Review Legacy BP5 Catch Can Setup

[sleepr]

Hi team,

I just thought I would review my catch can setup, especially after meeting @Kiwi_Fozze on the club sub meet night.

Car in question is my 2004 subaru legacy bp5. The intake pipe to the turbo is straight pipe and with nothing entering the intake, no maf either.

 

I have attached my awesome paint diagram.

 

The diagram is as if you are standing in front of the car and facing the engine.

The front ports on either side of the heads (marked with black box) are blocked.

The pcv not shown is also blocked.

 

The driver's back head port is T with crank case port and goes to the catch can

The passenger back head port goes to the other port on the catch can.

 

After looking online, this setup looks wrong. Please advise.

[Gripless]

 

Read the discussion around page 48 +- a few pages.

Lots of good stuff 🤔

 

[Andy_Mac]

 

Why are the front ports on the heads blocked? They apparently work well at equalising pressure between the two heads.

 

Teeing the two heads And having the crankcase separate is the better method.

 

Does the catch can just vent to atmosphere? Without it attached to the intake there won't be a heap of flow, most of it will be from the crankcase so you'll probably end up pushing any oil from the crankcase back into the drivers side head eventually.

[sleepr]

Cheers @Gripless will have a read.

 

@Andy_Mac No idea why it's done that way. It's done by @Subirex Automotive

 

Will get them to correct it.

 

And yes the catch can vents to atmosphere.

 

So leave the front ports blocked? And T both back head ports and run to 1 port and then the crank case to another port. I do smell a lot of fumes in the cabin so I always have to keep the ac mode into internal.

[Andy_Mac]

Could use an inline filter and extend a line down by the trans like the IAG race AOS to try reduce any odours.

 

From factory the second ports just cross between the two heads to equalise any pressure which will help with emptying a head back if it fills when on the track.

I asked Tony a while back about deleting them and he was strongly against it. This is with vacuum pulling the oil out of the heads which yours won't have so may not be an issue I guess.

[Kiwi_Fozze]

I'd be looking to reinstate pcv...

 

Rear ports on the head should go to catch can.

 

Front ports should tee together and to the right hand side crank case breather if you have it, as a pressure balance system.

 

The pcv should also go back to the catch can, and there should be a consistant vacuum on the catch can. 

 

Or you could set up some sort of exhaust Venturi to put vacuum on the can, I'm sure there was talk of that previously, along with a soopercooler....lel

[Andy_Mac]

Just had a chat to Tony about this. Joining one head to the crankcase isn't a major and is apparently quite a common way to do it.

 

Front ports are the ones with the head baffling so are the ones to connect to the catch can. The rear one's are the ones that should have the factory balance system attached.

 

Here’s how mine is. Front port goes to tee then AOS.

 

[sleepr]

Oh bugger, then what to do with the back ports? Just T them up like @Kiwi_Fozze said for the balance?

 

So plan is T both the front head ports to one port on catch can and then separate the crank case and run to the other port on catch can. Leaves me 2 back ports. Hmmm

[Andy_Mac]

Try find the factory back lines from a wreck as the centre piece is hard plastic so will fit nicer than just hoses run across. Wonder what has been done about the second crankcase breather port on the right

[Niran]

Yeap. Back ports need to be hooked together. Front ports go to catch can. 

 

I hate that my breathers plug back into the intake. Oil should not be going in there. Will be going with a AOS that doesn't plumb back into the intake for the next build. 

[pl0x]

Mine is set up with the two non baffled tee'd together, other two and crank case breather to the catch can which vents to atmosphere. It stinks, I plan on running a tube down so it vents under the car.

 

Didn't only the later blocks (grb onwards) have the other crank case port, which you would tee and plumb the non baffled ports to.

[Kiwi_Fozze]

On 16/09/2019 at 2:01 PM, pl0x said:

Mine is set up with the two non baffled tee'd together, other two and crank case breather to the catch can which vents to atmosphere. It stinks, I plan on running a tube down so it vents under the car.

 

Didn't only the later blocks (grb onwards) have the other crank case port, which you would tee and plumb the non baffled ports to.

Nah v7+ had em, think even the v5/6s had em too