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Thread: Can the DrivenFab catch can for our cars be modified to open-dump?

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    Question Can the DrivenFab catch can for our cars be modified to open-dump?

    First, some background for those new to the topic. Evo X's factory design is to recirculate the crankcase blowby gunk back to the intake, so to burn them off. The gunk is recirculated via the breather hose and PCV hose ("ventilation hose") shown below.

    For a modded Evo X, this is unfavorable. More info can be found in this thread of the old forum: https://www.evoxforums.com/forums/sh...d.php?t=151818



    A commonly solution is DrivenFab's v3 catch can/coolant expansion tank, which catches the gunk to be emptied with a turkey baster periodically. My first question is regarding how the DrivenFab catch can works. I searched and can't really find a diagram. I could not imagine the item holds both coolant and oily gunk in one tank. Wouldn't that contaminate the coolant?



    Beside that, let me assume this catch can/coolant expansion tank magically keeps the oily gunk and the coolant separate. It has no vent-to-ground nozzle, but I envision we can maybe install a filter (when motor cools, dirt may enter without it) and then a tube to open-dump the gunk directly to the ground. This saves the trouble of emptying the catch can as frequently as monthly in the winter.

    Venting the crankcase the ground is actually common in cars made before 1970s and among VW enthusiasts (https://www.myfastgti.com/volkswagen...ctly-to-ground).

    Any thoughts on such application?

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    With another thought maybe I'm stupid. Why bother with a catch can? There should be a way to vent to atmosphere/ground directly. I don't entirely understand this, but I speculate maybe I can use an aluminum valve cover modified with a 10AN fitting. The aftermarket fitting vents freely, unlike the factory fitting which closes when intake pressurizes. With a 10AN fitting open-dumping, maybe the breather hose wouldn't even circulate gunk back to intake. Am I right? Am I right?

    More info from chetrickerman:

    Quote Originally Posted by chetrickerman
    If you drill out the stock PCV and install a check valve, it will be just fine.

    It is a better idea to either run both breathers VTA or recirc both back to the intake (pre-turbo)
    Quote Originally Posted by chetrickerman
    The more vacuum (or the least amount of pressure) in the crankcase, the better, so drilling it out as much as you can so it can flow as much as possible is best.

    Your description is of naturally aspirated engines since at higher than 50% (sometimes less) the intake manifold is pressurized.
    Quote Originally Posted by chetrickerman
    Exactly why even with a stock motor you run the breathers VTA or routed to the intake pre-turbo that way crank case pressure can be evacuated via both breathers and not just one at WOT
    Quote Originally Posted by chetrickerman
    Even at stock HP levels, changing the breathers to VTA or recirc both to the intake makes a big difference on cars that I have tuned. Drivability and WOT are a bit better.

    Simply put crank case pressure fights the pistons going down which reduces hp.
    Also this, should I be worried?

    Quote Originally Posted by Yxd68
    If your engine is config'd to VTA crankcase vapors/gases, then the engine oil will deteriote MUCH faster since the closed, type 4 PCV system is no longer available to suck out the combustion gases.

    Back in the day before all engines came with PCV systems and used road draft tubes, the common mfgr recommended oil change interval was 1000 miles.

    Do LOTS of periodic oil analyses and pay particular attention to fuel, water and acid levels in the oil to determine your specific driving conditions and oil change interval needs.
    Last edited by Evo; 07-18-2018 at 08:03 PM. Reason: more info

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    IMHO if you're considering a crankcase VTA system, you're way out of range for a street car.
    The airports had to be commandeered to protect us from the Bowling Green Massacre. Itís what Paul Revere was shouting about as he fired his "second amendment solution" muzzle auto-loading musket into the air again and again and again.

    The truth is that early Democrats used horse-drawn airports to transport kids from Comet Ping-Pong to colonial butter-churning events and other treasonous activities funded by a Colonel Soros.

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    Quote Originally Posted by Yxd68 View Post
    IMHO if you're considering a crankcase VTA system, you're way out of range for a street car.
    UT_EvoX indeed recommended keeping the stock PCV and breather up to 450whp (which is a lot, even MHI 18k with stock block is usually tuned for just 400whp pump gas):

    Quote Originally Posted by UT_EvoX View Post
    In my opinion...
    - Stock power to 450 WHP - fine with stock PCV / crankcase breather so long as you don't restrict the rear valve cover breather hose e.g. kinked hose, extra long hose, adding extra hose and a catch can, small fittings on intake, smaller I.D. hose than stock
    - 450 WHP - 700 WHP - fine with any VTA catch can or Driven Fab AOS (STM also make a nice-looking solution but the check valve being used as a PCV is flawed and flows WAY too much volume which makes idle impossible to control)
    - 700+ WHP - might need to supplement with welded -10 AN fittings and/or oil filler cap breather. > 2 -10 AN breathers may be required to keep crankcase pressure under control
    So I guess I should not worry about the very little oil in the intake pipes and intercooler, and keep the stock PCV and breather, right? Can I say that the oil and blowby vapor being recirculated into the intake is totally healthy and harmless?

    Quote Originally Posted by UT_EvoX View Post
    Stock PCV / rear crank vent
    - Pros: vacuum draw on crankcase brings fresh air into crankcase and aids in turbocharger drainage under idle / vacuum, longer oil change intervals, simple
    - Cons: poor crankcase ventilation under boost as PCV shuts under boost - only one small route out to intake (many intakes restrict this breather further than stock which is BAD), possible oil seal leakage and dipstick popping out under high boost, loss of power due to excess windage in crankcase
    ^ Another possibility I'm thinking about is to keep the stock PCV and breather, but adding a venting spacer of some sort to the oil dipstick. This will function as the third vent from crankcase (will cause tuning issues because of introducing unmetered air into intake). Else maybe work the breather hose somehow and give it a more free-flowing vent into the intake.
    Last edited by Evo; 07-18-2018 at 10:44 PM.

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