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Crankcase Ventilation for Blown Engine

15K views 15 replies 9 participants last post by  conny 
#1 ·
I have a 350 chevy with the smaller 142 Weiand blower. The engine has been rebuilt with forged pistons, crank, etc. appropriate for a blown engine. Before I rebuilt the engine, I used to go through rear main seals more often than usual and told that the blower may be creating too much crankcase pressure. The rebuilt engine will be show quality, with many billet parts. My question is what is the best and most attractive way of relieving this pressure? Will adding additional valve cover breathers do the job, or should I consider something else? Any advice would be appreciated.
 
#4 ·
Kind of odd that this post was came up. I spent about 2 hrs this morning researching this subject before I saw this post. Still as undecided as I was when I started. I finally went to Harbor Freight, Lowes and Home Deport looking for a water separator to make a catch can. No luck.

68NovaSS-Are you runing a standard PCV system? Any extra add on's?

There is a lot of info on the net about this subject, with many different opinions and advice, but no definite solution.
 
#5 · (Edited)
For some reason the forum isn't letting me edit my original post to this thread.

I noticed I forgot to mention my engine was also a 350 with a 142.

trifive: I'm just curious but did you build your engine or did you get it from somebody else? I sold my K5 Blazer with that supercharger to a guy in the Navy that moved to San Diego a few years ago. I know it's a long shot but I have to ask.
 
#6 ·
Blazin72 said:
I used a filtered breather in one valve cover and a single PCV valve in the other valve cover routed to the back of the carburetor. If your rings aren't worn out you shouldn't have any issues at all.
Blazin72-Standard PCV? I have read that the crank case can still get pressurized, I don't see how as the carb will always see vacuum. Some talk about running a supra PCV or a Mazda turbo PCV.

I have ran two breathers with no issues, but noticed that my oil gets black real quick.

Not trying to hi-jack this thread I just have the same dilema.
 
#7 · (Edited)
NOlowrider said:
Blazin72-Standard PCV? I have read that the crank case can still get pressurized, I don't see how as the carb will always see vacuum. Some talk about running a supra PCV or a Mazda turbo PCV.

I have ran two breathers with no issues, but noticed that my oil gets black real quick.

Not trying to hi-jack this thread I just have the same dilema.
On a roots blower, the carb on top will always see vacuum around -12. It never goes to zero. On the manifold (under the blower), it will go to 0 and then into boost. Watch where you hook your various vacuum hoses! Power brakes never worked so well off the carburetor, but if you run the vacuum line to your th350 from the carb, you will be in for an unpleasant experience.
 
#8 ·
NOlowrider said:
Blazin72-Standard PCV? I have read that the crank case can still get pressurized, I don't see how as the carb will always see vacuum.
I just walked up to the rack in Auto Zone and grabbed the one that looked like it would fit my application best and stuck it in. Nothing fancy about it at all. Worked great once I installed baffles in the valve covers. Before the baffles I was losing a LOT of oil through the PCV.
 
#9 ·
Believe it or not, I have my PCV hooked to the rear carburetor, on my blown Hemi, (engine in my Avatar) with no breather(s), and it works great. Doesn't suck oil, oil is clean, and I have no oil leaks. I figure that without breathers, the system is only pulling crankcase fumes when ever it needs to, like WOT, idleing, etc. There really isn't any overpowering vacuum while the engine is running, so sucking gaskets in hasn't been a problem...or hasn't appeared to be. Installing the PCV this way has taken care of any little seeps I ever had, and now the engine stays clean. Time will tell, but so far, it works great...
 
#13 ·
I have ran two breathers with no issues, but noticed that my oil gets black real quick.

Not trying to hi-jack this thread I just have the same dilema.[/QUOTE]
With two breathers and no PCV valve, all of the carbon from the blowby gasses stay in the crankcase and turn your oil black and is corosive also . Not a good idea. Install a PCV system to make your engine last longer and run cleaner .
 
#16 ·
Please confirm my question/exploration:
My setup>
305 v8 small block, headers, edel air intake, edel 1406 600ccm, HEI from 301T 79 with pressure switch, pressure sensitive/modified mechanical fuel pump, fuel pressure regulator, performance oil pump, KN air filter, cam stage 2, modified distributor springs and weights, rods and jets prim/sec modified up to .120 secondary, air to water cooler with Bilge pump 30l/min, Eaton Supercharger M112 with pulley making upto 10PSI, blow thru setup - carb in a box, Eaton placed on left side of the engine, blowby setup 8PSI, manual transmission (killed right now - tremec T5), A/F meter with Bosch full scope sensor, pressure sensor intake + vacuum sensor - 2 gauges, AF gauge, oil catch can.

Have no idea about power and torque, T5 lost 4th and 3rd is dying - waiting for 3650 Tremec from Ford.

Question/confirmation>
Right valve cover - PCV, oil catch can, back to edel intake (from middle bottom input)
Left valve cover - went to Air intake in front of Supercharger BUT!!!
I switched it to atmosper and the vacuum gauge showed more stable values, the engine behaves more smooth..

Probably reason:
Right side - vacuum drown from engine / undepressure
Left side - connected to intake of supercharger (right after the filter) / underpressure
So, from both side the engine was forced to produce vacuum all the time, no breathing - no way from to go, all the time it was one way.

After disconnecting from supercharger intake, the engine can take fresh air from one side (no undepressure) and make vacuum from other side. No closed circle.

Is this way better? From my experience - yes.
 
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