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Rb26Det Exhaust Scavenge Build

Slidewayzzz

By Slidewayzzz,
in Fabrication

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Slidewayzzz Apprentice

Slidewayzzz

Posted
Posted

Thought id give it a try, been thinking about it for months now and i just cant seem to find the info i need, so i decided to start a build thread.

Firstly im making a custom baffled catch tank that 2 scavenge kits will be hooked up to from my turbo down pipe creating vac esp at high rpm. I know there must be no back pressure for it to work correctly and luckily i have a free flow all the way through.

On the catch tank will be a vac relief valve to relieve at a certain vacuum (if at high revs it draws too much vacuum), a 1way/check valve to get rid of any positive pressure in the system and a boost/vac gauge to see whats happening.

I know there are easier ways to get vac on a catch tank but i dont want any blow by gasses sucked back into my intake system.

Let me know what you guys think

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89CAL Grand Master

89CAL

Posted
Posted

won't that pressurise the catch can and therefore the head (through the cam cover breathers) when under high load/rpm due to exhaust backpressure?

I know you said you have no back pressure, but have you actually put a gauge on it? I'd be suprised if you hadless than 2psi back pressure at full boost. Depends on what turbo/exhaust you are running, but I'd be very suprised if you had 0 back pressure

GTRNUR Grand Master

GTRNUR

Posted
Posted

The only exhaust scavenge setups I have seen work are on race cars that run no mufflers. The moment you have a post-turbo restriction of any kind, you end up with a higher than atmospheric pressure inside your exhaust (after the turbo).

Remember you are trying to produce a vacuum, not just aid flow from what is already a high exhaust pressure (such as venturi style wastegate scavenging).

Using a 2 stage catch can setup that draws from a venturi on your Intake just before your turbo will produce a vacuum in the engine. Your first catch can had better return to sump though, or your vacuumed up oil vapour will quickly make a mess on the inside of your intake piping.

Slidewayzzz Apprentice

Slidewayzzz

Posted
  • Author
Posted

Thanks for the comments. Seems like there are some issues i overlooked.. As 89CAL stated, its likely to have slightly positive pressure at high rpm/boost :verymad:. Starting to think along the lines of a vac pump or pre turbo vac line that draws from my sump (the highest point of sump on drivers side). In my head it should kind of promote faster oil drain from the head down to the sump, instead of drawing out the cam breathers decreasing oil return? Making more sense?

Pre turbo vac source would have to have sufficient baffleing/oil air separation though.

Might even work using my rear turbo oil drain as a place to introduce the vacuum to (no longer in use, rb26det). Then again as far as i understand the passenger side of the motor has a natural vac at rpm, which wont help me at all.

Any problems you guys see with this please give me a shout as i have to make a plan by the end of the week, powercruise is getting closer

Thanks again

89CAL Grand Master

89CAL

Posted
Posted

Not so much a problem, more so a question. Are you over thinking things?

I know your probably trying to do something different to find a new way to do things, but wouldn't a baffled catch can with sump drain and vac from the intake work fine?

Ben C34 Grand Master

Ben C34

Posted
Posted

There is a way to ensure the exhaust scavenge system works, even though it's pointless, is to put the venturi pretty much at the end of the exhaust, the last 300 mm or so where there can't be back pressure.

Slidewayzzz Apprentice

Slidewayzzz

Posted
  • Author
Posted

I sure have been over thinking things it seems. And yea i kinda did want to do something different but this car is draining the life out of my wallet now so im simplifying it.

Just going to get vac from my intake pipe and route it to my block somewhere with an air/oil separator in between. Possibly another intake pipe - air/oil separator - cam cover breathers.

Options i have on my block are; 2nd turbo oil return, dip stick or unused -10an sump bungs (came with the rips high cap sump, high as possible and at the front drivers side).

Thing is i just fully rebuilt and on my last hard pull through all the gears on high boost it spat some oil out the breather on the cam covers at the top of 4th. I think its mainly because im only running a filter on one side and the other goes to the stock place (plenum side just above fuel rail) that only sees vac at idle. I will be getting some mines cam cover baffles too and see how that goes.

Anyways cheers

GTRNUR Grand Master

GTRNUR

Posted
Posted

The best solution you have is to use a catch 3 hose catch can (each cam cover, and the intake), and a return to sump via the -10 RIPS sump return. Hi Octane have the catch can you need to complete this setup. Not cheap though.

The return to sump via the 2nd turbo return on an RB26 block works great too. Nismo pioneered this of course. You can improve on it by drawing the intake connection through a second catch can and then to the intake. Useful if you are really trying to isolate all moisture from your crank case fumes.

  • Like 1
  • 1 year later...
Stoney85 Collaborator

Stoney85

Posted
Posted

Read the oil control issue thread, and just do a catch can setup like that.

An exhaust scavenge setup can work and has been shown to work, usually on N/A cars though, but for your setup, it's probably not required and over the top.

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