Carnkcase Evacuation

[mwvdub]

I have a 1979 F100 race truck with a 514. I had new headers built for it over the winter with evac tubes in the collector. I looked inside the header and the tube is installed about halfway in the collector, about 2" installed depth, and not cut at a very good angle. I pulled the valve cover breather and it seems the tube is actually blowing back into the valve cover instead of sucking pressure and running it out the exhaust. I replaced the check valves but still not helping much. Should I shorten the tubes and cut them at a 45 degree angle to the exhaust flow?

[Bear River]

I am very confused. Aren't you supposed to let the engine vacuum evacuate the crankcase?

[mwvdub]

I am using this kit from moroso... http://www.summitracing.com/parts/MOR-25900/. It is based off Bernoulli's principle. Engine exhaust flow across the evac tube cross section should draw the pressure from the valve cover through the hose and out the exhaust along with any blowby, etc. The problem I have is the cross section is cut at the wrong angle to the exhaust flow and the force of the exhaust is blowing from the collector back up into the valve cover.

[dkf]

If it were me I would just run a standard breather on each valve cover and cut the tubes out of the collectors and weld the holes shut.

[mwvdub]

Originally Posted by dkf

If it were me I would just run a standard breather on each valve cover and cut the tubes out of the collectors and weld the holes shut.

I dont like it blowing oily mist all over my $10K engine.

[Bear River]

Run the breather to the intake somewhere. The best thing to do with waste oil fumes is to burn it and turn it into power. Its cleaner and is in my opinion the best approach. The bernoulli principle is nice, but realize that an exhaust system does contain pressure waves, and under the right conditions will create a good venturi, but the volume and pressures in an exhaust system is always changing, and may not always form a good venturi under all conditions. To use it requires a low of knowledge and that the system is tuned to your conditions. The fact that you are having any problems tells me this system is not engineered to the necessary level to do that.

[75F350]

You mentioned that the 'nipple' was protruding through the collector? The depth is causing more problems than it is obviously helping.. When I set mine up (557) I had several trial and errors in an attempt to reduce pressure build up. Things changed slightly when I installed mufflers. In your case, if you have the tubes penetrating too far, this would explain you reverse pressure. This is counterproductive, and can easilly be fixed.
During my trial and error, I placed a bag over the end of the hose, and watched what the bag would do. If the bag inflated (regular gorcery bag wrapped with electrical tape, real high tech) then I know I was getting reverse pressure, and I needed to move the instertion tube. Once the bag would deflate and suck into the tube, I knew I had it close.
Mine currently sit at an angle but flush with the inside of the collector so that the insertion tube itself does not disturb the flow within the collector and disturb the scavenging affect. Turn the air around here, and you might as well be running cheap headers.
Keep in mind that not only are the tubes cut at angles, but they get welded in at an angle too. I believe that the hole was 7/8" for mine, and I tig welded them.
There is no science to this, only that you must achieve the highest amount of vacuum while the exhaust flow is at its greatest. I pull almost 4 inches all of the time.(once it is close, you can put a gauge on it) Largest problem was when I was stabbing the throttle under severe loads. Mud and the street apply very different loads on the engine, but the air flow past the pitot tube are very similar, so you should have no problems, once you get the angle and penetration correct.
Again, you do not want to just stick the tube into the collector and hope to get lucky.

This is considered "free" horsepower, as it requires no belt to turn a pump, nor does it require anything electrical that will draw from the alternator.
Unfortunatley, get it wrong, and you fill the crankcase up with pressure and you go backwards. You rob power, and contaminate your oil.
This is worth a few thousanths if not more.
Some have gone the electric pump method, but your kit is probably suitable:

[mwvdub]

Thank You 75F350. I think the full exhaust is causing the exhaust gas to move to slow to cause low pressure across the tube plus the tube is cut an odd angle to the flow. I am going to take the headers off on thursday and see if I can cut the nipples better. If not I found a thread on 460ford about a factory ford pump that people have had luck with.