toddk911

"So you got a Tial and can't hold the boost either."

A few guys have swithced from the GURU to Tial and realized the smae thing, unfortunealtely, it's the turbo running out of steam, not the wastegate.

hosrom_951

toddk911: Sorry for saying that is was you that was running a K26/8 and holding boost to redline, but i do remember someone(actually more than one) holding the k26/8 to redline with a GURU wastegate as well.

Alpine951

toddk911 says:

"it's the turbo running out of steam"

But I disconnected the reliaboost and plugged up the hose coming off the intercooler pipe and I was able to make 15+ psi way up into 5500 rpm. Doesn't this show that the turbo was able to make the boost?

Jake951

Yes, I am one of those people who made the switch from a Guru WG to a 38mm Tial and saw no difference in the upper rpm's with a K26/8. The boost dropped from 18 psi peak to 15 psi at redline with both WG's.

I did the test of disconnecting both WG's from the boost controller to see if the boost still dropped at the top end. At WOT with no boost control at all (you have to do this carefully!), the boost still dropped to 15 psi at redline, so it has to be the turbo that's running out of steam.

Alpine951

but if I was able to hold 15 psi uncontrolled then I don't get how the answer is that the turbo running out of steam is why i go from 18 to 10 when its controlled.

hosrom_951

Because the wasegate valve is always closed when you plug that vacuum line, thus giving the turbocharger everything it's got i guess??

Mike1982

I have a reli-boost control. I always thought it was the turbo just running out of steam. I plan on upgrading that in the summer anyways. If anyone has a testpipe to sell, Bursh, just let me know. I am in the market for one!!

Danno

"but if I was able to hold 15 psi uncontrolled then I don't get how the answer is that the turbo running out of steam is why i go from 18 to 10 when its controlled."

If you noticed that in order to hold 15psi with the wastegate line disconnected, you had to gradually increase throttle with RPM? Similarly the boost-control signal going to the wastegate also has to vary with RPM as well, but there's no way for a mechanical controller to do that. See diagrams I've written up here: Wastegate okay, now what?

One experiment I did a couple years ago was with a pressure-regulator type of boost-controller. On a full-throttle run, I would have one hand on the controller and would give it a 270-degree twist as RPMs increased. What I was doing was cutting down on the pressure going to the wastegate to close it down more and more with RPM to increase boost to compensate for exhaust-pressure. This then resulted in a flat boost-curve.

What happens with big-turbo upgrades is that exhaust pressure is STILL creeping open the wastegate at high-RPMs, but the higher flow-capacity of the turbo compensates. With the K26/6, you can hold flat boost, but that requires a controller that reads RPMs and measures boost and exhaust-pressure (indirectly). Only an electronic controller can do that and that's been the only way I've been able to hold flat boost with the K26/6. I was actually even able to dial in a rising boost curve, from 15psi in the mid-range to 18psi by redline to compensate for the dropping torque.

Another interesting artifact with manual controller is the difference in boost-drop with different mid-range max-boost levels. WIth max-boost set to 15psi, the drop is typically down to 13-14psi. But if you increase max-boost to 18psi, the drop gets larger to 12-13psi, strange. You figured it would only drop down to the previous 13-14psi. I think this has to do with the higher boost leaving more residual pressure trapped in the line between the controller and wastegate, thus causing it to close slower and leak more boost.

In your case, the drop IS a little more than normal though, so I suspect the turbo may be on its way out.

TheMoldyCow

It also drops like a 2 ounce weight...

hosrom_951

Danno: Which EBC did you use for the k26/6 to hold boost to redline?

toddk911

Could someone make an EBC with just an electronic pressure switch? Or is there a lot more to it then that?

Like a pressure switch you would use for a water injection system??

hosrom_951: Is that a new pic for your avitar??? Nice!!

hosrom_951

toddk911: Thank You, yes it's a 'new' pic