All stock...
Sox

Well looking in the turbo manual...
My back pressure is too high. It should be : Edit maybe not...more research would indicate that the ratio mentioned in the manual is to be expected at specified rpm and boost only. Higher rpm and or boost will produce different (higher) ratios.
Sox

http://forums.pelicanparts.com/uploa...1580242450.jpg

I measured where the manual shows. But I still also have 22-25 psi BP with only 9 psi boost. But like you said my values were from a gauge and only show the max values as I was squinting down at the gauge.

Thanks
Mike G.

It would be nice if someone had a decent DA system and could show the data for a stock engine. But I've searched to no avail. I give! Uncle!

Mike G.

Mike don't throw in that stinky towel yet :)
As far as I can tell, back pressure varies all over the place, with heat being the other variable.
As the rpm of the turbine climbs the back pressure drops. So initially it could be as high as 1:4.
At a constant rpm and load it settles down to any where from 1:1.2 to 1:2 ratio.
My issue was that the WG was weak (as proven by the vacuum attached to the WG control port).
You need to figure out if there is enough charge from the turbo first.
Lets eliminate one other thing, oil blockage in the inter cooler.
Hook up a barb in the line coming from the banjo bolt to the CV and put a gauge on it that you can see while driving. Pinch of the part of the line that goes to the CV, run your test again, the 2 numbers should be very close with the banjo bolt leading slightly. if this is the case then we can eliminate the oil in inter cooler hypothesis and move on to next.
Sox

BTW the test with the spring arraignment worked, got 16psi or so. The spring however did not survive the test.
Sox
Ps. the over boost error kicked in and put the car in limp mode.

There is not much info out there that is specific for turbo back pressure for us.
The gist of what it boils down to:
1:1 perfect.
1:1.5 borderline.
1:2 get a bigger turbo.

I am in the process of adding exhaust pressure monitoring and logging simultaneously with boost, AFR and RPM.
Will keep y'all updated.
Sox

Well that's a relief!

Mike G.

Mike did you run the pre inter-cooler pressure test?
Sox

Not yet, probably this weekend after I put the car back on the ground. Oh yeah and install a microwave, have a BBQ, fix my wife's shocks and brakes and anything else she comes up with :p!

P.S. I now wish I would have bought a zeitronix system instead of just a few gauges. I knew I'd say that later :mad:.

BTW I'm also going to completely block off the WG with a plate.

Mike G.

To your first item "Honey thou shall do" :)
If you block the WG...you better have quick reflexes, so you can get off the gas if your boost heads north. If all is working with your turbo and inter cooler it will and fast.
Sox

oh man, if you block the wg you may need to replace the head gasket...

I would think it would have the same possibility as pinching off the WG control line except that there is no chance of leaking past the WG!!! Porsche actually states to pinch off the WG control line for a test. Maybe there is a big difference between the two??

Mike G.

Nope with the pinch test the exhaust can still push the WG valve open before the engine goes...
If you block it off then there is no escape for the exhaust other then the turbo, so you get the positive feed back loop...mor exhaust more boost, more boost more exhaust till some thing (head gasket) gives.
That's why I was suggesting quick reflexes.:)
Sox

I keep forgetting that the 944 WG gets pushed open by back pressure too!! DOH! I'm not used to seeing that config for a WG!

Mike G.

I'm sure my koala like reflexes are up to the task ;)!

Mike G.

Ran the test for back pressure and boost...just with mechanical gauges at this point, waiting on a sensor and some components to do the full logging run.
-In second gear at 3500 rpm about 10 psi boost and 13 psi BP.
-In third gear 3500 rpm about 11 psi boost and 15psi BP.
-In forth gear 3500 rpm about 12psi boost and 16 ish psi BP.

Did not do a fifth gear test..too many of our finest out right now.

If I let the car go past 3500 rpm then it peaks at about 13psi but the BP continues to build about 20 psi ish.

Obviously the figures I reported in my previous post were wrong. :(

Will get more definitive numbers when the stuff comes in.
Sox

this is actually a good config, as it provides a failsafe when all else fails.

Me comprehenday! but I keep forgetting from the setup I'm used to seeing.


Thanks
Mike G.

That doesn't sound too bad, well as far as my drunk a$$ can tell!!


Thanks
Mike G.

keep in mind the wastegate pressure is the spring pressure +/- intake manifold pressure as determined by the cycle valve. this means as more boost is created (higher intake manifold pressure), higher exhaust pressure is required to overcome the (spring+increasing manifold pressure) so the exhaust pressure will increase (exponentially?) as boost increases, until redline or ignition cutoff.

My test were done with line to WG pinched off.
Sox

I think that's backwards? Higher manifold pressure opens the WG valve?

Thanks
Mike G.

HA! just noticed the above post was at 9:51!! hahaha not intentional.

Mike G.

Stupid a$%^ sensor showed up dead....
Teach me to buy from amazon.
Sox

that's what the cycle valve is supposed to control.

My understanding is the the CV does not use any manifold pressure feedback? It's just a set duty cycle based on something RPM?, TPS blah blah. All of this stuff seems like circular reasoning to me after a while.

Thanks
Mike G.

Mike The KLR controls the CV based on TPS and manifold pressure.
Sox

Ran the test with shims in and exhaust system checked for blockages and leaks. (Old CV was dead so new CV in the car).
Results:
-max boost 10.72 PSI, @ 3500 RPM.
-The back pressure with the CV controlling the exhaust bypass was max 15 psi.
The log is posted below. Sorry no log for back pressure yet waiting on sensor.
Sox

http://forums.pelicanparts.com/uploa...1580931248.jpg

Pretty close to what the manual states??

Mike G.

Pretty much 0.72 bars boost and 1.02 bars back pressure. 1 : 1.39 ratio.
Sox

As soon as I get the new sensor will run the BP to boost test again. I believe after the 10 psi point the back pressure rises much faster than the 1: 1.4 ratio seen till then.
The turbo goes into "beating the air" rather moving it mode.
My turbo is original and has 250k on it, so it may also have age issues. It turns easily and there is no play that I can tell, but it may be time to get is refurbished or get a new one.
S.K

250k???? Wow!

Yup had it since new in 86'
Sox

Just ran with 3/8 shim. Stock gauge finally hit 1.8 bar at about 4000 RPM then started tapering off pretty quickly. I wonder if its WG bleed off or Turbo charger not being able to keep up with mass flow at above 4000 RPM?

Thanks
Mike G.

I might actually try this as I shimmed the hell out of the WG 3/8" and still not over boosting. BTW won't the over boost protection keep the boost from going too high?


Thanks
Mike G.

Nope the only way KLR can control boost is by using the WG. If you block it off there is no control.
Sox

Need to find out why you are not getting boost.
The k26/6 turbo as used in this car is at its most efficient at car rpm of 3500. The WG even with shims will start to bypass at 20 or so psi back pressure. So with the line to the WG control pinched off, it should not let the BP go over 20 to 22 psi. If there is that much BP and low boost then there is another issue.
As you have checked the turbo for free motion and minimal play...
You have also checked the BOV (which in our cars is really a by pass, and not a blow off)....
Have you checked the pressure prior to the inter cooler ?

I am assuming the first 2 and waiting to see what you get for the test.
Sox
Ps. also to keep you from going banzai on your engine :)

are you 100% certain there is no leak in the intake system? you could try blocking off the BOV to test if it's working properly as that's one component that can bleed that much boost in a hurry.

there could also be some kind of cut or split in one of the intake hoses that allows it to hold some boost and then all of a sudden will bleed air, are the intercooler hoses okay? throttle body hoses? j-boot? there's a lot of places where a small cut or split or even a loose connection/clamp will be hard to detect.

btw, it's safer to first check your intake is all tight and leak-free before focusing on the exhaust, because if you have a leak in the intake there's no way the turbo can ever spin fast enough to make boost so you could accidentally over-spool the turbo and grenade it. ask me how i know (it happened to me).