It just occurred to me that I actually used the Bernoulli effect in the exhaust system of my race car. It was called a “Pan Evacuation System”. There was a pipe welded into the narrowest section of each collector, with a one-way valve attached and hoses that led to the valve covers. The idea was that the high-speed gasses in the collectors, passing by the beveled pipe openings, would create a partial vacuum and draw a negative pressure in the crankcase. That would aid the piston rings in scraping oil off of the walls and reduce foaming etc. It has nothing to do with the issue at hand but it does support Cabriodad’s theory.
Cabrio’s theory is interesting. It’s a possibility I hadn’t thought of. The same effect that the upstairs bathroom has on the trap of the downstairs sink if it isn’t properly vented could happen with a dual exhaust system. Increased velocity through a restricted I.D. and the resulting drop in lateral wall pressure could create a vacuum in the other pipe.
The plot thickens…I love it.
I had a chance to to try to replicate the reported incident this week with no success. I held a light piece of paper towel against the pipe exit while a friend started the car, reved the engine to ~2000 RPM for a second and then released the throttle (several times). I didn’t see the slightest indication of the towel being “sucked-up” the tube - it was just blown away from the exit. It was a 4-cyl engine with single exhaust. What I did note was that the engine did not return to idle suddenly even tho the operator released it “instantly” at 2000-2500 rpm. I know that back in the early days of exhaust emmissions development, a “Dashpot” was added to the system to prevent sudden throttle return to idle. I think that was because once we moved to “lean-burn” in all of the circuits, including idle, the engines had a tendancy to stall when the throttle was released. Perhaps that was because if the sudden influx of exhaust into the intake, especially with the higher-overlap cams being used. Now I’m rationalizing.
I will have access to a modern “performance” vehicle with Duals this coming week, so I’ll try again.
Maybe we’ll hear something from the guys, during today’s show, of any tests they may have performed.