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Originally Posted by cheekychimp
I...but your compressor might only reach the end of it's efficiency range at 7500 rpms.
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Two points here:
7500rpms are obviously engine rpms. :smile:
These bear little resemblance to compressor rpms, that can peak at ten times or higher.
On top of that, compressor rpms depend on engine LOAD, not just engine rpms, so 7500rmps in 1st gear are a much lower load than the same revs in 6th gear.
That's why some people map their cars 'safely' on the RR using 3rd or 4th gear, then go give it hell on the highway and it blows up. Top gear and aerodynamic resistance create a heavier load for the engine, which in turn forces more exhaust gases than the RR scenario and those gases create more torque on the compressor shaft (leading to more boost at the same revs!)
The end of the efficiency range is not like a brick wall (like the surge line for example!)
The efficiency range more like tapers off, allowing more and more heat to creep in percentage-wise. So there is no sharp limit to avoid, but a general area to shift to.
Also remember that precompressor injection shifts to right not only the efficiency islands, but the surgeline as well, so if it's done too early it can bite back (I've reason to believe it has happened to me, but it's hard to prove)
Cheers,
John