I have a fresh rebuilt 350 with twin turbos. Both turbos are not mounted high enough to properly gravity drain oil back to the pan so I installed a reservoir and a scavenger pump to pump the return oil from the turbos back to the fuel pump mount since I have an electric fuel pump. My problem is that I am getting excessive blow by. Does the scavenger pump push too much pressure into the crankcase thus causing excessive blow by? Do I need a vacuum pump to remove this blow by in the crankcase? Do I need check valves? Do I need regulator to manage the pressure from the scavenger pump? Need some advice and recommendations.

 

You need -10 minimum oil returns from each turbo with no sharp bends to slow down flow. Is your crankcase well ventilated? Open breathers is as open as you can get .

 

My experience. If they are standard tension or stock rings. The rings most likely done. IMO

 

I don't hardly think so with 40 miles on the rebuild.

 

Pull the down pipe and charge pipe and check for oil there. Are you sure it’s “blow by” or are the turbos blowing oil into the exhaust or intake?? Have a picture of the setup?


Is the reservoir vented? You should not have your oil evac pump “pulling” oil. Gravity drain into a reservoir with a vent. Then empty the reservoir. Pumping the oil back into your crank case will not cause blow by. What pump are you using to pump the oil?


I don’t understand your what you are talking about with fuel pump/mount? What does that have to do with the oil evac setup

 

He's returning his oil through the plate where the stock mechanical fuel pump would mount.
What do you consider excessive blow by? With only 40 miles on it, maybe do a leak down, run it some more, and check it again.

 

No oil in charge pipe. Yes reservoir is vented. Turbos are mounted too low for normal gravity drain. Reservoir is empty after I run the engine and the scavenger pump is running. Fuel pump mount is being used to pump return oil back in crankcase. I will research the scavenger pump to see how much pressure it is putting back into crankcase. This might be the problem.
pump specs:
12v Low Mount Rear Bronze Gear 12 volts Performance fuel Oil Scavenge Pump
Motor: DC 12v
FlowRate: 3.7 GPM
Ports: 3/8? Female JIC
1/2?Barbed Fittings Incuded
Amps: 6A 12v @ 0PSI
Self priming: 5 feet
Lift: 15 feet
Color: Black
Dimensions:
Length: 6.25"
Motor Diameter: 3"
Base: 3" x 4"
oil scavenging has always been an issue.
You might have 50 psi feeding but the slightest restriction in the "drain" will immediately
send oil past the exhaust seals, burning up oil and ruining. In the case of remote mounted
systems, rear mounted systems, or in systems mounted below the engine oil level, some
form of positive scavenging has to be engineered. That is where this pump comes into play.
This pump is a gear pump, the best kind of pump for oil scavenging. Bronze gears.
Brass pump body. No diaphragms to fail like our competitors pumps. Gear design for maximum scavenge.
12vdc with splash resistant wiring. 3/8" female entry and exit with 1/2" barbed fitting included.
The same oil that it scavenges also lubes up its gears.
This is a racing part, please do not expect the product to be quiet.
These pumps are suitable for remote systems as oil scavenge pumps. In this case the engine supplies
the oil pressure and the pump simply returns the oil to a point above the sump level.
Can also be used for various other applications. (Oil transfer, water pump, etc)

 

How is your crankcase vented? Open breathers in the valvecovers? If you have one in each valve cover it's more than enough.

 

I have two breathers on each valve cover

 

I actually think that the scavenger pump is pushing too much PSI into the crankcase. I have a valve attached between the scavenger pump and the engine block so I am going to try closing it partially first. Reservoir is large enough and vented that I will see any issue pretty quick without making a total mess. If this does not work to eliminate the blow-by, I plan on installing a vacuum pump and connecting to both sides of engine via one valve cover breather. Again this is a work in progress so any suggestions are welcome.....

 

I will add , I have done scavenge pumps on several setups. Never had crank case pressure issues from it.

 

i know you said that you have only a few miles on the rebuild . So who knows if the rings broken in? You can do a leakdown and compression test . Or you can remove the turbos just for just for testing to see if the drain system is the culprit.

 

I truly believe that the rings are seated as these miles have been testing at some high rpms and speed. Yes you are correct. Hopefully I can fix without having to remove turbos. If all fails, I will have to do this.
thnaks

 

Don’t you need some sort of vacuum source to remove crank case pressure? That’s why PCV exists? You could run a oil separator if you don’t want the oil building on your turbines, plumbing and intake valves.

 

The only problem with pcv and an open vent at the scavenge is that you are introducing un-metered air in to the motor.
I am rear mount, an-10 to the pump (Very small run of probably only 6 inches) and an-6 after the pump to the valve cover. No reservoir after the turbo, no vent, nothing. I am having no issues, and it might be something for you to try.

Although, it does not make sense to me that the turbo drain system you have could cause the crank case pressurization you are talking about. I really think you have a motor issue. Try capping off your vent and run it. Even if it fixes one issue, but causes another you will have an answer and some direction to what needs attention.

 

How much boost, and what does your timing curve look like? How soon does it make full boost/at what rpm? Do you have a borescope to look at pistons?

 

I am guessing about 12lbs. of boost. Makes full at 3000 rpms according to the msd6al2 timing curve. I am all in at that point. I am going to try a pcv valve and do some testing. thanks

 

How much blowby are you seeing? It's possible you've broke a piston or ring.

 

Not much at idle only on passenger side. More when I accelerate still just one side.

 

You said fresh build but you didn't say if they are cast Pistons? Sounds to me like you've blown it up already. You also didn't say how bad the blow by is. You're focusing on the return pump but there's no way in hell it's causing blow by.

Are you pushing the dipstick out of the tube? Are you spraying oil on the valve covers?

My guess is you went with cast Pistons and have broken a ring land.

Also... Do you have a pvc or other check valve that keeps boost OUT of the crankcase?