Found this info from Neuspeed. Neuspeed is a highly respected tuner in the VW/Audi world.
Quote:
The K04 is designed to provide reliable, long-term service as long as its performance parameters are not exceeded. Driving the car at engine speeds above 5800 rpm with 15spi or greater boost significantly increases the exhaust temperature measured inside the K04 turbine housing. This signals that the maximum efficiency of the turbocharger has been exceeded, and that the energy produced by the turbine housing is now converting to heat rather than accelerating the compressor wheel faster. Unless a careful and extended idle-down is performed at the end of every hard driving session, the rapid heat build-up from high boost/high rpm operation causes the turbine shaft to soften, and allows the inconel turbine head to droop. The result is an imbalance that ultimately leads to a shaft failure.
this is why our engines are severely limited (peak hp and torque at 5200 rpm) above 5200 rpm. there is a mandatory wastegate opening to prevent the turbine from over speeding, which is what the real main concern is.
I'd like to offer that with hundreds of PPC Tuners in the field, we've yet to see a turbocharger failure at boost pressures above 15 PSI. The VW application cited here may not be directly comparable.
However, in comparing notes with GM engineers, we have determined that anything over 325-ish engine HP worth of airflow (about 280 WHP) can overspeed the stock turbocharger. More than anything, this seems to be the upper limit of the turbo's durability.
Boost pressure in and of itself is actually a somewhat arbitrary number, as it's not a direct indication of airflow. HP, on the other hand, is a very direct indication of airflow, and in turn, turbocharger speed required to produce said airflow.
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Bill Hahn Jr., Hahn RaceCraft, Inc. Home of the World's Quickest and Most Powerful Solstices
First to the 14's, 13's, and 12's in the 1/4 Mile
12.00 @ 117 MPH Street Solstice World Record
Hahn RaceCraft, Inc.
Turbocharging GM's since 1988 http://www.turbosystem.com
THe power drops off guys, because you are running out of effiency, and increasing boost etc, and tuning it further, just runs the turbo off the map, this is why everyone is making their peak power nearly at the same point until you work with a larger turbo/ But yes this is true of any turbo.
Don't forget not all K04 turbos are the same. There are well over 10 variants of the K04 each custom tailored to the system they were designed for the car they went into with the car company and BorgWarner. Our variant of the turbo is probably modified to be more friendly in the aspects of the boost levels our car produces the others that use the same turbo don't make.
I'm interested in seeing what BTF finds with the one they're tearing apart.
Don't forget not all K04 turbos are the same. There are well over 10 variants of the K04 each custom tailored to the system they were designed for the car they went into with the car company and BorgWarner.
Precisely what I said above about the VW version
We likely have a different unit altogether.
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Bill Hahn Jr., Hahn RaceCraft, Inc. Home of the World's Quickest and Most Powerful Solstices
First to the 14's, 13's, and 12's in the 1/4 Mile
12.00 @ 117 MPH Street Solstice World Record
Hahn RaceCraft, Inc.
Turbocharging GM's since 1988 http://www.turbosystem.com
A free-er flowing Intercooler will lower the boost pressure that the turbo must put out to get the desired boost at the intake manifold. The higher the desired boost and CFM, the worse this pressure difference gets on the stock IC. Our stock intercoolers are designed for 260hp. A better IC will prolong turbo life and lower the air temp going into the intercooler since it puts the turbo in a more efficient place on its map (due to the lower output pressure). An IC upgrade is strongly recommended by Lyndon Wester with his tune.
Never the less, the stock turbo won't put out 23psi at 7000rpm on a 2litre engine, its compressor wheel is just is too small to feed that much CFM.
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Dave at www.DEJONPOWERHOUSE.com
Currently running 311 rear wheel hp with 16g kit at 25psi
Stocking Dealer for HP Tuners VCM Suites and Wester's tune ~~~~~~~~~~~~~~~~~~~ NASSOA
Founding Member #6 ~~~~~~~~~~~~~~~~~~~
In a street driven application, you would have to work very hard to push a tuned GXP to turbo failure. I would be more concerned for the safety of the people around you. The amount of time that you could spend >6000 rpm and > 29 lbs./min. is just too limited in a street application. To be honest I dont see to many track applications where this would come into effect. You would have to spend time at WOT or very near ala NASCAR to put the car in this position. Now if we had an Autobahn.
My other turbo charged vehicle is a diesel truck and in heavy towing situations I run it at 1100*F and greater for hours on end, I have a fuel range of 600 miles. I do use a cool down technique when it has been working under continous loads, however it doesnt take but a few minutes to get the entire system way below safe temps.
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It is Cool, Leather, XM, Monsoon and different! :)
I think that the best turbo for the ecotec is the GT30.
Boost at very low range is not good for internals and transmission, and a bad flow at higher revs is not efficient. The car was made to have a confortable driving with a good response at all gears, very long ratio gears and a lot of torque since 2000rpm, doesn't have an evo or sti feeling, but it's easy to improve that.
The question is that the new 265hp Audi S3 has a very similar turbo and develops about 310-320hp only with ecu tune, arriving even at 340 with mods. I think the stock audi cams and better intercooler flow and head is the answer. Stock ecotec cams are very bad flowing.
GT30 + cams and the Gxp/Redline will be really sports cars, that's I'm going to do.
