Quote:
Originally Posted by p_b82
With VNT rather than twin turbos it is easier to keep emissions down if you get the fuel mapping and vane control right-
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The issue with a vnt big enough to provide good top end without crudely overspinning it (like one french manufacturer whose cars suffered lots of turbo failures before it was revealed their map overspun the turbo) is getting it going whilst keeping it clean.
The mappers (word used loosely) tend to chuck in more fuel to get it to spool, and they often smoke a little (or a lot) whilst they build boost.
A twin turbo setup on the other hand usually has the small turbo boosting at 1100rpm, crossover around 2500rpm depending on setup and still good strong boost at the high end of the rev band without excessive emp and or emt.
The twin turbo setup typically produces more power for longer with higher ve .
In view of this I struggle to see how a turbo with a smaller window 'is easier to keep emissions down', tyhe manufacturers work hard on emissions regardless of single, twin or triple turbo setup.