Crankcase ventilation on a supercharged engine

flatjack9

flatjack9

Well-known member
I built an engine for a customer and he has since added a supercharger. Now he is getting some oil seepage. Looking for recommendations on a viable breather system. All he has now is the breather on the oil fill tube.
 
I get leakage on my rear main seal with my SBC and McCulloch VS-57 supercharger (5 psi). Minimal leakage if I don't get on the SC but more than I'd like when I'm on the SC often during a ride. Maybe 3-4 tablespoons.

This SBC is a 65 with a vented fill cap, vents in each valve cover and a ME WAGNER PCV
http://mewagner.com/?p=444
PCV is piped from the rear road draft and discharge is through a water/oil separator then into the base of my Holley 4150 carb.

Glenn
 
Every engine has crankcase pressure caused by the pistons on the down stroke into the crankcase as well as the pressure from compression getting past the gaps of the compression rings. Boost pressure from the blower is of course adding additional pressure into the cylinder so now there's even more pressure going into the crankcase. A way is needed to vent this pressure the easy solution is a PCV valve. Or some type of additional bottom end breathing that allows the pressure build up in the crankcase to escape. A vacuum pump helps in a situation like this if it is installed correctly.
Ronnieroadster
 
Ronnieroadster said:
Every engine has crankcase pressure caused by the pistons on the down stroke into the crankcase as well as the pressure from compression getting past the gaps of the compression rings.
Click to expand...


Hey Ronnie....You know, I totally understand the concept of blow-by getting past the rings to pressurize the crankcase. But this is not the first time I've heard it stated that pistons moving in a downward direction effectively cause a rise in crankcase pressure. I continue to find it impossible to disregard that for every piston moving DOWNWARD, there is an equal number of counterpart pistons methodically moving in an UPWARD direction, especially in the case of 4-cycle engines. So, if the DOWNY pistons are creating additional crankcase pressure, why is it that the UPPY pistons are not sucking-away at that additional DOWNY pressure, hence.... creating an equal amount of SUCK, to negate and subtract from the undesirable positive pressures created by the DOWNERS? If even there was a check valve involved somewhere in the beast, but there is NOT! Learn me something here, please!

Coop

.
 
Coop very good question. It would seem the upward piston movement would give the effect of a vacuum which one would hope would eliminate or reduce the crankcase pressure but that's not what we see.
If the upward movement had the sucking power we then would have another big issue. Oil or oil vapor from the crankcase being sucked upward.
Some of todays production engine's have piston squirter's the squirters shoot oil up into the chamber directed so its hitting the inner top surface of the pistons. This oil helps to cool the tops of the pistons due to the lean burn causing a hot piston top surface. The high temps are caused by the trend for better economy. If the upward movement had any sucking power the squirter idea would not be necessary. I have considered piston squirters on my competition flatheads to help reduce the piston top surface temps.
An added note and advice.
Once a vacuum has been applied to the crankcase the suction can be so high that the piston wrist pins are in danger of loosing oil creating another problem. There's a delicate balance needed at times to help reduce this pressure.
The mystery's of the internal combustion engine can be endless at times.
Ronnieroadster
 
Ronnieroadster said:
Coop very good question. It would seem the upward piston movement would give the effect of a vacuum which one would hope would eliminate or reduce the crankcase pressure but that's not what we see.
If the upward movement had the sucking power we then would have another big issue. Oil or oil vapor from the crankcase being sucked upward.
Some of todays production engine's have piston squirter's the squirters shoot oil up into the chamber directed so its hitting the inner top surface of the pistons. This oil helps to cool the tops of the pistons due to the lean burn causing a hot piston top surface. The high temps are caused by the trend for better economy. If the upward movement had any sucking power the squirter idea would not be necessary. I have considered piston squirters on my competition flatheads to help reduce the piston top surface temps.
An added note and advice.
Once a vacuum has been applied to the crankcase the suction can be so high that the piston wrist pins are in danger of loosing oil creating another problem. There's a delicate balance needed at times to help reduce this pressure.
The mystery's of the internal combustion engine can be endless at times.
Ronnieroadster
Click to expand...

Hey Ronnie..... As Judge Haller replied in My Cousin Vinny.... "That is a lucid, well thought-out, intelligent explanation...."! I really appreciate you going to the lengths that you did to try to explain this phenomenon in terms that actually make some sense. And even if I haven't completely wrapped my head around ALL that you had to say here (yet), I can't think of anyone else offhand that I'd be more inclined to believe with such a plausible clarification on the subject. Thanks again, Ronnie! YOU know some stuff, yeah?

Coop

.
 
SBC venting for SBC in my 40 Ford

502704


502705
 
glennpm said:
SBC venting for SBC in my 40 Ford

502704


502705
Click to expand...


I know that a guy must take his crankcase ventilation pretty seriously to spring for one of these "SPENDY" adjustable PCV Valves. Does it deliver anything like the results that you had hoped for, Glenn?

Coop


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Coop, I spent $$$s on it and it works great :-), like my sons tell me that their car/trucks run better after they change the oil :-))

The thing I liked about this is the ability to set two settings with vacuum readings taken, to control idle and then cruise. It helped a lot in oil leakage blow-out during boost versus the road draft hose I had dumping under the car. From Wagner web site:

"Benefits:
• Fully tuneable to your engine combination
• Adjustable flow rate can be tailored to your engine’s setup, allows controlled incremental flow rate changes
• Adjustable vacuum transition level can be tuned to your engine’s unique vacuum profile
• Properly ventilates crankcase, resulting in cleaner oil and cleaner engine internals
• Reduces crankcase pressure, which is often the cause of oil leaks
• Eliminates in-car oil smell while driving
• Works well with air-oil separators
• Reduces emissions
• Reduces moisture and acidic vapors in your engine’s crankcase
• Vacuum gauge tuning method ensures PCV system is set properly for your combination

Tuning with Dual Flow Technology:

Eliminate the guesswork from your PCV system! Dual Flow PCV Technology gives you full control over your tuneup. The Dual Flow PCV Valve has independent idle and cruise circuits, each of which are adjustable.

The idle circuit’s flow rate can be tailored to your specific engine combination. The Dual Flow PCV instruction guide includes several starting points for idle flow rates based on engine size and idle vacuum levels.

A properly functioning PCV Valve will increase its flow rate under cruising conditions to accommodate additional blowby produced under higher load conditions. The vacuum level where the PCV Valve transitions from a low flow idle mode to an increased flow cruise mode has always been a source of guesswork, and is a critical component of your tuneup. Dual Flow PCV Technology allows the user to precisely set the idle to cruise transition point.

Question: I'm running a centrifugal blower I turbocharger I blow
through carburetor. Can I run a Dual Flow PCV Valve?

Answer: Yes. In this application the PCV line will be under positive
pressure under boost conditions. We reverse flow test every Dual
Flow PCV Valve to 20 PSI as part of our QC process. Our experience
has shown that the Dual Flow's design has better backfire protection
than any stock valve tested due to its check ball design.

Glenn
 
Ronnieroadster said:
Once a vacuum has been applied to the crankcase the suction can be so high that the piston wrist pins are in danger of loosing oil creating another problem. There's a delicate balance needed at times to help reduce this pressure.
The mystery's of the internal combustion engine can be endless at times.
Ronnieroadster
Click to expand...

Hi Ronnie,

Thanks for your writeups. I have teflon buttons and no wrist pin clips in my SBC. The machine shop I used built lots of race motors and he suggested them. He did all the blue printing and balancing and I did the assembly many years ago now :-)

I also recently looked into vacuum pumps for the oil pan especially the electrically operated ones but they are big bucks!

Glenn
 
I put an old fashioned curved valve cover breather on the right front of the oil pan with a baffle on the inside to keep oil splash away. Never had a problem with this setup.
 
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