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.