DIY Crankcase Vacuum Project
Beginning back around 2008, I started down the path crankcase vacuum for my street/strip car. I had just built an engine with a set of low-tension rings designed for class racers, and it went thru a qt of 5w-20 Mobil1 in less than 100mi.
My first attempt was to add an electric vacuum pump that was commonly used in OEM emissions systems, bought this one from Amazon...
My first attempt was to add an electric vacuum pump that was commonly used in OEM emissions systems, bought this one from Amazon...
I made a bracket to mount the electric pump (Delco 215-425) under my RX-7's dash, connecting it to the engine with a 3/4"id rubber hose. I also put a 3/4"id hose on the "out" port of the pump to take the crankcase smells out/under the car. The pump made little noise inside the car, as the hose carried most of the "vacuum cleaner" noises outside the car...
For the valve cover connections I made some quick-connect o-ring fittings from Delrin, they are a snug fit into the valvecover pipes. Makes for easy valvecover removal...
I also made the separator can out of hardware store pvc pipe, then turned the outside to make it look better. It only weighs ounces...
I ran this setup for a season, no problems at all. I did draw 4"Hg on 12v with the engine running, but i installed a dropping resistor so that the pump runs on reduced voltage until my nitrous came on. Completely eliminated my oil leaks. I thought about removing the separator tank all together and replacing it with a simple "Y", as the tank and hoses show very little evidence of pulling oil. The valvecovers do not have any baffles, but i think the reason I wasn't seeing more than a few drops of oil is because i'm turned the pump on before the engine starts.
Some say this type of setup won't gain you any power, but there's no denying that there is power (and mileage) in a low-drag ring pack. If it allows you to use lower tension rings, the engine will be more efficient. My street driven old-school SBC had 1.2mm 1st and 2nd rings and 12lb oil rings, went even lower on the oil rings next time around.
The difference between a shortblock that takes 12ft/lbs to turn over vs one that takes 35ft/lbs? at 7500rpm, it's about 33hp. Cruising down the hiway at 2500rpms, the difference is right at 11hp. That 11hp difference is additional friction wearing out your bores and wasted fuel, just adding to the load that your cooling system has to deal with.
The difference between a shortblock that takes 12ft/lbs to turn over vs one that takes 35ft/lbs? at 7500rpm, it's about 33hp. Cruising down the hiway at 2500rpms, the difference is right at 11hp. That 11hp difference is additional friction wearing out your bores and wasted fuel, just adding to the load that your cooling system has to deal with.
Making the DIY Crankcase Vacuum System Better
Eventually I started to think about how I could make the system better. The 12v electric pump put a constant load on my alternator, so I began to wonder if adding a pcv valve would allow me to turn off the electric pump while casually driving. First thing I did was to add a screw to the elbow of a common sbc pcv valve, which allowed me to adjust the minimum flow rate of the valve. Then I made a hole in the top of the catch can to install the valve. Also had to add a large header style check valve to the end of the electric pump's discharge hose, didn't want the pcv valve to draw air thru the pump when it was not running...
Adding the pcv valve proved to be a huge improvement, as I was able to pull 15"Hg in the crankcase @ 2500rpm down the highway without even turning the electric pump on. At this point I only turned the electric pump on when I was getting ready to make a WOT pass. Much less wear/tear on the electric pump, plenty of crankcase vacuum, didn't think it could get much better...
...until one day I forgot to turn the electric pump on! Now you might think crankcase vacuum would instantly drop to zero at WOT with a pcv valve as the vacuum source. Turns out in reality, crankcase vacuum drops slowly @ WOT as blow-by fills the vacuum. In my case the pcv valve doesn't have to keep up with WOT blow-by, only stay ahead of it for 10sec or less. I've been running this system for several years now, never seen a situation where the crankcase ran out of vacuum with the engine WOT. Without crankcase vacuum, these low-tension rings went thru a qt of oil in ~100mi. With crankcase vacuum, might have to add a qt all summer.
...until one day I forgot to turn the electric pump on! Now you might think crankcase vacuum would instantly drop to zero at WOT with a pcv valve as the vacuum source. Turns out in reality, crankcase vacuum drops slowly @ WOT as blow-by fills the vacuum. In my case the pcv valve doesn't have to keep up with WOT blow-by, only stay ahead of it for 10sec or less. I've been running this system for several years now, never seen a situation where the crankcase ran out of vacuum with the engine WOT. Without crankcase vacuum, these low-tension rings went thru a qt of oil in ~100mi. With crankcase vacuum, might have to add a qt all summer.
Current Evolution of the PCV Valve Based EVAC System
Next I decided to completely eliminate the electric pump and most of the plumbing, and replace it with cross-over breathers with internal check-valves. I used common K&N style breathers, and made ball seats out of Delrin that pressed inside the breather mounting tubes. The check balls were initially 1" dia nylon bearing balls as shown in the picture below, but I have since switched to 1" dia Viton rubber balls...
As you can see, I also moved the pcv valve to in-between the breather tubes. The 1" dia rubber check balls inside the breathers serve to allow the pcv valve to draw a vacuum inside the crankcase. If something goes wrong and the pcv valve for some reason can't keep up, the breathers open up to vent any pressure. This system currently pulls 17-18"Hg @ 2300rpm down the highway, might have to add a qt of oil all summer :)