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Advice for fellow TR owners from Tom Shea Racing
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Crankcase Pressure Evacuation
Our engines suffer the plight of all small engines making big power. The power to engine size ratio determines the cylinder pressure. This pressure can be substantial in an engine making even ½ horse per cubic inch. Some of our engines are at 2 to 3 horsepower per cube.
The tremendous pressure required to generate that kind of power is not totally contained by the piston rings. That would be physically impossible. The gasses that are forced past the rings by this pressure ends up in the crankcase. This gas has to be vented, since the crankcase is not designed to be pressurized.
The following modifications do not comply with the emission controls designed and built into our cars from the factory. The legality of these mods for street use should be researched prior to use. Off road or track use is quite common.
The most common way of dealing with this is to use small K&N style filters on the valve covers. We also have a PCV valve in the intake manifold. This is designed to seat and seal under boost. This valve is closed under boost if operating correctly. Unfortunately, some boost can get past this valve and contribute to crankcase pressurization.
Some engines vent this PCV directly to atmosphere, to address this issue. This modification will also eliminate the function of this valve when there is vacuum present. Those non boost times, with the engine running, would have had sufficient vacuum to draw a slight flow into the intake. This is the normal, non-modified function of this valve.
If this PCV valve is modified to vent to atmosphere, the vacuum source will have to be blocked off. This can have a slight effect on the fumes at the valve covers. Since there is no longer a slight draw from the manifold vacuum, there can be a small amount of vapors escaping from the crankcase at the valve cover vents.
The valve cover vents will collect the small atomized particles of oil in the fumes and then drip it onto the valve covers. The more boost / power / cylinder pressure, the more oil on the valve covers. This oil will eventually end up dripping down off the back of the cover and onto the various other parts of the car including the exhaust pipes.
Depending on the particular application, there can be a lot of oil making a pretty big mess. This is not “Going Fast With CLASS!”
I have been meaning to address this issue for years, and in the meantime have been living with trying to keep the oil wiped up as well as I could. I had a lot of oil on my undercarriage and dripping on the floor in my parking spot.
This is not an uncommon problem. Those that deny it are not fooling anyone. My engine is very tight and fresh. This is not an engine problem, just an oil control issue.
There is more than one way to address any issue. The simplest ways are usually the best. The simple way for this would be a non powered collection system with a catch can. There was a set-up like that on my engine when I bought it from a racer. I never used it, but I’m sure it would work to some extent.
At this point I should credit Walt Judy, for some of the original tech for this. I talked to him at the GS Nats, many years ago. He had a very inexpensive setup on his car back then. He rigged it up from a GM vacuum assist pump for power brakes. He found the parts in a salvage yard. His system was very cost effective and functional.
When I finally got around to attempting the set-up on my car I called Nick Micale at Arizona GN. He was using some of the components that I had in mind. He was very helpful and took the time to discuss it with me. My system is not identical to his but very similar except for the Hobbs switch control I’m using instead of his constant on.
Components are valve cover oil fill caps with hose nipples, ¾ in rubber hose, Various Tees and fittings, an inline oil separator, a GM AIR pump ( for a late model f body), and an after the pump final vent reservoir. The AIR pump is controlled by a boost activated switch (Hobbs). This causes the pump to run only when the engine is under boost.
The pump fits nicely in the left front inner fender pocket. This is the area originally used for the charcoal canister. The Rubber hose routes and fits well around the back of the engine from both valve covers and then Tees together to route up to the left front of the engine compartment. This is where it goes through the inline oil separator and then into the pump. The hose out of the pump goes through the left front access hole to behind the headlight. The final vent reservoir is located there. These reservoirs should be placed for easy access to service. They will need to be checked and drained occasionally.
I opened the pump housing and removed the inner foam packing for better air flow, and to avoid oil saturation.
The Hobbs switch can be placed anywhere in the boost / vac system, just keep the check valves in mind. I used a 30 amp automotive relay from Radio Shak from the back of the alternator with a 30 amp fuse for power. I used the inner fender bolts for grounds.
The components can be found in Summit or Jegs, except for the AIR pump. The cost of the AIR pump new from GM will range somewhere between 1 and 2 hundred dollars. The 2 reservoirs will be less than 100 each. The ¾ in hose and fittings can be inexpensive, since they are not subject to a great deal of stress. All total The cost of the components should come to between 3 and 4 hundred dollars.
I do not have any actual real world testing time on this system since it’s the middle of the winter off season here in Minnesota. I’ll assume that it will do as expected come next season. If there are any further issues, I’ll post them. If not, then after some use time next spring 2008, I may have enough testing done to form an opinion.
The only question I have right now is if there is a need to run the pump full time instead of under boost only.
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