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swapping out a VNT15 for a VNT25

Time:2018-01-06 16:45Turbochargers information Click:

It's a more complex question than it seems on the surface. Matching turbos to engines is a pretty involved process. You need to match the displacement, number of cylinders and desired power output of the engine to the size of turbocharger that will operate in the most efficient part of its "map" under those conditions. A stock 90hp TDI is perfectly matched to the VNT-15. Wett chips or a tuning box push the little turbo closer to the upper limits of its performance, though chips or a TB alone won't hurt it. Start messing with a lot of other mods, especially the VNT adjustment mod, and you can spin the turbine too fast and the turbo will fall down go BOOM. The general consensus is that 18 psi sustained boost at sea level is a pretty safe, conservative maximum on a 1.9 liter TDI with the VNT-15. Higher boost would require a bigger turbo and intercooler for efficient operation.

Bigger turbos have more turbo lag. That would be the first thing you'd notice. And a VNT-25 could easily blow a 1.9L TDI's cylinder head into orbit without even breathing hard. You'd have to throttle it way down to stay within the engine's tolerances. The only point I can see to that mod would be for extremely high altitude operation. One thing I'd eventually like to do is to have a bigger compressor wheel and turbine installed in mine so it'll make full sea-level boost up here in the mountains without spinning too fast.

-mickey

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