Canceling out pumping losses of throttle governed engines

[Kevin Johnson]

Route the exhaust outlet to a low pressure area of the moving vehicle that will not enter the cabin. Route the intake to a high pressure area of the moving vehicle.

[dcb]

hmm... or if you have a low pressure area with no immediate plans to fix it, take your intake air from there? It could "detune" the engine the faster you go and allow larger throttle openings at lower speeds than normal and "maybe" reduced crankcase pressure.

Anyone know the effect of ambient pressure on a typical bsfc map?

The "oval" doesn't happen to move right with lower pressures by any chance?

[Kevin Johnson]

Originally Posted by dcb

hmm... or if you have a low pressure area with no immediate plans to fix it, take your intake air from there? It could "detune" the engine the faster you go and allow larger throttle openings at lower speeds than normal and "maybe" reduced crankcase pressure.

Would venting crankcase gases into this type of system possibly affect emissions?

Originally Posted by dcb

Anyone know the effect of ambient pressure on a typical bsfc map?

The "oval" doesn't happen to move right with lower pressures by any chance?

SAE.org has many thousands of tech papers with searchable abstracts. That would be an excellent place to start.

When I was reading through the 500 last night I ran across several that were related to other interests of mine and I filed them. SAE charges a fairly reasonable $15 per downloaded paper if you are not a member. There might be a local university library that you could visit that has a subscription to the various journals so that you could read them at no charge.

The NACA archives contain many thousands of papers that can be downloaded free of charge but obviously the information is dated.

[Kevin Johnson]

Originally Posted by aerohead

would the vacuum below an ascending piston be any better than a vacuum above a decending piston?

Yes.

[dcb]

Originally Posted by Kevin Johnson

Would venting crankcase gases into this type of system possibly affect emissions?

I wasn't going there, just the intake, at a spot that is already low pressure so little aerodynamic penalty.

Originally Posted by Kevin Johnson

SAE.org has many thousands of tech papers (@$15 apiece)

I think it would be far quicker and more affordable to just hang a vacuum hose off my rear bumper and see what my mpguino says about mpg at a given speed with/without vacuum You could read thousands of papers for much time and money and still come to the wrong conclusion. I just wondered if anyone had done such an experiment under fairly controlled conditions.

[Kevin Johnson]

Originally Posted by dcb

I wasn't going there, just the intake, at a spot that is already low pressure so little aerodynamic penalty.

Lots of pcv systems out there with different locations of the port in the tract. Ever hear of stand-off?

Originally Posted by dcb

I think it would be far quicker and more affordable to just hang a vacuum hose off my rear bumper and see what my mpguino says about mpg at a given speed with/without vacuum You could read thousands of papers for much time and money and still come to the wrong conclusion. I just wondered if anyone had done such an experiment under fairly controlled conditions.

Your last sentence is why you should be searching the abstracts, which is free.

Yes, you could read thousands of papers for much time and money and come to the wrong conclusion just as you could come to the wrong conclusion by hanging a vacuum tube of indeterminate size off your rear bumper trying to simulate an intake tract.

[dcb]

I know enough to consider the size/length/texture of the tube. And will come to the wrong conclusion much more quickly and inexpensively that way

And of course the SAE paper could be faulty too, or be making assumptions that are not valid in a "hypermiling" scenario.

If sae didn't charge I would use it gladly. But I do not know that they can even answer my question, I do know that I can.

[dcb]

Anyway, I think pressurizing the intake is generally counter "eco", in the general sense.

Assuming you are cruising on the hiway in a "typical" car, you have way too much power to begin with. You probably are not in the peak bsfc zone. Increasing the density of the incoming air means the throttle is more closed, and the pressure drop across it is larger.

So in lieu of putting in a smaller engine, one strategy is to detune the engine, i.e. hai. (along with gearing and aero and etc). Bring peak torque down and open the throttle more. If the crankcase is a "closed" system, reducing pressure should affect the air mass in the case as well.

Though if you are taking air from an already low pressure spot, it adds to the pressure differential of the vehicle, to reduce the internal drag of the engine. Don't know if that is a wash or not.

If I had to guess, I would think that reducing crank case air density would move the bsfc peak up the rpm band. But could not sufficiently explain it.

[Superturnier]

Would a smaller diameter piston be better, since there would be less area for the vacuum at the top of the piston?

So a "long stroke" engine would be more economic?

[Alex99]

I've seen a low budget solution on the web and multiple froums that uses intake manifld vacuum to evacuate the crankcase. Its called "Krank vent" and is basically 2 special checkvalves that are used in the original PCV system.
Do a search in the web and you'll read more. I'm also still investigating if this is a good solution.

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