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Should my Webers suck on my crankcase?

FM Former Member
Which is better, a standard breather box with both valve covers and the oil fill tube vented to the atmosphere through a breather box? Or to have the valve covers and oil fill tube plumbed directly into the top of my air cleaner? On the latter, a vacuum sucking the oil back into the engine seem desireable, but the vaporous residue gets to collect in my Webers. On the other hand my Webers remain virgin, but the crankcase pressure vents only to the atmosphere. Which trade off do you feel is the better?

How about a sealed breather box, connected to the air cleaner but the vacuum line is protected by a good oil vapor filtering media. Thanks for any thoughts.
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FM Former Member
Which is better, a standard breather box with both valve covers and the oil fill tube vented to the atmosphere through a breather box? Or to have the valve covers and oil fill tube plumbed directly into the top of my air cleaner? On the latter, a vacuum sucking the oil back into the engine seem desireable, but the vaporous residue gets to collect in my Webers. On the other hand my Webers remain virgin, but the crankcase pressure vents only to the atmosphere. Which trade off do you feel is the better?

How about a sealed breather box, connected to the air cleaner but the vacuum line is protected by a good oil vapor filtering media. Thanks for any thoughts.
FM Former Member
Vent both valve covers and the oil filler casting to the bottom of an external, baffled breather box, then vent the top outlet(s) of the breather box (vapor) to both carburetor air cleaners. You can keep the bottom "road tube" stock or plug it when you use the breather box; in my opinion plugged would be better (keep more junk out of the engine).
(Message Edited 6/26/2003 4:06:47 PM)
FM Former Member
Good thing you didn't vent to the header - you need to know where and how much of a pressure drop exists, and it can suck oil out of the engine. VW drag racers that do that usually suck a fair amount of oil out during a 1/4 mile run.

Don't bother with a baffled vacuum pump setup on the sump, either, as it will only add a few BHP at much higher RPM.
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