hey, it's me again... what's the point in a catch can? and, where do all the lines come from/to?

...been in the game for a while, just always flew under my radar...

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by jayswat91 &raquo;</TD></TR><TR><TD CLASS="quote">hey, it's me again... what's the point in a catch can? and, where do all the lines come from/to?

...been in the game for a while, just always flew under my radar... </TD></TR></TABLE>

It is an improved system for the PCV (positive crank ventilation) valve, basically you're wisking away crap oil from the head and making sure everything breathes properly.

Oil lines usually come from the back of the block near where the crank is, where the PCV would sit and from the head, I believe.

This could all be blantantly false, but that's my understanding. Could try searching for an explanation.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by jayswat91 &raquo;</TD></TR><TR><TD CLASS="quote">hey, it's me again... what's the point in a catch can? and, where do all the lines come from/to?

...been in the game for a while, just always flew under my radar... </TD></TR></TABLE>

catch can is used to catch oil vapor.

the engine is desigend stock to route any blowby (internal gaseous mix from combustion leak through the piston rings and pressure inside the crankcase) back into the intake to be burnt up. this is for environmental reasons.

this flow is regulated by a PCV (positive pressure crankcase ventilation) Valve. on our engines, it sits in between the #1 and #2 intake runners on a MPFI intake manifold (i dont know where it is on a DPFI). there is a black box that is baffled at the back on the engine. its designed to help separate the oil vapor, but doesnt do an adequate job really. that is connected to the PCV valve, which is then routed to the top of the intake manifold. the big hose in the middle.

"fresh" air is supplied into the engine through the valve cover from the air intake arm. however, when blowby is excessive and/or at WOT, flow will reverse through this opening and straight into the throttle body/intake. so there is no oil separation, and it just dirties your intake. over time, it builds up. also, unburnt fuel and oil in the intake air increases the air/fuel mixture and will result in effectively lowering the octane level of the combustion decreasing the chance of detonation. especially harmful on a turbo car.

the catch can just collects any condensed liquid (fuel/oil), instead of dripping on the ground, or over your engine bay. the most effective way to use a catch can is to NOT route any hoses back into the intake. simply vent the blowby gas to atmosphere after its gone through the catch can.

run a hose from the PCV valve (or bypass it completely from the engine/baffle box) and from the valvecover nipple to the catch can. then plug up the nipples at the intake manifold and intake arm. some engine builders will just plug up the back of the engine completely and just rely on the valve cover nipple to vent any of the pressure.

some still want to route it back into the engine. seems kind of pointless to me personally. the point is to prevent the oily air from going back into the engine, so why even route it to the engine... it doesnt need the vacuum from the engine to suck the air through. the crankcase provides the source of positive pressure already.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Tyson &raquo;</TD></TR><TR><TD CLASS="quote">
some still want to route it back into the engine. seems kind of pointless to me personally. the point is to prevent the oily air from going back into the engine, so why even route it to the engine... it doesnt need the vacuum from the engine to suck the air through. the crankcase provides the source of positive pressure already. </TD></TR></TABLE>

My understanding is if you are using a properly baffled can to separate all the oil vapors, you can route a line back to the manifold to get vacuum or to a slash cut in the exhaust. I have only seen dyno charts of v8's, but having the crankcase under vacuum can add horse power. Some use vacuum pumps instead of relying on intake/exhaust vacuum.

 

ive never even heard of it routing it back to the exhaust. cant say much about huge mega power engines, its not really my thing. just from all the honda's and other race engines ive seen built properly.

the crankcase creates its own positive pressure. (ie positive pressure crankcase ventilation) it doesnt need to "suck" anything.

if those big engines benefit from negative pressure, then so be it. i think we're talking about 1.6L 100hp engines here.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Tyson &raquo;</TD></TR><TR><TD CLASS="quote">ive never even heard of it routing it back to the exhaust. cant say much about huge mega power engines, its not really my thing. just from all the honda's and other race engines ive seen built properly.

the crankcase creates its own positive pressure. (ie positive pressure crankcase ventilation) it doesnt need to "suck" anything.

if those big engines benefit from negative pressure, then so be it. i think we're talking about 1.6L 100hp engines here.</TD></TR></TABLE>

totally agree with you I have my catch can routed the way you explained actually.
there are some benefits to a crankcase under vacuum, but probably not worth it on a honda.