Yes -oil return tube is clear-1st thing I checked

Thanks, Chuck

Hello Chuck,

I had a very similar situation with my 57 Fairlane (292).  After a complete engine rebuild, I was advised by the engine shop to run the engine at 1800 RPM for 20 minutes to "run in" the cam (something that is common after an engine rebuild with new camshaft).  After shutting down the engine there was a large puddle under the draft tube.  I had installed a new filter when re-installing the engine and the gasket to the block was new and tight.  I had quite a bit of oil spray when driving the car and the source appeared to be the draft tube as well.

I decided to try a modification to the draft tube cannister (pictures attached) that worked very well right from the start (the engine was rebuilt in early 2009 and now has around 5,000 miles on it).  I replaced the filter with a section of 2" PVC pipe (the filter is 2.25" outside diameter and the 2" PVC is 2.375" so it seemed to fit within the cover okay).  I made the pipe length 1.875" (same as the filter) and cut a notch out of the front upper portion of the pipe to allow for air flow.  The PVC pipe was glued in place using JB Weld and it acts as a "dam" to block oil from flowing into the draft tube before it can flow back into the block through the return tube.  My reasoning for eliminating the filter is that the air flow is always from the engine out to the draft tube, so it is doubtful that that any dirt could enter the engine from the draft tube.  I also never drive on dusty roads, so that may be a consideration if you do.  You could "patch in" a portion of filter in the notch of the pipe if concerned.

In any case, the modification has worked very well.  There was no longer any expulsion of oil from the tube while driving or accumulation after parking the car.  I'm sure there are other fixes, including adding a PCV valve and directing the flow through the carburetor, but I found this to work well for me.

Regards,

Dave

   

Blow by is perfectly normal on any engine including brand new ones today.  That is why all engines went from a vent to a pcv system.  That way any blow by gases and oil film will just return through the engine.  If you ever notice the cummins engine on like 99-06 Dodge.  EPA did not regulate what they had to do with there crank case gases so dodge ran a tube down the side of the engine which drip oil on the ground and make a mess all over the truck.  Even if you have some oil dropps and if the engine is new it is perfectly normal.  If you want to eliminate it what I did was put a fitting in my exhaust pipe that is angled so the exhaust gases will actually create a vacumm on the breather pipe and help pull a slight vacuum on the crank case which will actually help your engine perform too.  You can buy everything through jegs.  The fitting and there is check valve you install so exhaust won't go back into your crank.

Vacuum systems that use the exhaust flow as the flow driver are typically non-effective in daily driver situations when hooked up to an exhaust system that has mufflers or long small diameter pipes.  This is simply due to any back pressure present reducing the negative air pressure flow across the installed nozzle and subsequently prevents a vacuum or negative pressure from being generated.  These types of vacuum evacuation systems are ideally suited on open headers that have no mufflers and as a result, these systems do work well on the racing applications.  Here’s a picture of the evacuation system on my roadster.

 

Lorena, Texas (South of Waco)

Welcome to the site.  You might double check the face of the draft tube where it bolts to the block and insure it’s flat.  These are easily deformed and the gasket simply doesn’t do its job in sealing against a surface that’s not quite flat.

Lorena, Texas (South of Waco)

Am I missing something? Since race cars usually travel at a high rate of speed, would an exhaust rigged evacuation system (aside for brief idling periods) be any better than a T-Bird style valley cover draft tube that never leaks? Some racetracks require mufflers, and a charge mixture diluted with blow-by gasses would have to burn leaner and thus contain less energy/HP potential than pure gasoline.

6 VOLTS/POS. GRD. NW INDIANA

Assuming the exhaust pulses are approaching the speed of sound, then an undercar road pipe would need to see ~777 mph to get an equivalent speed effect that generates the same negative air pressure as does an exhaust system driven evacuation system.  That’s the simple explanation.  Road draft tubes by design were not to make a negative pressure within the engine but instead promote air movement through the engine.

For what it’s worth, the exhaust driven system on my roadster is working well at 2500 rpms and just gets better as the rpms go up.  Many high end race cars (and especially those that use mufflers) incorporate either electric or belt driven vacuum pumps to maintain a negative pressure within the crankcase in lieu of using an exhaust driven evacuation system.  I’ve seen as much as 30HP on engines that use a belt driven vacuum pump versus no pump at all so there’s definitely some power to be found in running a negative pressure on the crankcase regardless of the method employed.

The exhaust driven evacuation systems are not tied to the intake tracts but instead to the crankcase usually by way of the valve covers.  A check valve at the header keeps any unwanted exhaust pressure from making its way back to the crankcase in the event backpressure does take place.  These types of evacuation systems are not to be confused with positive crankcase ventilation systems which serve a different purpose.

Lorena, Texas (South of Waco)

I guess I am confused. Can you elaborate on the differences between PCV, which uses intake vacuum to clear the crankcase, and the systems which use an even higher vacuum to clear the crankcase?

Jim - Erie Colorado, 1957 Country Sedan

A PCV valve is simply a controlled vacuum leak which requires an adjustment to the air fuel ratio in which to compensate.  PCV systems utilize the engine manifold vacuum to pull air from the crankcase whereas auxillary pumps (electric or belt driven) or exhaust driven systems do not require engine vacuum in which to operate.  But the purposes for each do vary.

 

PCV valve systems are specifically for removing moisture or excess pressure from the crankcase which would be an environmental concern if not reburned through the engine.  PCV systems are typically a flow through design that do not pull a vacuum on a crankcase but can remove enough excess pressure that any existing oil leakage can be significantly reduced.  If a PCV valve is used on a sealed system, then a reduction in crankcase pressure will be realized but its ability to actually remove any moisture or condensate from a warming up engine will be compromised.  It’s that flow through design that actually allows contaminates to be moved to the PCV valve where it can be reburned through the engine.

 

Auxillary driven pumps are for removing air itself from the crankcase and are realized more for their performance gains than for environmental purposes.  This is because these air pumps are designed to remove air on a sealed system rather than simply allowing air to flow through the engine.  Removing air from the crankcase frees up horsepower simply due to the pistons not having to work as hard in moving it around.  Air has mass and as a result it takes a given amount of power to move it around.  These same auxillary systems can also improve compression ring seal but there are some detriments to having too much negative pressure in the crankcase.  First is a reduction in oil pressure and secondary is some starving of oil in top end parts such as around the wrist pins.  For this reason, many auxillary engine vacuum systems will have an adjustable vacuum break to limit the amount of negative pressure that can be generated within a crankcase.

Lorena, Texas (South of Waco)

Boy, you learn something new everyday. Had no idea of the potential HP gains realized through neg. crankcase pressure. I had always assumed the exhaust-driven evac. system's purpose was akin to typical PCV benefits (drawing out blow-by gasses at idle, and relieving some pressure at high revs). If that system is supposed to be closed in order to maintain neg. pressure, then modern exhaust or pump-driven evac. motors likely don't have all the extra valve cover breathers we are used to seeing in 60s era race engines that bled off the excess pressure created at very high RPMs?

6 VOLTS/POS. GRD. NW INDIANA