14 replies to this topic

[Jackman]

I was wondering what the benifits of having the engine breather connected to the carb and whats the benifits of not having it connected.

Its currently connected and its sucking in alot of oil vapour at the moment. So what do you suggest.

[Guess-Works.com]

Either, I vent mine to atmosphere using a filter

[Bungle]

and me :grin:

[Jackman]

Well i have read a post saying that it help suck mayo out if there is an and other things... just want to know what would be best.

Post

[wobbit]

will i need a breather if i get a cone filter?

[Pooky]

Where do these breathers go and what do they do?

They look cool! :cool:

[Guess-Works.com]

One minor oversight that that post has forgotten to over look...

Crank case presure is neither constant and not always positive, but the main thing is the more breathers you have the better, as that last thing you want to do is restrict airflow into and out of the crank case as this will sap power.... It's also a good idea to vent to a catch tank if you're going to do trackdays !

[Jackman]

... ive only got one breather out of my engine... Also i wont really be used for trackdays and i dont get this pressure stuff lol. Can you explain?

[kada1980]

Just open up a can of worms, :grin: Where does crank case pressure comes from? positive or negative? If you think about there shouldn't really be any.

[miniboo]

i am sure i read somewhere that it is actually illegal to vent breathers direct into the atmosphere!

might be wrong though

[minimanclive]

I found with my old 998 engine that if I ran with the breathers vented that the gearbox leaked more oil than ever. With the breathers connected it leaked much less. So I leave them connected.

[Jackman]

Im going to leave it connected... can you get more breathers for 998's or is it just the one on the back of the engine?

[Slimer]

This may be stupid but what is the difference between a cone filter and a breather?

[Bungle]

the cone filters are for the carb and the breathers are for the oil :smartass:

[chairchild]

Right then - when a piston is on the compression stroke, it has to squish a lump of air/fuel into around one tenth of it's original volume (depending on compression ratio) This creates a fair bit of pressure on the piston rings.

Now when the fuel/air mixture is lit, this pressure increases to silly levels, so some of this will vent around the piston rings, and into your crankcase


This is where you get crankcase pressure from - it's all the gasses that have squished out from around the piston rings, into the crankcase. The better the seal from your piston rings, the less crankcase pressure you'll get!

Also, when you heat up oil, and splash it around everywhere, you'll get some rather nasty fumes.



Now you really dont want to try and contain it inside the crankcase, as it creates additional work for the engine to do, and will end up blowing a few seals. The answer is to do one of 2 things, either vent to atmostphere, and let it push itself out, or connect it to a source of vacuum, and suck it all out.





So now we're faced with a problem, you can either:

#let the engine suck it all out, by connecting it upto the standard breather hole in the carb, and have the benifits of less crankcase pressure, but a lower fuel octane rating (oil reduces a fuel's effective octane rating).

#vent it to air, have NO oil contamination to the air/fuel mixture, but a minimal amount of crankcase pressure, which is still a performance drawback


There is also the evacusump setup (as explained in vizzard) which uses the velocity of the exhaust gasses to create a large vacuum inside the crankcase (GREAT for power and efficiency!) but it does have the drawback of only being able to operate at higher rpms, and making your hydrocarbon emmisions a bit higher when it comes to the MOT - as all the fuel that leaks past the piston rings, is now being sucked directly into the exhaust :saywhat:



For most people driving everyday cars - it's easiest to just keep it as standard, as the performance increase is minimal. But theres no reason why you cant use the little breather filters if you want to make your engine bay look shiner - just be warned that they'll still make a small covering of oilly residue all over your engine!

A way to get around THAT problem, is to use a catch-can.........


A catch can is just a big can - which changes from the standard breather piping, to a large area, which creates a small pressure drop. The drop in pressure causes the oil/nasty gunk to form into droplets inside the can, and the output then has a small filter on it as well. They give off much less atmospheric pollution (to all you eco-bugs out there) and have the added bonus of looking nice if you can get your hands on a chrome one!














hmmmm - not bad for a first post eh? :wink: