Crankcase Evacuation: When It's Cool to Suck

[lafinrat]

Blow-by is a term used to describe the amount of positive pressure (above atmospheric) that passes the piston rings and makes its way into the crankcase. The amount of blow-by is based on several factors, and all engines have blow-by. High performance engines have more blow-by than stock or lower-powered engines due to bigger cylinders, higher pressures, and loose clearances needed for everything to expand with heat. Some of the negatives effects of blow-by are external oil leaks, loss of power due to pressure on the bottom of the pistons, and in extreme cases ring flutter and poor ring seal at high revs. Advantages to reducing crankcase pressure include: more power, better ring seal, and better oil control.

There are several ways to combat positive crankcase pressure, and there are some drawbacks to each system. There are disadvantages to all methods and every engine will respond differently to each type of system. For now, we'll examine 3 different approaches at making your crankcase 'suck'.

For all 3 systems, the crankcase must be completely sealed. Performance of any given kit can be measured by installing a vacuum gauge somewhere on the engine. Some folks use a modified fuel pump mounting plate or blockoff with a nipple to temporarily measure crankcase pressure. Ideally a wet sump motor should have 0-5 inches of vacuum at WOT. Dry sump motors can have up to 13-15 in. Too much vacuum in a wet sump system will cavitate the sump-mounted oil pump and cause more harm than good.

1. Exhaust-driven 'pan-evac' kits
Your car will be loud. These kits say 'no mufflers' and 'not for street use' on the package. Basically they take the negative exhaust pulse and pull air from the crankcase into the exhaust header. A smog pump diverter valve (one-way valve) is used atop a welded header bung to keep the positive exhaust pulses from back-feeding into the crankcase. Mopar-style breathers on the valve covers hook to the diverter valves on the header collectors. This setup has been around for years and mufflers CAN be used provided there is no backpressure, unfortunately these types of mufflers don't provide much 'muffling'.
pros: cheap, easy, effective
cons: not for street*, i have however used this system for years with various mufflers, some of them worked some did not, the ones that work are LOUD

2. OEM smog pump
This system uses an OEM smog pump (usually a GM-style) with the inlet (suction) side of the pump hooked to one valve cover via a hose and bung. An adjustable vacuum regulator is used on the other cover to regulate pressure in the crankcase. The outlet (vent) side of the pump is hooked to a vented collection can mounted somewhere in the engine bay.
pros: cheap, effective
cons: These pumps are designed for dry air, NOT oil. There will be oil vapor in the crankcase fumes. It has been reported that these vapors will eventually damage the smog pump and constantly make a mess. Its suggested that the crankcase pressure be monitored constantly to check for pump failure--one more gauge to watch. Also, it has been said that these pumps are not capable of keeping up with high power applications where blow-by is considerable. I tried one of these pumps and it would not even pull the case down to atmospheric on my bbc.

3. Purpose-built vacuum pump (e.g. Moroso 3/4 vane, Aerospace, Arizona Speed)
This system works like the above minus the OEM smog pump and add a higher capacity purpose-built vacuum pump.
pros: best you can get, not effected by exhaust back pressure
cons: expensive
Watch out for too much vacuum with these systems and be sure to use the correct rear main and front seals designed for vacuum pump usage.

[12second5.0]

I'd like to add that a few auto manufacturers use an electric smog pump.I believe Cadillac is one.You can probably pick these up for next to nothing at a salvage yard and use this.....

[SpdBoss]

thats some good info right there. thanks guys