I really want to get all the pro and con reactions to this idea, as well as some tips on how to implement parts of it. I talked to MPG Mike for about two hours last night, and he has about half dozen fairly simple mods that can improve both economy, and performance. All of them raise some concern that must be dealt with to keep things working in a healthy way.

One of those ideas, which I would like to try is to plumb the crank case breather cap so it builds vacuum inside the rank case. This will reduce some of the resistance to the pistons moving down on either the power stroke, or the intake stroke. According to Mike, the PCV valve will suck a vacuum into the crankcase if you seal up the breather. Hold on, don;t get upset till you hear the rest of it. It takes awhile for the vacuum to build up, and you must build in a small, controlable leak up top so you can adjust this vacuum to be no more than 6" of mercury so you do not suck your seals into the carnkcase thus creating massive oil leaks. It is a simple thing to put a check valve in the crank case breatherhose that allows pushing air out, but does now allow air in. I just realized as I am typing here, that this probably creates more of the vacuum than the PCV valve. So, here are the questions:

1. What problems do you foresee with this idea? Keep in mind he has done this many times, and I don;t want this to turn into an attack on MPGMike. I just want to explore the concept.

2. Can you imagine the hardware that would allow you to monitor the vacuum on the crankcase, and adjust it from the driver's seat? I know there are devices to control the boost on a turbo from the driver's seat by introducing a leak in the waste gate hose, or some such thing. I just cannot picture what kind of hardware could control this. Is there a valve that you could plug a vacuum hose into, that you could open and close to allow a controlled leak with a knob from inside the drivers compartment.
Mike talked about getting a needle valve from the line that controls the water flow to a refrigerator ice maker. I can't picture it, and I dont; know what I would be looking for.

3. And even cooler, is there a vacuum bleed down from one of the earlier emisions systems that would simply open after it hit 6" of mercury, and allowed a bleed to control the maximum vacuum inside the crank case. It seems as if there has got to be one of those small plastic canister devices that were about the size of a quarter that got inerted into the maze of vacuum lines in the early emmissions controls that were designed to hold vacuum up to a specified amount.

Mike says this is good for a 3 or 4 percent improvement in both performance and economy. It is small, but it is something, and tuning is mostly the accumulation of small things that ad up to a big thing. I know serious race cars run a vacuum pump to put a vacuum indside the crankcase, but their systems are elaborate, and expensive. This is the cheap way to get some improvement. I am hoping some good ideas will surface from this auspicious group of creative minds.

AFter I have played with this, I will report back, and let you know how it worked. Then it is on to the next idea, which I will share as well.



Sam

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Mike is a creative, out of the box thinker, and a good fabricator. The end goal that he is suggesting is similar to those crankcase vacuum pumps that drag racers use. I would have to think about using PCV to do this, but it may be possible.

For the record, I have used Mike's skills for a few projects, and I need his help on fabricating a fuel injection intake and fuel rail. So, Sam, as much as I love you brother, I am calling dibs on Mike's time.

Greg

PS. I get to DC fairly often. Can I stop by to see your Dart?

http://www.dragstuff.com/techarticles/vacuum-pumps.html

This may or may not help.

Greg

The theory of improved efficiency with a slight negative crankcase pressure is a sound one, but 3-4% sounds like an overly-optimistic estimate of the potential gain to be had, and the reduced airflow through the crankcase will necessarily mean poorer crankcase ventilation, which in turn means dirtier, wetter oil. I'm sure you could dial-in the crankcase vacuum by playing with different restrictor orifices installed in the breather's air inlet and a vacuum gauge at the dipstick tube, but even if you managed to achieve 6" max I really don't think you'd get a measurable gain in anything by going through all the work.

IMO, YMMV, SASE, etc.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

For a while I followed a forum for Geo Metro owners.
This forum is dedicated to getting the most MPG.
The man who runs it was consistently getting 61+ out of his Metro (IIRC).
{3 cylinder, 1.0 litre, 5 speed).

Anyhow, in all his modifications, the single largest improvement in MPG came when he disconnected his charging system. (Something like 4% improvement, I think).

Would this trick work on a Slant? I don't know. Of course, you then have to charge the battery at home, or rig up a switch to turn off the alternator only when you wanted.

-Mac

Sam,

I don't understand. Where do you plumb the breather or PCV lines to generate vacuum? Into the exhaust pipe?

They are already plumbed into the intake system to draw air out of the crankcase. You need a source of vacuum (effectively a pump of some sort) to draw the pressurized air out of the crankcase.

Lou

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Home of Slant6-powered fun machines since 1988

As I understand this, the breather cap in the top of the valve cover equalizes the crank pressure by allowing pulses both in and out of the crankcase. If you put a one way valve into the hose that is already plumbed from the breather to the air cleaner on most cars, and orient it so it will suck, but not blow then the vacuum will build as the pcv sucks on the crankcase. It is not alot of work. I have already purchased the check valve for a GM mid 80''s smog pump for $24. It has the same size hose fitting as the breather cap. The breather cap I am using is a GM cap. The GM cap is what fits the Aluminum rocker arm cover we purchased as a group 2 or 3 years ago. And this particular breater cap seals tight with no filter holes on the bottom like the stock Mopar one had.

The only challenge now is to control the vacuum in some way. That would be dead simple if I could find an emissions control part known to open and vent at 6" and above. If not, then I might want to monitor the crank case vacuum, and control it remotely from the cockpit. I do not invision this being alot of work, or cost. Thanks for your thoughts so far.

Greg, I will certainly honor your spot in Mike's line. I can tell you this, he is passionate about this stuff. I hope he finds a way to make alot of money, influences the auto world in a positive way, and has fun doing it.
I will report back on the success or lack of it of this little project. There are others I will share. Some are oriented strictly to EFI, so I will go to that section to make those posts. But that is off in the future. If I don;t do these one piece at a time, there is no way to know if they work, or what is doing what.
Sam

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The theory is sound, but then there is the practical application. For this to be feasable the engine must be in excellant condition. All the seals/gaskets/etc, must be able to, not only keep oil in, but air out. Then consider the condition of the rings/cylender walls. They must in good enough condidion, to be able to prevent more combustion gases from entering the crancase then the vacumm system can handle.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

If I read the description correctly, the vacuum is drawn through the existing PCV valve. The plumbing is to regulate the vacuum by sealing off the crankcase breather and installing some kind of regulating and monitoring system. I won't get into the benefits/drawbacks of such a system but the implementation seems to be fairly straight forward to me.
The easiest way would be to use the 3-hole valve cover and simply plug the breather hole. A nipple could be welded in to the valve cover and a tube routed into the cabin. The tube could then be connected with a tee connector to a vacuum gauge and a simple valve to adjust the bleed off to maintain a certain maximum vacuum level. The vacuum would, of course, vary with engine operating conditions. You could get fancy and use some kind of adjustable regulator but what I've described above would be quick and easy to implement for experimentation purposes. By using the 3-hole valve cover you can easily eliminate the crankcase breather cap, seal the valve cover and still have access to add oil to the crankcase.

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David Kight
'62 Valiant Signet, White
'98 Dodge Dakota
'06 Jeep Liberty

Growing older is unavoidable but growing up is strictly optional.

Good point Charlie. I think this engine is sound enough. I rebuilt it two years ago, and it has few miles on it. I does not seem to leave any spots on the garage floor. But that thought does concern me as well. It does seem as if this application would have to be limited to a solid, tight engine.

Sam

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A turbo engine isn't going to generate very much vacuum through the PCV system on its own (I presume you've plumbed the hose between the air filter and the turbo). How about using a smog pump plumbed into the PCV system to give it a bit more suction? That way you would only need a small amount of restriction on the air coming in and could get better airflow through the crankcase.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

Thanks Matt, and Charlie, this is the type of rumination I was hoping would surface; sort of an ongoing brainstorming session to explore the pros and cons, so no hidden "gotchas" surface later.

If you use a smog pump, you have lost power through the action of driving the pump. That might be a net loss. As I see it, this would be mostly cruise economy. When you talk about the hose between the air filter and the turbo, are you meaning the main induction air inlet to the turbo? If you mean something else, I might be missing an essential part of the system.

Sam

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Yes, I just meant the turbo inlet plumbing. It would have to be upstream of the compressor for the PCV system to work full-time.

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"Mad Scientist" Matt Cramer
'66 Dart - turbocharged 225
My blog - Mad Scientist Matt's Lair

The PCV is between the valve cover and the throttle body,so I think it is outside the influence of the turbo. Since it is a check valve, does it not close off when under pressure from the TB. Thinking things like this through are bound to keep your mind young. They say working a cross word puzzle a day keeps your mind young. I think this car stuff does that as well.


Sam

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Too bad the "Breather" thread from .com is lost. There actually was a good bit of discussion about the effects of vacuum on a crankcase. IIRC, general thought was that the most you could pull would be 2-3".

In the real world, we use vacuum pumps on race motors, and you do not see an appreciable gain in horsepower until you get to 10-12" of vacuum. The engine must be sealed very well to hold it too, no dipstick tube or anything.

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Official Cookie and Mater Tormentor.