Quote:
Originally Posted by chevota84
I get that, but we're using it to monitor a setup that's in use, not engineering a turbo from scratch. Since you rarely see under 1:1 at wot we should able to use that number as an estimate of overall effeciency even though it won't cover every eventuality. You've seen a lot more turbos than I ever will; when would a 2:1 setup be efficient and a 1:1 wouldn't be?
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It is honestly such an arbitrary number that it depends entirely on what you are doing, what wheels they are, what you are after with the truck, etc... For instance: Let's take an HX60 into account. In a scenario where the front side of the thrust is getting trashed consistently with 2:1 on an over the road application you want to get drive pressure down for pure reliability. Obviously the turbine forces are so far outweighing the compressor side that it is breaking through the oil film on the bearing and trashing it. The same turbo in a competition setting you WANT that high drive pressure in most cases to keep the thing lit at the end of the track. OR look at it this way: let's say that 2:1 drive is with a 3.4 turbine vs a 3.6. The 3.4 may not trash the thrust with 2:1 as opposed to a 3.6 as the 3.4 may apply less thrust load than the 3.6 with the same drive pressures. The next thing you have to think about and take into account is why the drive pressure is there. Is it because you are physically choking it with too small of a turbine side or is it because you are requiring so much shaft hp to maintain the demands of the compressor side (be it side or pressure or both) that it just takes that much drive pressure to achieve your goals?
Long story short: drive pressure is for tuning a setup if you know the parameters you are after. Past that don't worry about it unless you have either reliability issues or issues staying on top of the turbo.