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      12-14-2013, 05:18 PM   #96
Boss330
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Quote:
Originally Posted by solstice View Post
The anti-lag system operates on-off-on throttle it does not help from idle rpms. Here you you need small turbos to get on boost quickly. My guess is small turbos and that in a strive to keep as much as possible of the M high rpm character they use most of their potential to pump air at high rpms but your guess is probably as good as mine here.
My guess is also "small" turbos, just as on any other modern turbo engine. But with a bit more margin for safety and durability than what you assume, i.e. not running at 95-100% of maximum in stock tune...

Do we know everything about how the anti lag system works, and that it is only operative during those conditions?

But anyway, look at RS6 spec, F10 M5 spec and notice how soon they build pressure (and power) from idle. And both have been tuned to increase power by 25% on stock turbos. Let's say that the S55 relatively has slightly smaller turbos, should still be able to do a 20% increase. Which brings us to 515hp, or +85hp.

And a turbo also consists of both a compressor and turbine unit. Turbine unit can be small to aid spool up. But with a good wastegate it can bleed off excess exhaust at high rpm's to avoid backpressure and overspooling. The compressor unit needs to flow a decent amount of air, and since BMW has said that the S55 shall make it's 430hp also in low density, high altitude and high temp situations I suspect that the compressor unit is able to flow decent amounts of air. If you tune it to 520hp, sure it might not make that power on the hottest day in Death Valley or at Mount Everest altitudes (like the stock S55 shall at 430hp). But that's part of tuning. If you push the envelope to 95% at ideal conditions, you won't get the same power under less ideal conditions.

To me the turbine unit looks fairly small, but notice how the wastegate is positioned and the large diameter of the exhaust part that routes exhaust past the turbine. To me that indicates exactly what I said above. A small turbine to aid spool up, but a large exhaust bypass to exit exhaust outside the turbine at higher rpm's. The compressor unit on the other hand looks fairly big.






Last edited by Boss330; 12-14-2013 at 05:30 PM..
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