Oil Catch Cans - Fact Or Fiction

Luke Munnell Stephen Rhim & Debunking Tuning Myths
So, here's a product we never thought of as a power adder: an oil catch can. Traditionally added to keep cylinder heads and intake tracts vented and clean, rather than to increase power, this month's theory posits that replacing a breather filter with a properly engineered catch can will bring power gains, as well.

Will Oil Catch Cans Yield More Power?
Here's Why:
Catch cans fit between a port in an engine's valve cover and its intake and use the vacuum from an engine's intake to draw blow-by contaminants (oil, fuel, and exhaust gas that seep past the valve seals during combustion) out of the cylinder head and into a reservoir where they can be manually disposed of. In doing so, they also create low pressure within the head, allowing components to move more freely, decreasing parasitic loss. In many OEM applications, a simple vacuum hose is placed between the valve cover and the intake, which alleviates excess cylinder-head pressure and draws contaminates out of the cylinder head, but at the cost of re-circulating them throughout the intake tract; soiling intake manifolds, fuel injectors, valves, and decreasing intercooling performance of force-induced cars. Even more detrimental is when those cute little breather filters are used instead, that neither vent excess blow-by pressure as much as a vacuum-driven alternative, nor stint the build-up of contaminants in the cylinder head-doubly robbing power.

Now, we know catch cans trap contaminates, but to test whether or not installing a catch can will increase power, we thought it logical to install one of the best ones we could find-our Circuit Sports unit-on one of the dirtiest engines we could find-the SR20DET in Carter's 240SX-and compare its power output versus an off-the-shelf breather filter. To ensure testing accuracy, we put on a designated amount of highway miles with each arrangement before visiting the rollers of XS Engineering's Dyno to test for power changes with multiple runs at each stage. Here's what we saw:

Test 1
Catch Can, Circuit Sports: 244.3 WHP AVG

Test 2
Breather Filter, Autozone: 242.8 WHP AVG

The Verdict:
Not only did the catch can make power; we could actually see how it worked. A noticeable amount of blow-by sludge accumulated in the tank after extensive highway driving and dyno testing, and compared to the breather filter, there was no question. Power numbers were the lowest of the day, as blow-by pressure had a significantly harder time exiting the head than when sucked out by the catch can. The short end of it is: Catch cans work. They keep engines clean and vent power-robbing pressure from their cylinder heads. The more moving parts make up your engine's cylinder head(s), the higher cylinder pressures increase-or the more your engine suffers from blow-by, the more a catch can will help.