That is why you never inject into the intake tube like that. All it took to cause that was a little puddling and even the slightest backfire. I've never done nitrous and I know better than to do it that way. The only semi-safe way I've seen it done that is similar to that was an adapter that put it right on the top of the filter. It atomizes pretty well like that. The way they were doing it, it was lucky to atomize at all.

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2002 Volkswagen Jetta GLI 24V VR6 6 speed
1998 Ford Taurus LX 3.0 Vulcan OHV