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Discussion Starter #1
I cant find any solid info on valve cover venting for a sohc. Im at the point where I need to paint my VC but would like to be sure I have the vent in order so I dont mess up the paint with any mods if need be.





Basically the stock VC vents is .250" ID, off the back left corner. And I can run a line straight from that to a catch can, or I can probably even drill that hole out to .350 or so, there is a sleeve pressed in it that may be a PITA and I cant see much inside behind the oem baffling.

Do you guys think its really necessary to mess with venting and add any bungs/barbs off the front of the VC??
 

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Two men shy of a group
99 civic sedan ex
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i would say it depends on the piston rings and other stuff probably since worn out rings will let more blow by gas through, also probably need it after a certain hp range but those are just my guesses. right now im make 166hp and 149 tq and i just have my valve cover venting to atmosphere until i get money to build a catch can setup
 

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ej8
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Why does the oem factory honda air box blow fresh air into the valve cover?
Yes i know it puffs air out when you rev the car but on the pcv diagram it shows that air in pushed into that hole on the vc.

Yea i know random, but anyways i just have hoses coming off and pointing to the ground. Plan to make a catchcan and have some kind of vacuum on it just havent gotten around to it.
 

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98 Civic CX-T on E85
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it really depends on your hp goals...i would say anything lower than 300whp or so you can probably get away with the oem vent port...higher hp cars need more venting because of build up of crank case pressure, in which you should vent both the block and the head. the way i figured out i needed more venting in my engine was i started blowing the dipstick out of the tube.
 

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Why does the oem factory honda air box blow fresh air into the valve cover?
Yes i know it puffs air out when you rev the car but on the pcv diagram it shows that air in pushed into that hole on the vc..
If the pcv valve is open and the engine vacuum is drawing in crankcase air(stock system), it needs to have a fresh air inlet to be able to move air through the crankcase. If you try and breath with your mouth closed, nothing happens, if you open your mouth and breath, you can move air.
 

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1988 Honda CRX
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You can't have to much venting but you can have to little.

The hose going to the air duct does not blow air into the crankcase. If the crankcase is lower than atmospheric pressure due to the PCV aiding in manifold vacuum drawing a vacuum, then air at atmospheric will flow in.

Even at WOT on a running NA engine, the air pressure in the plenum will be at least slightly lower than the air pressure in the air duct so FILTERED air will tend to be sucked into the crankcase from the air duct and back out the PCV into the plenum. On a boosted engine as soon as you get into the slightest hint of boost, the PCV no longer works and you only have the vent to the air duct to vent blow by. Also boost increases blow by, no matter how good your rings are. There cannot be a perfect seal due to ring end gap and ring clearance in the groves and the change over from the rings sealing against the top or bottom of the grove as the piston changes direction at TDC and BDC.

More cylinder pressure from more compression and/or boost means more blow by through the same gaps.

Short story. On any boosted engine or even any significantly upgraded NA engine you certainly benefit from bigger vents. I would think for a 200hp turbo engine you want at least double OEM venting. That is double CSA (cross sectional area), not double dia. Doubling the dia. of a vent pretty well quadruples the CSA.

CSA equals internal dia divide by two.
Them multiply that by itself.
Them multiply by Pi or 3.1416

ie

1/4" dia = 1/8" rad or 0.125" rad
0.125 X 0.125 = 0.0156
0,0156 X 3.1416 = 0.049 sq inch

1/2" dia = 1/4" rad or 0.25" rad
0.25 X 0.25 = 0.0625.
0.0625 X 3.1416 = 0.196 sq inch

Venting to open air works OK BUT:-

1) Oil mist is carried to your engine bay and to the air and road surface and drip off the engine bay onto your garage floor or drive way where it might be trodden on and walked onto your carpet as you enter your home. At best grubby. At worst antisocial self interest with no regard for the community.
2) The air sucked back in the vents as the pressure pulses is not filtered so you suck dust and crap back into your engine crankcase.
3) The oil is not collected and possibly returned to the engine so it can cause an increase in apparent consumption.

You do not need to vent both valve cover and crank case as they are already connected by large passages via the oil drain back holes.

The higher in the engine and the more isolated from the crank, the less oil will be carried in the fumes. that is why OEM puts it in the VC with a big baffle under it. Draw from behind that baffle, just use bigger vents. Remove tha baffle to properly clean schwarf out of the VC then replace the baffle. That involves removing the riverts and threading the rivet holes in the VC so you can use bolts in place of rivets.

Use a catch can with a filter on its vent.

For a DD connect the bottom of the catch can to the black box or the black box port in the crank case.

For a pure race car use a bigger catch can and do not drain it back so you can gauge engine condition between rounds by changes of oil volume collected each pass.
 

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1988 Honda CRX
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NO

I am saying all vents should be from the top of the VC and should go to the side of the can fairly high up. The filtered vent for the can should be out the very top of the can and a drain should be from the very bottom of the can back to either the top of the black box if fitted OR to a fitting to the port where the black box normally fits to the block or crankcase.
 

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ej8
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NO

I am saying all vents should be from the top of the VC and should go to the side of the can fairly high up. The filtered vent for the can should be out the very top of the can and a drain should be from the very bottom of the can back to either the top of the black box if fitted OR to a fitting to the port where the black box normally fits to the block or crankcase.
yea i think i said that lol.

The pcv hose goes to the black box. So if i remove drill out the pcv. Do i run that hose to the bottom of the catch can or to the side.

and vc to the side and filter on very to right.
 

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OK

I was presuming the PVC would be repositioned to the VC and the hole in the top of the black box was vacant. Yes run from the bottom of the catch can to the old PCV hole in the top of the black box. If you retain the PCV, move it to the VC behind the baffle.

If you have gone to the extent of fitting a turbo, welding a breather bung into a VC is really minor stuff. There are ways without welding that involve fittings and threads and screws and silicon rubber sealant, but they tend to be ugly and not as tough as a weld.
 

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I saw that DIY. A few things I don't like are the JB weld and PVC tubing.

PVC turns to a soft rubbery goo at about 90 deg C. A turbo under bonnet (hood) temp can go hotter and the clamps will go loose as the PVC compresses under them.

I would braze or silver solder that fitting into the black box rather than glue it in with epoxy. I guess JB weld is an epoxy with a clay or talk filler. Plastics like epoxy expand at a different rate to steel, so temperature cycle tends to separate the joint.

I like an oil drain back to the engine on a DD. The manual drain and collect to inspect is good for dedicated race cars though.
 

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()*#$(*$
93 Legend L Coupe.
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SO pat pretty much ruined my chance to reply. Thanks, Pat. LOL!

If you race at any track/strip that gives a darn, you cannot just vent the PCV to the ground. That becomes a hazard if every car is misting the track with oil vapor.

A good catch can will condense most oil vapor.

I hate the idea of having to empty a catch can, so a drain back is, IMO, much more ideal than having to empty a can that, if something does go wrong, will just overflow and dump oil everywhere. (It happens, especially in racing.)
 

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If this is a turbo setup, i would try and stay away from putting anything on the block vent or ensure you use the black box for baffling. The block vent sees alot of oil activity. Ive had a lot of different attempts, and the one thats worked the best is 10an fittings off the back of the valve cover under the stock baffling to a vented catch can, the block port plugged, and if you want to return oil, put a fitting in the oil pan and run a line off the bottom of your can to the pan. I have a line off the bottom of my can down to a 1/4 turn valve so i can stick my hand under the car and drain my can easily(no return).
 

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Something that I've seen on race cars is a smog pump one way valve downstream of the cats/ o2 sensors and the exhaust volume leaving scavenges the pressure from the crankcase. Obviously thos isn't the environmentally friendly way to do this, just an option.
 

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Discussion Starter #19
Yes my local track does not allow to vent to the ground, but they honestly dont check hard, if they cant see the ends of the hoses they probably wouldnt notice, but I also want to be safe.

I think what im going to do is this, drill out that existing valve cover vent to .375", and for the block, I have already deleted the "black box" and have a 5/8" ID barb jb welded in the block. So Im simply going to run vent hoses from both block and head, to a vented catch can.

I wont be running a PCV valve, any problems with that?? On a boosted car obviously
 

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Even on a boosted car, a PCV helps a bit in off boost cruise, but is of no help at all in boost and if the non return valve built into it fails, you fill the crankcase with boost pressure sand maybe blow out a few oil seals. Very unlikely but possible. I am pretty sure most OEM turbos still use a PVC.
 
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