Thread: Crankcase Breather Options

The 4BD1 (NA landie/RBG) engine has an 8mm breather in the tappet cover and a ~1" (smallest diameter) breather in the side cover.

The turbo engine (and AFAIK most highway/truck 4BD1 variants) has a ~19mm breather in the tappet cover.

IMHO if you fit a turbo it makes sense to use a turbo breather setup.

You can use a provent with either setup. I made a brass T to connect the two breathers when I first fitted my turbo (free to anyone who wants it).

I later bought a truck tappet cover and side plate from a wrecker.

I spent a bit of time on the weekend stuffing around with the breathers on my NA (but being turbo'd) engine.
I'm fitting a provent, and have decided to connect it up to the original breather on the side cover.
I've extended the fitting on the side cover and reduced the diameter down to 1" to match the provent inlet. Will also tee the 8mm breather from the rocker cover into the pipe on the side cover (but not done in the photo).



The outlet from the provent will be connected back to the inlet between the air filter and the turbo.

Were the factory turbo breathers connected back into the inlet duct somewhere, or just dumped to atmosphere?

Steve

Originally Posted by steveG

Were the factory turbo breathers connected back into the inlet duct somewhere, or just dumped to atmosphere?

Steve

The one I pulled my tappet cover to has a pipe running down to a box type thing on the side, and what seemed to be a vent to atmosphere from there - the engine had been removed from the truck though.

This was my setup (before the turbo tappet cover):



The brass T connected the two breathers, and the pipe then went to the provent inlet.

The one on my ex stage1 engine was the same as that.

I was wondering about the factory turbo breather, if it was plumbed in between the air filter and turbo it would have a slight suction and might make up for the slightly smaller diameter breather compared to the NA one.

Steve

Originally Posted by steveG

The one on my ex stage1 engine was the same as that.

I was wondering about the factory turbo breather, if it was plumbed in between the air filter and turbo it would have a slight suction and might make up for the slightly smaller diameter breather compared to the NA one.

Steve

No - sorry if I was unclear. The pics I posted were of my landie breather. The truck breather is completely different.

This is a truck breather (though different to the type I have seen).

The connection at the top is the breather coming in. The larhe hose at the bottom vents to atmosphere and the small hose drains oil to the sump.

There is no intake connection AFAIK. Truck engine manufacturers avoided running (unfiltered) blowby gases to the intake unless it was mandated by emissions (as the soot damages turbos etc).

Only if you have highly efficient CCV filter like the provent is it a good idea to run the breather to the intake.

Some of the truck setups ran that breather from the can back into the intake. Depended on the market and year the engines were sold into.

Originally Posted by Dougal

Some of the truck setups ran that breather from the can back into the intake. Depended on the market and year the engines were sold into.

Yes - when emissions regs mandated it.

However AFAIK the breather hose sizes didn't change between open and closed systems?

Originally Posted by isuzurover

Yes - when emissions regs mandated it.

However AFAIK the breather hose sizes didn't change between open and closed systems?

Yes exactly the same hose sizes. The hose just took a trip over to the left and joined the intake.