Scott's 2 pence worth on engine breathers

Breathe and let breathe

Date: Tue, 5 Aug 1997 10:33:57 +0100
From: Scott A. Beavis
To: mini-list@autox.team.net
Subject: *Mayonnaise on toast
There was some discussion lately about breathers and whether you really need them. Here's my twopence worth:

For:

  • Connecting your engine (crank case, timing cover, rocker cover) to the inlet vacuum will decrease pressure inside the engine and give slightly better performance (as shown in Vizards book).
  • The decreased pressure will reduce oil leaks.
  • It allows the blowby gases to escape.
  • It allows air to get in when the engine cools down.
  • It will suck out most of the mayonnaise from your rocker cover.
  • Racing cars do it, so it must be good!
Against:
  • The inlet gases will be polluted by the burnt gas and oil being sucked up.
  • The vacuum will be less for servos etc.
  • Extra pipework to worry about.
Well, personally on my 998 I disconnected the pipe from my tappet cover breather to the carb and blocked the carb hole up. I figured that not having burnt gases in the inlet must be good for performance...

BUT, the inlet vacuum is greatest during decceleration when power is not needed, and is nearly zero when the throttle is wide open, so no crank case gas would be sucked in to drop performance.

With my 1275 I'm building I may do away with oil seperator (flame trap) things and just connect the pipe straight on the the rocker cover, timing cover and clutch housing. This would mean a bit of smoke on decelleration due to the sucked up oil but who cares. I've seen lots of minis with this setup and they were all suped up ones.

Scott and Borris (soon to be a mayonnaise powered fusion reactor)

* Mayonaise refers to the mixture of water an oil sometimes found in engines when the cooling system leaks into the unit. M does not provide lubrication. If you find it in your engine, chances are your head gasket is shot. Fix ASAP!
Stolen from the Mini list, 1997, webbified 1998