Having used two different exhaust pressure test kits, and having found NO back pressure (according to the two gauges), I am left wondering if this is abnormal or even possible?
I expected high back pressure but have measured none. Even at 2000rpm.
I made triple sure that the adapter was in the manifold securely every time and it was a real PITA. I’m sure I did a good job and left no escape for the exhaust gases.
So how “normal” is it to have NO exhaust back pressure?
Engine seems to run fine. With one exception.
I read the article. Thanks. It’s funny. I have read as many or more expert articles which say any back pressure is “bad” pressure.
Personally, I find it difficult to imagine how there could be ZERO back pressure at the exhaust manifold of any running vehicle regardless. At leas 1 or 2 psi I would think.
Well designed exhaust can easily have zero backpressure even well up into higher loads. Backpressure creates a bit of an EGR function. Not desired for high horsepower.
Exhaust backpressure can go negative as well. Pulses from each cylinder can creates pressure waves that go negative. Street exhaust systems can draw fresh air into the exhaust to make a more complete burn. Cars in the mid to late 70s had these check valve systems. Race cars use the negative pulses to scavange the crankcase pressure for better ring seal.
If gas is flowing, on average there’s a pressure drop, which equals backpressure. Maybe not much, not enough to worry about, ‘practically zero’, but not zero. Without a pressure drop there would be no flow.
edit-We are talking about a stock car with a cat and muffler here. Not a set of open headers.
And on a recent Engine Masters, every time they reduced the resistance of the exhaust system (reduced the back pressure) they made more hp. Maybe some combinations produced more power than others with a longer pipe, but that doesn’t mean there was zero back pressure.
Engine Masters did a thing on back pressure and talked about the pressure waves…
I understand it, but I know Mustangman understands it wayyyy better then I ever will… lol
I presume you were testing at the o2 sensor port in front of the cat. You could test at the other one, behind the cat. Might provide a clue. according to below, normal backpressure is normally quite low, 1 -3 mmHg, even at higher rpms. Maybe your gauge isn’t sensitive enough. In any event, it seems like you’ve pretty much eliminated a clogged cat as the cause of the engine overheating. The cat could still be not be doing its job at eliminating pollutants of course. And that could possibly confuse the computer’s calculation of the air/fuel mixture.
