Evac Purpose

[7racecar7]

Hello,

Ive read a few of the post on an evac setup from the valve covers to the exhaust using a kit, can someone explain the main purpose of running an evac setup on a oval track race engine?

[ZIGGY]

Coupled with suitable piston rings, evac allows power gain from better sealing, reduced friction & charge contamination, and all around improved oil control.
If you asking specifically about header to vc systems on a ct car and not pump evac, IME hard to gain much but you take what you can get if you're real serious. I believe 5-6hg. from a header system is doable but 3 negative more likely for most.
Check valve life can be a problem especially if you use cheap crap. Pump is a better way to go. Can be homemade.

[Cedarmachine]

A real big bonus of having some sort of evac on a circle track engine is the reduction of condensation moisture collecting in the engine. I have built engines for guys and installed evacs and they immediately report back that they don't have the white milk foam in the valve covers that thay are used to seeing when they do adjustments.

This has to help with ring and bearing longevity. Remember also, surface rust on valve springs can lead to stress fractures and failure. L-19 rod bolts don't like the moisture much either...

Evacs are a win-win.

[#84Dave]

Remembering also that piston/rod pin clearance must also be considered when running a vacuum inside the engine. A vacuum tends to 'dry' the pins of oil and galling can occur. I've had total success running .0015" pin clearance with a vacuum in the engine. -Dave-

[PackardV8]

Ive read a few of the post on an evac setup from the valve covers to the exhaust using a kit, can someone explain the main purpose of running an evac setup on a oval track race engine?

Yes, if the plumbing and valve is right, if the header is tuned right and if the the outlet is positioned properly in the header, enough negative pressure can occur to suck a lot of moisture/fumes out of the engine. However, we've all seen some attempts which had none of the above. These days, header systems are pretty much po'boy and it's almost as easy to fab and run a pump system.

Pump is a better way to go. Can be homemade.

A search will find some examples fabbed from old smog pumps.

A vacuum tends to 'dry' the pins of oil and galling can occur.

Pump evac systems are a classic case of if some's good, more's better and too much will fry the engine.

jack vines