Guidelines For Catch Can Volume, And Dedicated Sump Breather

[Scooby]

G'day everyone

Done a search, even found an old thread I started years ago on this topic but at that time no one really seemed to know the answer. Car is an R32 GTR. We've all seen catch cans that vary in volume from the Nismo oil/air separators that are prob the smallest, to the Greddy type, to the type that mount in front of the battery on an R32, to the type that displace the battery on the 32 all together and are prob > 2 litres volume. Anyone have any evidence-based recommendations for volume?

Also wondering if anyone is running a dedicated sump breather line that goes from the sump to the catch can?

Cheers

[black bnr32]

do you plan on venting back into the intake?

[Beer Baron]

I use 3L can. some racing classes have a formula for catch can size based on engine capacity. the reason being if the engine goes bang how much oil/crap can it pump out before it's shut off (to help prevent oil downs on the track).

for an RB26 3L is fine and can fit in front of the battery no problem. sump breather is a good idea. from standard they do breathe through the oil galleries so whether you run the breather from sump up to the covers (which is then vented to a can) or direct to the can it doesn't really matter.

[Scooby]

Presumably a sump breather can only work if it's vented to atmo? Otherwise it'd be sucking out of the sump on boost.

[The Bogan]

I believe that sucking from the sump is called scavanging which creates a low pressure zone in the sump which in turn releases more power,like a dry sump set up.

Look in the thread about dry sump, lots of cool physics and other cool stuff, good read.

My boat has a 3 ltr can, sump vent / drain back, a lot has to do with the design of the can or more importantly the inside of the can and having return drains on the hot side.

Also the breather at the can needs to be big enough so it doesn't impede the flow.

[Duncan]

Cams schedule B section 15 says"

if fitted with any crankcase breather discharging to the atmosphere, each breather be vented into a catch tank of minimum capacity of two litres for engines up to 2000cc or three litres for over 2000cc. Regulations for competitions on unsealed surfaces may waive this requirement;

That is a fair guide to start with.

I'm not sure why it is based on engine capacity not oil capacity but meh!

[Beer Baron]

yep, hence the 3L can on my GTR. I asked the same thing, thinking that a 9L sump still has a lot of oil to spew after the 3L can is full but it's something to do with oil getting into the cylinders and getting pumped out by the now dieing engine. plus not many people could fit a catch can as big as their sump! not sure where we'd put 9L cans...