Hallo zusammen,
hier etwas technische Info fuers "Archiv":
wer ab und zu mal im US Forum Roadfly rumschnueffelt, hat sicher auch schon mal von den diversen in Planung bzw. im Bau befindlichen Leistungsteigerungen mitbekommen.
Insbesondere "John in DC" hat dabei keine Zeit oder Kosten gescheut und faehrt mit einem Twin-Turbo "Monster" durch die Gegend.
Dies kann aufgrund technischer Beschraenkungen ausschliesslich im 5L Motor umgesetzt werden!
Sein Fazit: es gibt keinen Turbolader, der gross genug waere um einen CSi oder gar einen 6.0L Motor bei einem Twin-Turbo Setup bis zur Drehzahlgrenze ausreichend zu beatmen! _Nur_ beim normalen 5.0L reichen die groessten verfuegbaren (und im 8er unter zu bringenden) Turbos aus um im Verbund mit einem sehr effizienten Intercooler, die notwendige Luftmenge zur Verfuegung zu stellen.
Die einzige "sinnvolle" Loesung fuer die anderen Motoren ist ein Single-Turbo Konzept (die Begruendung dafuer verschliesst sich allerdings vor mir). Dieses Konzept wird zZ von ihm weiterverfolgt und es wurde bereits von anderen Seiten dahingehend Interesse bekundet, dass eine Kleinserie (wie auch immer) auf die Beine gestellt werden koennte.
Hier der Originalbeitrag:
Figured this may be valuable to have in the archives...
To begin... The T3 Super 60 posseses the largest compressor that will physically fit in the engine bay of the E31 without performing *major* surgery.
When mated to the five litre motor, the Super 60's will make ~389 HP per turbo at 6000 RPM's while remaining inside of the efficient zones of the compressor. This means ~778 HP of safe airflow at redline as demonstrated by the mapping below...
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Now compare this to the same "physically largest" set of T3's mated to a six litre motor. The same Super 60's will make ~352 HP per turbo at 5000 RPM's while remaining inside of the efficient zones of the compressor map. This will give an impressive ~704 HP at 5000 RPM's. However, since the engine will redline another 1000 RPM's later, the compressor is quickly pushed beyond it's zones of efficiency(aka compressor overspin). Notice in the map below that the 6000 RPM (green) datapoint is completely off the map...
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...this means that revving the six litre motor to redline would likely destroy the engine due to excessively high IAT's (intake air temps). For the uninitiated, compressor overspin causes dangerously high IAT's. High IAT's lead to pre-ignition, detonation, and eventually melted pistons.
The only way to properly fix this is by using a larger compressor which, as previously established, simply isn't feasible. A band-aid fix would be to introduce water or alcohol injection to cool the IAT's at or near redline.
For S70 and M73 users, the problem is the same (compressor overspin) albeit to a lesser degree. I can post maps for those engines if you wish.
After this long diatribe, I hope you can see that twin T3 turbo's simply aren't a viable solution for larger displacement engines.
So what is the solution? In short, the solution is to use a single turbocharger.
Doing so allows enough flexibility to handle all possible V-12 engine variants and still remain in the "safe" zone of the compressor map.
I am currently developing such a system but have not yet decided whether I will make anything available. If I do, you'll definitely be the first to know as you're likely to benefit from it than most others here.
Rgds...
- John
'92 850i Twin Turbo
If by chance you *could* fit the right compressor, the upside given the data above would be a whopping 467 HP per turbo - - or about 934 HP at the crank.
Of course, you'll be running less than 18 lbs of boost so the specific output will also be less. Given my discussions with Henry, your goal was some 8PSI wasn't it? Thus I've created another mapping to demonstrate those datapoints...
As you can see, the datapoint at 6000 RPM's is still off the map - - probably somewhere in te 45-50% efficiency zone - - which is an indication of compressor overspin and thus dangerously high IAT's.
In a perfect world, this is the compressor that I would use for a 6 litre twin turbo setup...
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...just too bad it won't fit. Rgds...
- John
'92 850i Twin Turbo
Hier (Roadfly E31 Board)
gibt es das Resumee nachzulesen.
Gruesse
Reinhard