K04 vs. K04/K16 Hybrid. --->
06-23-2004, 08:43 AM
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K04 vs. K04/K16 Hybrid. --->
In view of the many questions recently asked about this topic, here are some thoughts (IMHO) to check out.
A little physics. Sorry.
The <b>flow power</b> required to push a given air flow at a given boost is equal to the boost pressure times the volume flow rate. This power (and more, because of losses) is provided by the compressor wheel in terms of turbo shaft speed and torque (shaft power), as created by the <b>turbine wheel</b>.
If the compressor wheel is enlarged to produce higher boost and flow rate (flow power) at the same speed, then the turbine will be required to produce simply <b>more torque</b> at the same speed. How to extract more torque at the same speed? More exhaust flow on the turbine blades --> More inlet pressure into the turbine --> More backpressure (with given exhaust) for the engine ...... Backpressure? HELLLOOO!
It gets even worse, if the compressor wheel is enlarged to produce the same boost and flow rate (flow power) at <b>lower speed</b> (reliability). Then, the turbine must produce that power (and more, because of losses) at <b>lower speed and higher torque</b>. Yet greater backpressure would be created.
Turbines, like compressors have maps with efficiency islands. Turbines and compressors are carefully matched for each engine to operate within those efficiency islands. To stray too far on either side of a turbo is not good. Bigger is not always better.
That said, I'm sure there'll soon be data to "prove" the opposite. :-)
Happy Motoring !
A little physics. Sorry.
The <b>flow power</b> required to push a given air flow at a given boost is equal to the boost pressure times the volume flow rate. This power (and more, because of losses) is provided by the compressor wheel in terms of turbo shaft speed and torque (shaft power), as created by the <b>turbine wheel</b>.
If the compressor wheel is enlarged to produce higher boost and flow rate (flow power) at the same speed, then the turbine will be required to produce simply <b>more torque</b> at the same speed. How to extract more torque at the same speed? More exhaust flow on the turbine blades --> More inlet pressure into the turbine --> More backpressure (with given exhaust) for the engine ...... Backpressure? HELLLOOO!
It gets even worse, if the compressor wheel is enlarged to produce the same boost and flow rate (flow power) at <b>lower speed</b> (reliability). Then, the turbine must produce that power (and more, because of losses) at <b>lower speed and higher torque</b>. Yet greater backpressure would be created.
Turbines, like compressors have maps with efficiency islands. Turbines and compressors are carefully matched for each engine to operate within those efficiency islands. To stray too far on either side of a turbo is not good. Bigger is not always better.
That said, I'm sure there'll soon be data to "prove" the opposite. :-)
Happy Motoring !
06-23-2004, 08:53 AM
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Careful though, you're bordering on "techno-babble". Without the turbine
maps you don't give a sense of proportion to these effects. No one here even has an idea of the turbine inlet pressure for K03s, K04s, or whatever so its sort of begging the question.
With this lack of information the only solution is to test. And that is very much acceptable "proof". These ideas have been discussed a lot in previous posts but it was up to Verruckt to install them and try them out. On pump gas he ran a 3.8sec FATS time(stock ICs even!). Most APR pump gas cars on K04s run around 4.5-4.7(if they're lucky).
Definitive proof->nope. Possibility implied->yep.
I'm not being argumentative though, just giving a different perspective.
With this lack of information the only solution is to test. And that is very much acceptable "proof". These ideas have been discussed a lot in previous posts but it was up to Verruckt to install them and try them out. On pump gas he ran a 3.8sec FATS time(stock ICs even!). Most APR pump gas cars on K04s run around 4.5-4.7(if they're lucky).
Definitive proof->nope. Possibility implied->yep.
I'm not being argumentative though, just giving a different perspective.
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06-23-2004, 08:58 AM
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Usually is the case, but not this time. ;-) They're very valid concerns. But they
have been discussed before as well, to the point that Chris(Verruckt) as a working mechanical engineer on turbo diesels felt it was a legitimate experiment to try. And got some decent results.