MildMax951

Whoops, make that 0.5 psi for every 1000 ft increase in altitude, problem is I think and work in bar, eg ambient here is 0.83 bar.

Rob

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica"> So getting back to this thread if someone living at 5000 ft using a mechanical guage wrote in said his k26/6 held 11.5 psi @ 6000 rpm, I might be encouraged, but in reality his 11.5 and my 9 psi ABSOLUTE (ie reffed to seal level) are actually the same thing. Am I talking a load of rubbish, or is this correct? </font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">You are correct. While the do make absolute gauges, most (if not all) of the gauges that people use are not absolute. That is why in my post I stated ~9-10 psig, the g references a gauge pressure (referenced to local atmospheric pressure). This is also why I run my EBC set at ~18 psig, or roughly 15 psi sea level equivalent.

Rob

jchaley

You are correct in your assumption. Lots of things are different at altitude. The mechanical boost gauges are differential pressure gauges, the factory gauge is referenced from the sensor in the KLR and is absolute. You will notice that if the car is not running but the ignition is in the run position the factory gauge does not sit at 0 at altitude. It takes almost 3 psi just to get to sea level air density. This also holds true for engine compression tests they will be about 15-20% low at 5000', Idle vacume will be lower as well. I am sure this has caused people to thinsk they had engine problems when nothing was wrong. Off boost a 2.5L 944 engine at 5000' looks like a 2.0L engine with 6.4 to 1 compression
at sea level.

john

Danno

I think the primary factor with the stock turbo holding boost is the wastegate spring. Others have gotten the stock K26/6 to hold a flat 15psi boost curve all the way to redline with an aftermarket wastegate.

With our dualport+spring upgrade for the stock wastegate, the opening pressure started at 14psi vs. the stock 4psi. This allowed us to program in a rising boost-curve in the AVC-R to combat the dropping torque curve. Boost was set at 15psi in the mid-range and went 16psi@5000rpm to 17psi@6000rpm. However, we saw turbo outlet temperatures in excess of 300-F and there wasn't any improvements in the torque curve even with higher-boost.

The other thing too is that for those with stock boost-control, there's nothing you can do about the high-altitude boost-drop. Since the KLR just outputs a pre-programmed duty-cycle curve, it doesn't have any feedback on actual boost acheived and it doesn't correct its signal to yield the desired boost.

GaryK

I live in the Denver area also. My car with a Garrett T04E-46 and a rebuilt/shimmed stock wastegate will hold 16psi to redline, probably more if I wanted to. My old K27/6 would not hold more than 11psi with the same wastegate. And there is a bit less lag with the Garrett.

MildMax951

In summary, we have it from 3 independant list members (Rob, Rage2, GaryK), the k26/6 cannot hold more than 8 to 9 psi (absolute) at high rpm at high altitudes, no matter what wastegate and boost controller you use.
I wasn't expecting to be able hold 15psi (abs)
and fully understand that it would be pointless due to the low efficiency of the k26/6 in that flow range (even at sea level).
If you could get an extra 2.5 to 3 psi ie 10.5 to 11 psi (abs) it would be worth it and I would go down the dual port road, but sadly it looks like at high altitude, that is never going to happen.