Exhaust Evacuation

[SourceLee]

Is anyone running an exhaust crankcase evacuation system? If so, what setup are you using? Moroso, Milidon, Allstar and others make different versions of the system. For clarification purposes, an exhaust evacuation is different than a vacuum pump or intake manifold type. The primary functions of the vacuum pump and intake manifold type can be argued until the cows come home. However the exhaust evacuation system (ECES for short) to the greater extent is fairly straight forward. I first read about ECES back in the 80's. The purpose of the type I'm referring to is to pull fresh air through the crankcase. It does so by using a venturi located in the exhaust system. What's nice about an ECES is they have no measurable negative effect to the performance of the engine. From my understanding their purpose is to remove caustic gases from the crankcase. The undesirable gasses can be detrimental to engine components. More importantly these gases will degrade engine oil. The life and blood of most engines. The purpose of this specific venturi is not to pull a hard vacuum. More so to facilitate air flow. The crankcase is really never under any sizable vacuum with an ECES. Here's an oversimplified setup. There're other components but you'll get the idea. Venturi tube in the exhaust system is connected to one valve cover bank via a tube. Air filter located on the other valve cover bank. Venturi located in exhaust system pulls crankcase gases from one bank. On the opposite bank fresh air enters through the valve cover air filter. What's for dinner? Comments, arguments, experiences etc. are all welcome.

[Bob Cowan]

I looked in to that a while back. At high rpm's, they work great. At lower rpm's, they'll fill the crank case with exhaust gasses. That's a bad thing. It's strictly a racing part, not suitable for a street car.

[NAZ]

While I've never tried them with mufflers I do know that they are not recommended for use with mufflers due to the back pressure. They're very common with drag racers but as Bob said, they work good at high RPM and not so much at lower RPM. I don't run them on my Hot Rod as I sometimes drive it on the street with mufflers. I run simple valve cover vents, two per side, that work fine on a 406 up to 8,000 RPM. It allows the detrimental by-products of combustion to discharge, which it seems you're most interested in. If you expect any performance improvement by running a exhaust siphon system you'll be disappointed.

Now the main benefit of running a vacuum pump for crankcase vent is it allows you to run rings with less tension. It increases the delta P across the rings and improves the seal without heavy tension. The frictional losses from your rings are significant, up to ~40%. Now if you set up the engine to be under negative pressure it will reduce windage losses at high RPM so you can see a HP bump at high RPM. And if you run a dry sump you get the benefit of crankcase ventilation without an add-on vacuum pump.