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Variable Nozzle Turbos - Why are they not widely used in the aftermarket ?

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VNT's not seen in our field, although modern standalone ECU's could easily control them ?

Very good question!

Probably the price premium that would be charged would put many off the idea, but I would think it had a lot of advantages for a 'street' driven vehicle.

In theory, I expect aftermarket ECUs could be configured to control them, but I'm not aware of any that do that natively? Do any of the guru's know of examples that are able to control the VNT in the supplied s/ware/

The other aspect may be that many/most aftermarket applications are specifically for "power', with the engine operating in a relatively narrow rpm range, and the compromises of the VNT at peak flow is of much greater concern than low rpm gains in power and response?

Then again, how many "tuners" are able to optimise the overall performance tuning with a fixed design, let alone with the further complication of another variable?

I've done it just over 20 years ago on a 2 liter Subaru WRX gas engine. Control was easy. The turbos are bulky, heavy, and don't cater to performance. It was a novelty, but in my experience couldn't compete with a performance turbo catering to gas engines. They make sense to me for diesel use though.


Can you elaborate why a diesel is better suited ?


When I first learned about these turbos years ago, it sounded like a magical thing. Why wouldn't we want to be able to vary exhaust A/R dynamically? In practice, the range of behavior has not been as big as I hoped, and it made sense once I started doing back to back tests of fixed housing swaps.

There is still some benefit, but the weight, size, complexity, reliability of the physical systems are a concern. Diesels are heavy anyway, and they operate at lower EGT generally than gas engines, so the systems tend to hold up better. I also suspect since diesels are less commonly used for short trip driving, the variable system isn't getting heat cycled as much per mile. Conceptually I also like it as an option to impact engine output, exhaust heat and pressure without varying fueling on a diesel.

The best implementation I've personally experienced on a gas engine is the Porsche 911. Porsche has fantastic engineering and it's an expensive vehicle so certainly not a cheap implementation of the technology, and still when you swap out the stock VGT turbos for quality aftermarket performance units, it's a net performance improvement in my opinion.

Another advantage with the diesel engine is they can be used as exhaust brakes, by closing them right up, or progressively for over-run speed control on downhills.

Thank you both.

Thanks for bringing it up Dom. It's one of those things I wonder about every few years. I have a hunch if Garrett for example, set out to make a G series VGT turbo specific to racing that it could be great. In the meantime, as long as we are comparing OE turbos to aftermarket racing units, the VNT/VGT ones are held back by OE constraints.

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