover pipe to see what the backpressure actually is. Then remove the exhaust if the exh press is more than 2:1 to boost press.

Thanks
Mike G.

Mike re-reading the whole thing again....
Since you have proven that with the WG held closed (vacuum) the car makes 2 + bars (14+ psi) your turbo is not likely to be the issue.
Let me get this right in my head:
Tube to WG pinched of you get 1.4 or so ?
WG held by applying vacuum you get 2+ bars ?
Looks like enough pressure is backing up in the turbo side of the WG to push it open because the air flow to you exhaust is limited IMHO. Sone where you have a partial blockage.
Sox

Yes to all questions and I want to check the back pressure but that damn port has stripped threads.

Mike G.

Well put a hokey BOSCH pressure gauge with a home made adapter (lug Nut) on the crossover and I get a shaky reading of about 20 psi. It reads pretty smoothly to 15 psi and then the needle jumps all over the place but will go past 20 psi which is the max on the gauge.

What should a K26/8 stock get for back pressure at a max boost of about 1.6 BAR?

BP/Int = 9psi/15psi



Thanks
Mike G.

Got my VDO 30 psi gauge, early for xmas hehe, and installed it. Guess what, 22 psi exh BP on the crossover pipe. For boost checking, using the stock gauge but I did check it before and it was ok.

So actually now I have BP/Boost = 22/9 = 2.4ish!!! DOH!!

Thanks
Mike G.

With Laust's car at 25-psi for over 2-decades now, we were seeing 45-50psi in crossover, sometimes 60+ if getting on WOT quickly at low-RPMs.

So your 22psi is high for K26/8, slightly high for K26/6 @ 9psi boost. Only getting 9psi boost may be sign that turbo's working too hard to generate this boost level.

At this point, we've narrowed down to some possibilities:

- clogged crossover, passing golf-ball through is rough estimate. If you can, borescrope entire length from header-flange to crossover for each cylinder. Then examine after merge to downpipe.

- worn-out turbo. Would need to get optical RPM-gauge and see how fast it's really spinning and where that ends up on compressor-map. I've seen many "rebuilt" turbos come back out-of-balance with pre-worn bearings. You can use dial-indicator to measure actual radial & axial runout. Also post picture with camera aimed directly into intake to see how much clearance there is at blade tips.

- intake-leak would also over-drive turbo with loss of boost. Clamp from J-pipe to inlet is common place for leaks. Also rips underneath J-pipe is common. Compressor-bypass valve can leak boost back to intake. I prefer sideways inlet so boost can't force valve open. I think Forge valve can be installed this way. It also has replaceable spring to allow stiffer spring. Although I think 993 unit works just fine. Conical hose going into throttle-body can slip off, examine it 360-degrees around where it clamps to TB. Do pressure-test with bubbles to find intake-leaks:
http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/769323-vacuum-leaks.html
http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/759766-afm-issue.html

- push/pull EBC for factory-wastegate. You can use 3-port metal boost-controller solenoid with one port attached to vacuum to increase wastegate-valve clamping like you did manually. This does appear to work to countreact crossover pressure and is used in high-boost applications such as Supra 2JZ-GTE engines with 45+psi boost.
- stiffer wastegate spring. I have procedure to increase spring-rate/preload of factory wastegate. Used in 25+psi applications. Laust also has mod to vent exhaust to pressure-side of diaphragm chamber that works well. But I think this just compensates for high crossover pressure in this situation.

https://drive.google.com/uc?export=d...PXCmVI2iDrVpAp
https://drive.google.com/uc?export=d...Ggjz2c6Njanb4y

Danno,
Just so that I am following you...

"With Laust's car at 25-psi for over 2-decades now, we were seeing 45-50psi in crossover, "

The 45-50 psi quoted was at the intake (exhaust) to the turbo from the engine ? Not from Turbo to WG ?

The pressure measured at the WG inlet (exhaust) on my car starts to push the WG valve/piston open at 22psi. With 0.2 inch shims it goes up to 25 Plus psi.
At that point I get about 11 to 12 psi boost.
Sox

How does a leak in the J-boot effect boost? I thought that the J-boot would always be under vacuum??? Also the J-Boot is brand new but I will check all the connections and do the bubble leak test there too. Compressor-bypass valve (BOV?) is also brand new and checked out ok.

The biggest air leaks I've found so far are the connector pins on the CV and on the IAC. Seems pretty lame to leak there!!!! I'm going to epoxy those areas and double check them with bubble spray.

Finally I really will remove the exhaust and check the entire damn thing.

Thanks
Mike G.

Took off CATPipe And tried to look down it with my crappy borescope on my iPhone. It was pretty tough to figure out anything from that. So I threw a ping-pong ball down the pipe and it stopped about 18 inches away from the flange. But to me it doesn’t seem like such a huge restriction especially when I look at the picture of the exterior of the pipe with the ping-pong ball laying next to it for reference.

http://forums.pelicanparts.com/uploa...1577723208.jpg



http://forums.pelicanparts.com/uploa...1577723939.jpg

what about the rest of the exhaust from the turbo to the tailpipe?
what about the exhaust manifolds from the head to the crossover?

Still working up to taking the crossover pipe off. I think that I’m just going to borescope the headers and hopefully be able to tell what the Hecks going on there. Do the headers ever collapse? I can see pretty good up the downpipe and it looks OK. I had it off about little over 1000 miles ago and it looked good too.

Mike G.

OMG I genuinely hate that crossover pipe! The ping pong ball rolls Through the pipe as freely as a dove in flight.

BOO!

http://forums.pelicanparts.com/uploa...1577915051.jpg

Used borescope with ping pong ball. Looks perfectly round all the way trough in crossover pipe.

http://forums.pelicanparts.com/uploa...1577923316.jpg

BOO!

Borescoped headers and perfectly round!

BOO!

Borescoped Fabspeed cat back and muffler. Perfect!

BOO!

Here’s a shot of the compressor using borescope. BTW when I received rebuilt Turbo there was zero play radially and axially! Smooth as butta. No change in performance from first install to 1000 miles of driving.
http://forums.pelicanparts.com/uploa...1577924849.jpg

Mike G.

Let’s say I did have a serious intake leak would the vacuum gauge read more than the 17in hg I see currently?

Mike G.

There have been some rare cases where the cat pipe has collapsed between the downpipe and the cat, leading to boost issues, which your ping pong ball suggests may be an issue. Clogged cats as well. Have you checked for those, as Nize says?

Also, the stock blow-off valve frequently fails. I would suggest getting a good quality aftermarket one to eliminate that variable.

It is still possible that the cat pipe has a reduced cross-section area close to the CAT. It was difficult to get the camera all the way to the CAT. However I did finally get the camera all the way to the CAT and could see the mesh. I either need to cut the pipe off close to the CAT or purchase a test pipe. I might cut the pipe tomorrow and see what gives! Need to purchase a welder next!! hehehe

Brand new stock one!!! BOO!

Thanks
Mike G.

Duh! Sorry, J-boot is ahead of turbo, so any leaks there will just draw in unfiltered air and cause AFM-reading issues. But not leak boost.

Epoxy or aquarium-grade silicone will seal CV and IAC leaks nicely.

One area that hasn't been examined is intercooler. It can collect LOTS of oil over time, especially with worn-out turbo. Take it out and flush with solvent backwards.

Also, design defect from Porsche is tapping boost-pressure BEFORE intercooler. Better to tap into intake-tract AFTER intercooler for boost-signal to control gauge and wastegate. Problem with before intercooler is it doesn't account for boost-drop through intercooler. This can be 2-4psi and results in dropping boost with RPM because it doesn't account for drop through intercooler.

Even with Tial wastegate, you end up with 2-3psi drop in boost in upper-RPMs because boost-controller isn't aware of variable boost-drop through intercooler (higher psi drop in upper-RPMs). I've got datalog of boost with Tial somewhere. You don't see the boost-drop on gauge because most gauges are fluid-filled or have damping and doesn't show the drop.

"Just ran a test pulling 15in of vacuum on the WG hose to help keep the WG valve closed. Makes a huge difference. Can reach 2 BAR absolute easy!!! Tried to keep it to 1.8 in 1 ,2, 3 gears. Makes me think the WG is the culprit!! BOO!!!"

Mike if the WG being pulled shut (Vac) gets you 2 bars easy (14.7 psi) then I would say you have enough air flow thru the system to make 2 bars...
The Wg is letting go. If you read my WG test thread you will notice that my shimmed WG starts to open at 22 psi applied to the valve (from the exhaust side). If you have pinched off the line to the WG then you have removed the KLR control. The only thing opening the WG is the exhaust pressure.
I am at this point trying to figure out what that pressure should be...
Obviously the turbo in series with the exhaust puts some back pressure. I am going to go for loud test..
Straight pipe from before the cat, and see what pressures I get at the WG.
will post in my WG test thread.
Sox

Thanks guys!

I'm going to do that same test that you did on the WG Soxnail and I'll also check the IC for clogdness.

Looking forward to hearing what the backpressure is without the CAT and stuff.

Thanks
Mike G.