Just a general technical question.

If WRX's stock oil capacity is ~ 5 quarts, what is the advantage of having 7 quarts in there using aftermarket parts.

For example an oil cooler I have adds 0.9quarts and the oil pan adds another 1quart.

Please teach me...

 

Well, having an increased volume of oil in the engine is never a bad thing. More oil means the internals will be better lubricated and reduce wear on parts. Not only that, it will also reduce overall oil temps. I was thinking about gettin an ARC oil pan for my car to increase the oil capacity by 1-2 quarts as well.

Now, do I get an avatar Alex?

Edit: Also by using a smaller oil filter you can effectively increase the oil pressure as well. Which helps in oil circulation.

 

Oil capacity is good. Additional capacity should not be gained by overfilling the stock crankcase oil pan. This would move the oil level in the sump closer to the rotating mass of the crankshaft, piston, and rod assemblies, creating additional windage losses in the engine.

At high RPM, oil does not drop straight back into the oil pan has a tendency to be suspended around the crankshaft like a rope, consuming power that could be used to drive the wheels. In high-horsepower race cars, the oil level will be kept as far from the rotating assembly as is practical, but in the real world this is dictated by the chassis clearance.

Some race cars gain additional oil capacity by enlarging the oil pan with side kickouts but again this is limited by both the chassis and other engine components such as the exhaust manifolds. Also, oil slosh may be a problem if the pan is not designed correctly. The oil pump pickup should never be allowed to be uncovered to suck air. Engine builders have experimented with all sorts of screens, baffles, crank scrapers, windage trays, and swinging oil pump pickups in order to provide oil control in the sump.

The ultimate setup for a road race or drag car is a dry sump system, with scavenge pumps that draw all of the oil out of the oil pan, often resulting in measurable power gains when the oil can be kept from the rotating assembly. A dry sump allows greater oil capacity because it uses a separate reservoir mounted in the engine compartment. The oil pan itself can be shallower, allowing the race car engine to be mounted even lower in the chassis for a better handling vehicle. Dry sump systems are very complicated and if it isn't optimized for a particular engine, it may actually cause a power loss if the oil isn't being scavenged correctly. Some engine builders go so far as to install sight gauges in a dry sump pan to watch the oil level while the engine is run on a dyno. A well-designed dry sump system will leave much less than one quart of oil in the engine (depends on engine design, too) at redline without cavitation (drawing air), something a wet sump system cannot achieve. This can get tricky fast because the scavenge pumps work so well that negative crankcase pressure (vacuum) is created, which also aids piston ring sealing at high RPM. The problem with this is that conventional engine seals are designed to maintain a seal against leaks from the pressure contained within the crankcase. When there is a vacuum inside of the crankcase, it sucks in air and grit and breaks down the seals.

Oil should not be overcooled, either. Oil should be hot enough to vaporize moisture. Full power should be avoided until the oil temperature has stabilized. This operating temperature takes longer than the engine coolant to come up to temperature. Cold oil results in higher oil pressure, which in turn requires more horsepower to drive the oil pump.

I believe that the oil filter should be larger than stock if there's sufficient clearance or a remote oil filter mount is used in conjunction with an oil cooler. Larger filter means less pressure drop because there is more surface area of the filter media. Use recommended lines for external add-ons because too small of an inside diameter will cause a pressure drop if the lines are long.

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0==WW==0
"…axles of evil…" - george w. bush

 

Wow.

Interesting.

I am running Trust Oil Cooler that adds 1 quart and ARC oil pan which adds another quart. Just curious to know how good that really is.

Nice info Alan. Thanks! Thanks to you too, Lurk.

 

isnt wrx 4.7 hehe not too technical

 

yeah, you are correct.